HomeMy Public PortalAboutRES-CC-1999-20Resolution 20-99
A RESOLUTION ADOPTING A HAZARD MITIGATION PLAN AND MAP FOR
THE CITY OF MOAB
Whereas, the Moab Governing Body recognizes the need to adopt a hazard mitigation plan to reduce
flooding, fire, and earthquake disasters; and
Whereas, the Moab Governing Body will continue to work with Grand County, the Grand County
Emergency Management Committee, the Grand County Fire Department and other organizations interested
in mitigating disasters; and
Whereas, the City will continue to enforce City zoning and building codes and other health, welfare and
safety laws to mitigate problems associated with floods, fire and earthquakes; and
Whereas, the Moab Governing Body shall continue to develop the Mill Creek Flood Control and Parkway
Project to mitigate flooding and fire hazards; and
Whereas, the Moab Governing Body plans to install detention basins and discharge facilities in Moab area
canyons and install additional runoff collection and conveyance facilities within the City to reduce flood
problems; and
Whereas, the City shall adopt the Master Storm Water Management Plan after it has been reviewed and
accepted by the Moab Governing Body.
NOW THEREFORE, WE, THE GOVERNING BODY OF THE CITY OF MOAB DO
HEREBY COMMIT TO ADOPT THE ATTACHED HAZARD MITIGATION PLAN
AND MAP FOR THE CITY.
session
This resolution shall take effect immediately upon passage.
Passed and adopted by action of the governing body of the City of Moab in open
this 24th day of August, 1999.
CITY OF MOAB
By'*44-doe
Karla Hancock
Mayor
Rachel Ellison
City Recorder
Moab
Hazard Mitigation
Plan
M®AB C T
HAZARD MITIGATI
*
N PLAN
MOAB CITY
HAZARD MITIGATION PLAN
INCLUDES:
MOAB HAZARD MITIGATION MAP
MOAB MASTER STORM WATER
MANAGEMENT PLAN
(EXCLUDING THE APPENDIX)
PREPARED BY: VERSAR, INC.
AMERICAN FORK, UTAH
AUGUST 1999
WILDFIRE HAZARD AND RISK ANALYSIS
FOR GRAND COUNTY
PREPARED BY: FRED MAY, STATE HAZARD MITIGATION OFFICER
UTAH DIVISION OF COMPREHENSIVE EMERGENCY MANAGEMENT
AUGUST 1996
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MOAB CITY
MASTER STORM WATER
MANAGEMENT PLAN
PREPARED BY:
VE.RSAR, INC.
AMERICAN FORK, UTAH
AUGUST 1999
TABLE OF CONTENTS
Chapter page
1. Executive Summary 1-1
2. Introduction and Methodology 2-1
3. Existing Conditions 3-1
4. Future Conditions 4-1
5. Basin Delineation and Hydrology 5-1
6. Computer Modeling and Results 6-1
7. Prioritization and Funding Opportunities 7-1
8. Recommendations 8-1
Figures and Tables
Figure 1 Storm Drain Study Area 2-4
Figure 2 Storm Drain Study Geologic Areas 2-5
Table 5-1(A) Precipitation and Duration Data 5-2
Table 5-1(B) Intensity and Duration Data 5-2
Table 5-2 Drainage Coefficients for Major Basin Areas 5-2
Table 7-1 Improvement Prioritization 7-2
1 Executive Summary
INTRODUCTION / OBJECTIVES
The area encompassed by Moab City has experienced significant flooding due to several recent
storm events. Both extreme localized flooding and overall system failure have resulted in serious
concern toward engineering analysis and correction of these deficiencies.
Much of Moab City is fully developed with both an extensive central business district and
residential properties. This build -out is especially prevalent within areas on the east portion of the
city which abuts against rock bluffs that direct high volumes of runoff at high rates into the
developed areas. A comprehensive management approach to solving flooding problems will
emphasize the collection of storm runoff from these areas within detention basins which will lower
runoff discharge by releasing runoff over a longer time period. Better storm water collection and
conveyance facilities within the developed areas will also be necessary to correct extensive
deficiencies within the existing storm drain infrastructure. Due to extensive build -out, complete
elimination of all localized surface runoff would appear to be unfeasible, but design of a better
collection and conveyance to mitigate a significant portion of the runoff damage will be the
objective. In general, the underlying purpose of this storm water management plan will be
to keep people from the water, keep the water from the people, while at the same time
protecting or enhancing the environment.
Runoff within undeveloped areas principally in the west and north portions of Moab City will also
need to be addressed by installation of storm drainage facilities as part of the development process
and in conformance with the analysis and recommendations of this study.
PROBLEM AREAS
Problem areas can generally be classified into three general categories:
1. Localized flooding most principally on the east portion of the city which is due to
inadequate detention, collection, and conveyance facilities. An example of this is the
existing Tusher detention basin which has sufficient capacity, but discharge flows are
directed into the street downstream with no direct connection to a drainage outlet such as
Mill Creek. Another example is the area of the old Kelling Dam, which in the past
collected some of the bluff runoff north of Center Street, but no longer exists or is not in
service.
1-1
2. Generalized flooding due to the inadequate detention of water which then collects within
the existing roadway and is directed across the city toward eventual release into the
Colorado River. In combination with detention deficiencies, adequate collection and
conveyance facilities are not in place to remove runoff from the street area, and therefore,
flooding issues are spread across the city with properties in low lying areas experiencing
the brunt of the impact. An example of this is the area surrounding the city park located at
100 West and 400 North. Significant runoff generated on the east portion of the city
makes it across Main Street and into an undersized concrete waterway within the park
which directs the flow onto the very flat 400 North roadway. These conditions result in
the 400 North roadway functioning as an inadequate drainage channel which extends
flooding impacts to adjacent properties and to properties downstream.
3. Continued decline in use of historical storm drainage conveyance facilities such as
irrigation ditches and piping create additional storm drainage problems. Historically, much
of the area now developed within Moab City was serviced with regard to storm water
runoff by long-standing irrigation facilities. Recently, the Moab Irrigation Company
installed a pressurized system utilizing much of their existing piping as casing for this new
system. Also, much of the traditional irrigation system is either old or in poor condition.
Utilizing these facilities for storm drainage conveyance is possible according to Moab City
Public Works, but appears to have serious drawbacks due to concerns such as age,
minimal capacity, and maintenance difficulties due to locations on or near private property.
METHODOLOGY / ASSUMPTIONS
Engineering analyses included the introduction of 10-year (piping) and 100-year (detention) storm
events within the Moab City area including rock bluffs east and south of the city. These areas
were broken into major basins and sub -basin areas based upon runoff characteristics of the
existing terrain as developed from a computer generated digital terrain model. Runoff coefficients
were then developed using soil data classified by the Soil Conservation Service (SCS). The
Rational Method was used to calculate surface runoff and results of these runoff conditions were
then modeled via StormCAD, a storm sewer design and analysis software package, which
provided an in-depth analysis of characteristics of the proposed storm drain improvements
including sizes, material types, flow constraints, and problem areas.
RECOMMENDATIONS
Based upon the objective to provide a comprehensive management approach to significantly
improve runoff collection and reduce flooding impacts, the following general improvements are
recommended (as depicted on Figure 3 in Appendix E):
1-2
Installation of new detention basins at the following locations: Walker Canyon, Kelling
Dam, Stewart Canyon, and Williams Way. Also recommended is installation of piping to
direct basin discharge into appropriate drainage outlet areas such as Mill Creek or the
wetland areas west of Moab City.
2. Improvement of discharge facilities from the existing Tusher Canyon, White Canyon, and
Johnson Canyon detention basins. This would consist of installation of discharge piping
within the existing roadway from the present outlet of the basins to eventual discharge into
Mill Creek.
3. Installation of additional runoff collection and conveyance facilities within the developed
portion of Moab City to address runoff within lower elevation areas.
Runoff within undeveloped areas should be addressed as part of the development process
by requiring development to build proposed drainage facilities consistent with city plans.
5. Coordination and agreements should be developed to address runoff from areas within
Grand County, which currently may be directed into Moab City.
6. Funding mechanisms such as implementation of a storm drain utility, bonding, and Utah
Department of Transportation participation should be developed to begin a phased
program of storm drain upgrades based upon priorities established within this study (see
Table 7-1).
1-3
2 Introduction and Methodolou
INTRODUCTION / OBJECTIVES
Moab City has experienced periods of substantial economic and population growth over its
history. Most notable in recent memory is the boom of the Uranium industry in 1960's. Moab
City is currently experiencing another period of economic growth driven by the tourism industry
which has spurred strong commercial growth to accommodate the influx of visitors to the area.
These relatively disconnected periods of growth have developed a challenging environment for
development of a storm water management program within the city to support a current
population of approximately 5,000 people.
Much of Moab City is developed, but most principally in the areas east of 500 West and north of
Mill Creek Drive. Much of the past residential and commercial growth within these areas
occurred some years ago without a comprehensive storm drain management program to
adequately address the impacts of the growth. Therefore, the development of the storm drainage
infrastructure within the city has been focused on solving very localized development needs
without addressing the effect of significant upstream runoff constraints. In addition, much of the
pre development storm runoff was managed via irrigation facilities which are now quite old and
have since been replaced with a pressurized system. These factors have resulted in a storm
drainage collection and conveyance system that is seriously inadequate to address expected design
storm events.
The objectives of this study are outlined as follows:
l . Identify a study area based on Moab City's currently recognized boundaries, along with
specific areas of anticipated growth north of Moab. In association with growth
considerations is the estimation of build -out parameters based upon city zoning plans and
expectations for future growth.
2. Establish design criteria for this master storm water management plan based upon the goal
to develop a comprehensive plan leading toward a system with a level of service sufficient
to mitigate the extensive tlooding conditions experienced within the city during design
storm events.
3. Update and improve existing storm water facilities, including storm sewers, curb and
gutter and catch basins, detention ponds, and ditch facilities.
4. Analyze and establish detention requirements for addressing the flow regime off the rock
bluffs east and south of the city.
5. Establish primary storm drain conveyance systems and associated sub -basin drainage areas
with their boundaries.
2-1
6. Calculate the storm water runoff flow projections for each primary storm drain at build -
out through the use of a cornputer modeling system.
7. Prioritize storm drainage improvements based upon a matrix evaluation of runoff impacts.
Based on these objectives and study findings, this plan presents conceptual design
recommendations for the storm drain management system. The recommendations include the use
of detention facilities and existing ditch facilities for storm water management.
DESCRIPTION OF THE STUDY AREA
The study area includes the current portions of land within Moab City's boundary (see Figure I).
Also under study is an area of approximately 500 feet in width north of the current city boundary
and adjacent to Highway 191. This property is currently within Grand County but in the future
may be within Moab City due to the need to provide municipal services. The area west of the
existing city boundaries from Kane Creek Boulevard to the Colorado River was not covered
within the study area. In the event this area is annexed into Moab City in the future, it would be
necessary to re-evaluate the inclusion of this area as part of the storm drainage improvements
recommended herein.
The study area is bounded generally by the Colorado River on the north and west, and rock bluffs
located east and south of the city. Moab City also is currently bounded by Grand County on the
north and the south. The total approximate area addressed in this plan is 3,920 acres or
approximately 6.1 square miles.
Ground elevations on the valley floor range from approximately 3,960 feet to 4,160 feet above
sea level. Rock bluffs east and south of the city extend to maximum contributing elevations of
approximately 4,680 feet and 5,000 feet, respectively, above sea level. Drainage on the valley
floor generally flows northwesterly toward the Colorado River. Mill Creek and Pack Creek are
natural drainage channels that collect and convey storm water runoff from the rock bluffs and off
the valley floor. These creeks are well defined and carry significant flows as evidenced by a
recent Moab City estimate of nearly 18,000 cubic feet per second of water within the Mill Creek
channel at approximately 500 West. Much of the surface runoff is either collected within these
creeks or within the wetland areas west of the city and is eventually drained into the Colorado
River.
The climate is and with annual rainfall averaging approximately 9.0 inches for the study area.
Average total snowfall for the area is 10.1 inches. Temperature averages generally range from a
high of 100 degrees Fahrenheit in the summer to a low of 20 degrees Fahrenheit in the winter (see
page B-1, Appendix B).
2-2
Soils in the study area range from well -drained gravelly silty loams to dry rock outcrop complex
soils Figure 2 on page 2-5 details the area of soil classification overlaid on top of an aenal map
of Moab City
2-3
METHODOLOGY
HYDROLOGY: The Rational Method was used to calculate storm water runoff. This method is
felt to be sufficiently accurate for the conditions in Moab based upon this method's applicability
for estimating storm peak runoff in small urban and rural watersheds. The method provides a
direct evaluation of the peak rate of runoff at any point in the watershed area based upon rainfall
rates, drainage area, and a coefficient of runoff representing a ratio of runoff to rainfall. The rock
bluff basin areas (see Figure 1) were evaluated using this method and reviewed in relation to
another method, the SCS method, to verify Rational Method results.
COMPUTER MODELING: This study utilizes a storm drain computer modeling program to
more accurately project storm water flows, also using the Rational Method. Information used as
a basis for modeling included field survey data, aerial topographic base maps developed by Moab
City, United States Geologic Survey Quadrangle maps and topographic information, Moab City
official zoning map, and system operational status reports from Moab City staff. StormCAD, a
storm sewer design and analysis software package was used to model the existing and future
storm drainage systems. This program is a user-friendly system that analyzes a variety of system
conditions. Rainfall information can be integrated either through rainfall tables, equations, or
National Weather Service's Hydro-35 data (NOAA). In this study, rainfall tables based upon a
Utah State University study were found to be nearly identical to the National Weather Service's
Hydro-35 data and were, therefore, implemented herein. StormCAD also evaluates various
conveyance elements including circular pipes, arch pipes, and box culverts which is very useful as
there are a variety of conveyance features in Moab presently in use.
Using StormCAD, primary drainage basins were established and subareas for each primary drain
were developed with boundaries which follow features affecting drainage, such as natural ground
contours, streets, ditches, etc. (see Figure 4 in Appendix E). The computer program analyzes
each subarea, taking into account runoff coefficients, distances through the subarea, and slopes
within the area. Based on these conditions, the program calculates projected flow rates from the
subarea for the design year storm. StonuCAD then combines these subareas to determine the size
of storm sewer piping or equivalent open channel size required to corny the cumulative flows.
The program uses a set of variables in the calculation of flow and in the sizing of a proposed
system. They include a rational coefficient, C, for type of surface area being analyzed, i, for
rainfall intensity (inches/hour) and A for area (acres), for the Rational Method formula Q=CiA, to
calculate flow, Q, in cubic feet per second (cfs). Other variables include type of pipe, which
affects the roughness coefficient, slope of pipe, depth of pipe (minimum and maximum), and
design year storm, which is determined from intensity -duration -frequency curves. All of these
variables can be modified in an iterative design process to maximize the functionality of the storm
water management system.
RAINFALL INTENSITY / DURATION CURVES: Rainfall intensity/duration curves were
developed using information and methods based upon the following sources:
2-6
1. Estimated Return Periods for Short Duration Precipitation in Utah, E.
Arlo Richardson, Utah State University, 1971.
2. Precipitation - Frequency Atlas of the Western United States, Volume VI -
Utah, J. F. Miller, et al., National Oceanic and Atmospheric Administration
Atlas 2, 1973.
The curves were evaluated and compared (see Appendix B, page B-1). The results from these
well -recognized sources, which are used by many municipalities, were nearly identical. Therefore,
values within the Utah State University study were used to calculate storm runoff rates.
DESIGN CRITERIA AND ASSUMPTIONS: For purposes of approximating storm water runoff
for this master plan, the following design assumptions were used:
Design year return period is 10-year for collection system piping. The detention
basins are designed for a 100-year storm. These assumptions are consistent with the
proposed Moab City Public Improvement Specifications.
The Rational Coefficient C for valley areas of Moab varied from 0.40 to 0.45, which
represents a composite coefficient based upon full buildout of the city. This
composite coefficient takes into account impervious area as well as soil permeability
consistent with general residential and commercial development pattems. The
Rational Coefficient C for rock bluff areas is based upon soil composition and
percentage of respective soil types within each basin area (see Section 5 of this
study for details of each basin). The land use considered in Moab will be a
combination of single family residential and commercial properties for the purposes
of this study.
Inlet time has been determined for the subareas with the equation:
T = [1.8 x (1.1-C) x D12] / S'f3 , where
"C" is the runoff coefficient,
"D" is the distance (in feet) to the most remote point of the
subarea from the inlet, and
"S" is the average slope (in percentage) from the remote
point to the inlet.
(Source: Denver Regional Council of Governments Urban Storm Drainage Criteria
Manual, March 1969, with Updates, May 1984)
All storm drain piping was designed with a Manning's roughness coefficient of
n = 0.013, which corresponds to a smooth lined pipe. For simplicity, open channels
and the creeks have been analyzed as pipes as well. This has provided a projected
2-7
flow for that segment of the system. This flow can be used to determine the
equivalent open channel needed in the system.
Pipe slopes were determined from elevation contours. Actual pipe slopes will need
to be determined during final design.
Existing facilities have been analyzed as part of this study, and will be used when
projected flows are handled. When these facilities are inadequate, they will be
replaced as required.
Detention basins are used to reduce pipe sizes and maximize the cost-effectiveness
of the system. Approximate sizes have been developed with a generalized routing
routine to use as a guide in siting these facilities. Actual size and configuration will
need to be determined during final design.
Sumps were not incorporated in the analysis. It was assumed that all surface runoff
was to be conveyed out of the subsystem.
Modeling within drainage basins assumes the hydrologic process can be represented
by parameters reflecting average conditions within each sub -basin area.
Small localized flooding areas will not be modeled or studied as this level of detail is
not generally consistent with master planning efforts. In addition, the overall failure
of the existing storm drain management system makes analysis of localized problems
difficult without also considering significant deficiencies upstream.
Storm flows will be calculated assuming no street detention. Runoff in excess of
collection system capacity is assumed to flow to the next down gradient sub -basin
with no street detention. Due to the extensive nature of urban development, street
detention is undesirable in the long term management system solution. At present,
actual peak flows are generally directed within the existing roadways which
highlight the need for improvements.
2-8
3 Existing conditions
TOPOGRAPHY
The study area is located east and south of the Colorado River and is bounded by steep rock
bluffs on the east and south of the City. Slopes of the bluff areas meeting development on the
valley floor are very steep, ranging from 10 to 25 percent on average. Topography on the valley
floor is very mild to flat with average slopes generally ranging from 0.5 to 1 percent. Drainage
patterns generally slope northwesterly into Mill Creek, Pack Creek, and wetland areas west of the
City.
SOILS
The Soil Conservation Service (SCS) 1991 study of the Canyonlands Area indicates the soils
within the study area range from well drained silty soils to impervious rock (see Figure 2 in
Section 2). Soils on the bluffs east and south of the City fall into Hydrologic Soil Groups (HSG)
B, C, and D. These areas are classified to be made up of impervious rock ranging in percentage
from 20 to 90 percent depending upon location. Based upon the soil makeup, permeability in
these areas is considered by the SCS to be generally moderate which translates into medium to
rapid runoff conditions.
The SCS has classified soils within the valley area, which contains most of the developed area of
Moab City, as being HSG A and B, depending upon location. Permeability in this area is
considered by the SCS to be moderate to rapid which translates into slow to medium runoff
conditions.
LAND USE
Existing land use within the study area is generally developed residential or commercial, as
depicted within the official zoning map of Moab City dated July 28, 1998. Undeveloped areas,
principally within the south and west portions of the City, are generally zoned as RA-1 which
combines agricultural and residential uses. These undeveloped areas are generally natural areas
that do not support significant agricultural use at the present time. It is anticipated that in the
future these areas will develop into residential use.
3-1
NATURAL DRAINAGE
Two major natural drainages run from east to west through the Moab area. These drainages, Mill
Creek and Pack Creek, start well east and south of the study area and flow northwesterly to the
Colorado River. These drainages have been historically utilized for storm drainage runoff,
throughout their length, by both Moab City and Grand County.
Irrigation ditches and channels have also been historically used for collection and discharge of
storm drainage runoff. The extent of this use has reduced over time as the agricultural areas
within Moab City have continued to be replaced by residential and commercial development. In
addition, conversion by the Irrigation Company to a pressurized distribution system has
accelerated the decline in the availability and condition of these facilities.
MAJOR ROADWAYS
State Highway 191 traverses through the community from south to north. Storm drainage
facilities servicing this roadway generally collect surface runoff and discharge it immediately into
adjacent city roads. The serviceability of these collection facilities is in question due to many of
the catch basins and pipes being choked with sediment or debris.
Major city streets providing north -south routes include 400 East and 500 West. East -west routes
of major significance include Mill Creek Drive, Center Street, Kane Creek Boulevard, and 400
North.
EXISTING STORM WATER MANAGEMENT SYSTEM
As part of the system analysis, an inventory of the existing drainage and irrigation facilities was
compiled by interviewing Moab City employees, research of "As -Built" records, field surveys and
visual observations. Figure 5 in Appendix E titled "Moab City Existing Drainage System"
presents the compilation of this information.
The existing drainage features were field surveyed to determine location and elevation based upon
the Moab City Datum and Coordinate System. This system is based upon the Grand County
horizontal control network, and vertical control is based upon United States Geological Survey
(USGS) monument #JM0311 located on Main Street just north of Center Street in Moab. Maps
showing contours were previously generated by Moab City from aerial surveys based upon the
Grand County vertical control network. Differences may be noted as to the contour elevations
and actual survey elevations which are based upon the USGS monument. For consistent study
evaluation, the contour elevations have been utilized to develop elevation and slope criteria.
Actual design of future storm drainage facilities will be based upon the elevations generated from
the Moab City Datum and Coordinate System.
3-2
The existing drainage system consists of the following general elements as shown on Figure 5 in
Appendix E:
Upper check dams - which are small, 6-
to 8-foot high, rock dam structures that
have been constructed at various
locations across natural drainage channels
upon the rock bluffs east of the City.
These features (see adjacent pictures)
provide an intermediate flood control
mechanism above the existing detention
facilities, which aids in slowing down the runoff and
controls sediment release. In order to provide a
conservative approach to basin hydrology development,
engineering analyses did not consider the effects of these
features as their locations and their relative benefit to
basin runoff is uncertain_ Therefore, a safety factor may
be built into the hydrology calculations dependant upon
the effectiveness of these features.
Check Dams on Rock Bluffs
2. Detention Basins - located at Tusher Canyon, White Canyon, and Johnson Canyon. Each
of these basins has been functioning reasonably well according to historical investigations.
The Tusher Canyon and White Canyon Dams are overseen by the Utah State Department
of Natural Resources Dam Safety Division. Their analysis (see Appendix D, pages D-1
through D4) indicates that the dam and spillway are functioning adequately, with some
need for general maintenance or minor repairs. Maintenance of the Johnson Canyon Dam
is made difficult due to its location on private property.
White Canton Detention Detention Basin Inlet
Tusher Camvon Detention Johnson Canyon Outlet
3-3
3. Detention basin discharge - The discharge
from the existing basins is released via
piping either into the street or into small
drainage channels (see adjacent pictures).
This condition creates problems as
discharge is not readily contained in these
channel features and tends to sheet flow
and pond at low points below the basins.
Downstream Discharge Points
4. Collection facilities - which are principally catch basins, are
scattered throughout the City. The catch basins have grate
openings of various sizes with several having been
fabricated to a larger than normal size to attempt to
alleviate upstream collection deficiencies. The majority of
the catch basins are located near Main Street (State Route
191) and near Kane Creek Boulevard. The serviceability of
these features generally appears to be good with some
exceptions noted during visual inspections of the facilities on
Main Street.
Collection on 400 North and
Main Street
S. Pipe conveyance facilities - which generally collect localized
runoff, and subsequently direct it to an adjacent street or
drainage feature. Piping is generally in fair condition. Older
piping such as the 30-inch converted irrigation line on
400 North and the 24-inch line in 200 Sown are
functional, but due to their age may require additional
maintenance attention in the future. ;.
Pinkie on Kane Creek Blvd. and
Main Street '
3-4
6. Ditches and irrigation facilities - The existing ditches and irrigation facilities remaining in
use for storm drainage use are generally only capable of meeting localized runoff
requirements. Upstream runoff not collected presently makes its way into these facilities
but overwhelms the capacity, and therefore, spreads the flooding concems. The ditches in
use are highly vegetated and have relatively flat slopes in the range of 0.3 to 1.0 percent.
Existing Ditch Features
8. Major drainage channels and wetland areas - The outlet for the runoff within the study
area is into these features, and then subsequently into the Colorado River. The capacity of
these features by all indications is sufficient to address existing storm drainage runoff. A
revision to FEMA floodplain areas is currently being pursued by Moab City which will
more accurately define the channel capacity for Mill Creek, but capacities as much
as18,000 cubic feet per second are anticipated. These values appear to indicate sufficient
capacity to accommodate future runoff as represented within this study.
Various points on the Mill Creek
3-5
PROBLEM AREAS
As previously indicated, the existing stone drainage system is inadequate to address frequent
flooding problems The deficiencies within the existing system are wide ranging but specific areas
of concern are as follows
1 High rates of runoff from the rock bluffs in many areas is not contained and floods across
the entire city system. This is especially true within the areas of Walker Canyon, the old
Kelling Dam, and Stewart Canyon Areas immediately downstream from these locations
have experienced significant flooding during storm events that are judged by local officials
to be within the range of precipitation values expected from a 10-year storm event used as
a basis for design within this study
2 Areas immediately below existing detention basins at Tusher Canyon, Wlute Canyon, and
Johnson Canyon have experienced flooding principally due to the release of discharge
flows into the street or into inadequate channels This problem is localized dependant
upon topography and maintenance of existing drainage features such as ditches
3 Inadequate conveyance of runoff away from the Main Street area combined with
uncollected runoff up -gradient create several concerns west of Main Street Most
significant is the runoff directed into 100 West, and then subsequently down 400 North
until it is discharged into wetland areas near the Moab City wastewater plant The
existing 30-inch storm drain in 400 North is considerably undersized, and 400 North
essentially acts as a drainage channel which impedes traffic and floods low-lying
properties
4 Surface runoff from the rock bluffs south of the City directs runoff into the area of the
Moab City Shops This concentrated flow across Kane Creek Boulevard converts to sheet
flow flooding City facilities and homes north of this area before eventually being
discharged into Mdl Creek.
5 Flooding across Main Street at approximately 300 North to the intersection of the
highway with 500 West is a significant problem for local businesses This problem is
related to the lack of detention above this area, but is also due to the fact that no
collection and conveyance facilities are available to service the runoff
6 Localized problem areas such as the area on 100 East near the Fire Station are due to
inadequate collection facilities and no effective way to convey the water from the area
7 Downtown areas along Main Street from Mill Creek to approximately the intersection of
400 East along Ifighway 191 experience localized flooding concerns Minimal collection
facilities exist along the highway which translates into runoff being inadequately
maintained within the roadway area untd it reaches a creek crossing These conditions
3-6
appear inadequate to address the drainage being collected at .he highway because the
highway acts as a natural drainage barrier due to the crown of the road being as much as
two to three feet above the gutter elevation
8. Areas north of the intersection of 500 West along Highway 191 (some of wluch within
Grand County) contribute to significant runoff sheeting across the highway This appears
to be pnnc►pally a result of inadequate maintenance of an extensive number of existing
cross culverts (see Figure 3 in Appendix E)
3-7
4 Future Conditions
FUTURE DEVELOPMENT
Buildout of the remaining undeveloped portions of the city was based upon zonmg
designations shown on the Official City of Moab Zone Map date July 28, 1998 It is
expected that residential growth will occur m the majority of these areas In the event
zoning modifications are made, the results of this study model may require review as related
to actual conditions Implementation of the recommendations of this study and the
management plan presented herein, within these areas, will be critical to ensure the
participation of development in instituting adequate storm drainage facilities This will be
necessary to accommodate the increased runoff rate (over existing conditions) generated by
installation of more impervious surfaces
Commercial growth within a comdor along Highway 191 is anticipated from the existing
city boundaries to the Colorado River This property is currently withm Grand County but
may be part of Moab City m the future due to the probable need to provide municipal
services A 500-foot wide corridor along the highway was considered within the study area
in the event Moab City is responsible for future storm drainage issues within this area
Development of the areas south of Moab City in Grand County will require coordinated
efforts to accept storm runoff from the county into areas adjacent to Moab City Sheet 5 of
Figure 4-1 of "The Spanish Valley Master Storm Water Plan" dated May 1979, prepared
for Grand County, mdicates the need to install a 54-mch cross culvert replacing an existing
29"x18" arch culvert at the mtersection of SR-191 and 400 East A flow rate of
approximately 120 cubic feet per second is planned to be collected from the area within
Grand County and conveyed across the highway and discharged mto an existing ditch This
improvement is rated as the highest pnonty m the county study and could be constructed at
any time Coordination of this installation to ensure adequate conveyance of flows north
into Pack Creek will be necessary
WATER QUALITY STANDARDS AND DISCHARGE PERMITTING
Water quality for storm water discharges to surface streams and bodies of water is
regulated by the Environmental Protection Agency (EPA), which is administered by the
Utah State Division of Environmental Quality (DEQ) Discharges to streams or lakes can
be required to have a discharge permit, as regulated under the National Pollution Discharge
Ehmination System (NPDES) permitting Utah State DEQ implements the NPDES through
its own Utah Pollution Discharge Elimination System (UPDES) pernutting program (see
4-1
Appendix D) Moab is currently not subject to a UPDES permit for storm water discharge
as the present guidelines only require permits for municipalities of 100,000 population and
greater The EPA's proposed modifications to their regulations were out for public
comment until March 1, 1999 (40 CFR 122, 123) Implementation will take place May
2002,'usmg 2000 census population figures Communities of 10,000 population and greater
will be subject to these regulations However, it appears they will apply to industnal stone
water and construction sites of one acre and greater only. Cities will be required to draft a
storm water management plan to be approved by the State More information wdl be
distnbuted to the cities as that date approaches Due to the current and projected growth
rate of the population of Moab City, these regulations do not appear to be of significance
for some time
The DEQ currently requires some -storm water sumps related to industnal runoff and
injection pumps to be permitted They do not require municipalities to have permits for
normal street storm sumps EPA has written new regulations for sumps for mdustnal sites
only They currently have these regulations out for public comment (40 CFR 144 86)
Sumps are also considered as part of the well protection program as a point source of
potential pollution Their use is not allowed within the 100-foot radius of a culmary well
EPA will not likely regulate normal street storm water sumps However, it is recommended
that Moab voluntanly implement Best Management Practices (BMPs) to reduce nsk of
groundwater pollution This would include educattng the public about possible risks of
polluting groundwater by discharging waste materials m any existing sumps (drained oil,
gasoline spills in the road, etc.) The DEQ suggests that the city consider painting a
warning on the face of curbs above sumps They also recommend the use of detention
basins up gradient from sumps wtuch could help contain pollutants and would enhance clean
up of hazardous waste spills should such emergenctes occur It is proposed as part of the
Moab City Pubhc Improvement Specificattons, currently under review by city stag that
sumps only be used in rare instances and only after acceptance by the Pubhc Works
Department and the City Engineer
4-2
5 Basin Delineation and Hydrology
BASIN DELINEATION
Major drainage basins were delineated based upon natural discharge locations within the
study area and on ultimate discharge into major dramage channels The major basin
delineation is shown on Figure 4 in Appendix E These major basins were developed to
facilitate the planning of detention basins and estimation of required pipe sizes Sub -basins
withm the major basin areas within the valley portion of the study area were also delineated
to facilitate detailed modeling of the drainage area and are depicted in modeling results in
Appendix A
Drainage basin boundaries on the rock bluffs east and south of the city were developed
using flow regimes generated by Digital Terrain Model (DTM) of the area and use of a
hydrology tracking feature within the Intergraph Inroads software package. This package
easily allowed the delineation of drainage flow patterns off the bluffs from any pomt within
the major basin area and generally developed the location of concentrated discharge into
detention facilities. Also developed was maximum extent of contributions off these upper
bluff areas into the valley portion of the study area.
Major drainage basins within the valley portion of the study area were developed utilizing
the same methods as detailed above while considering the locations of planned
improvements
HYDROLOGY
As discussed earlier in Section 2, the Rational Method was used to determine major basin
hydrology Areas based upon the major basin delineation were combined with design storm
events along with a composite runoff coefficient to determine a runoff rate which was
subsequently integrated within the storm drain model. As discussed previously in Section 2
and also detailed in Tables 5-1(A) and 5-1(B), the rainfall data below in inches, from the
following study was used as basis for precipitation data: Eshmated Return Periods for
Short Duration Precipitation m Utah, E Arlo Richardson, Utah State University, 1971.
TABLE 5-1(A)
5-1
(
(
TABLE 5-1(A)
PRECIPITATION AND DURATION DATA
DURATION
Return
Penod
5
min
10
min
15
min
30
min
1 Hr.
2 Hr
3 Hr
6 Hr
12 Hr
24 Hr
10-year
24
37
47
65
82
9
98
118
136
154
100-year
35
54
68
94
1 19
1 33
1 46
1 80
2 10
2 41
TABLE 5-1(B)
INTENSITY AND DURATION DATA
Return
Period
5
min
10
min
15
min
30
nun
1 Hr.
2 Hr
3 Hr
6 Hr
12 Hr
24 Hr
10-year
2 88
2 22
1.88
1 30
82
45
33
20
11
06
100-year
4 20
3 24
2.72
1 88
1.19
67
49
.30
18
10
Composite runoff coefficients were developed for each of the major basin areas based upon
the soil conditions and runoff coefficients for specific terrain conditions as detailed in
Design and Construction of Sanitary and Storm Sewers ASCE Manual of Practice No. 37,
1970, Revised by D. Earl Jones, Jr The results of the composite runoff coefficient
calculations are as follows.
TABLE 5-2
DRAINAGE COEFFICIENTS FOR MAJOR BASIN AREAS
MAJOR
BASIN
BASIN
COMPOSITION
BASIN COMPOSITE
COEFFICIENT (C)
REMARKS
AREA 1 W
70% soil 99, 30% soil 62
45
Bluff area
AREA 2 W
20% soil 62, 15% soil 88,
65% soil 99
72
Bluff and
developed area
5-2
AREA 1 E
15% soil 61, 85% soil 73
.57
Drains to Mill
Creek
AREA 2 E
10% soil 80, 90% soil 73
.58
Drains to Tusher
detention
AREA 3 E
30% soil 72, 70% soil 73
.63
Drains to White
Canyon detention
AREA 4 E
25% soil 72, 75% soil 73
.63
Drains to Johnson
Canyon detention
AREA 5 E
25% soil 72,,75% soil 73
.63
Drains to Kelling
Dam area
AREA 6 E
50% soil 72, 50% soil 73
.65
Drains to Stewart
Canyon area
AREA 7 E
50% soil 72, 50% soil 73
.65
Drainage across
SR-191
AREA 8 E
50% soil 72, 50% soil 73
.65
Drainage across
SR-191
AREA 9 E
30% soil 72, 70% soil 73
.63
Drains to Walker
Canyon area
Coefficients are based upon future buildout of developable areas below bluffs and within
major drainage basins.
DETENTION BASIN DISCHARGE
Discharge rates from each of the existing detention basins at Tusher Canyon, White
Canyon, and Johnson Canyon were developed based upon the capacity of the discharge
piping. Also taken into account was the pressure head applied at the inlet of the piping at
the bottom of the basin. A culvert analysis based upon entrance control characteristics was
performed to determine additional discharge added to the outlet piping via pressure head.
It was assumed the basin was full to the top of the dam in order to provide a conservative
evaluation of the resultant pressure head. Using pipe sizes, types, and slopes based upon
field survey investigations of each location, a discharge flow rate was determined (see
Summary on Page C-10 in Appendix C). This flow rate was subsequently used for
modeling proposed downstream improvements as covered within Appendix A.
5-3
6 Computer Modeling and Results
COMPUTER MODELING
Once the existing facilities were identified, the proposed primary storm water management
system was laid out and the drainage piping was evaluated using the 10-year return period
storm event Analysis also included a 100-year return period storm event used to estimate
drainage basin storage requirements. A compilation of the tabulated data for each proposed
detention basin and pipe string is contained in the section titled "Primary Drain Modeling
Data" in Appendix A. Also included with this data is a map of the sub -basin drainage areas
modeled within the study area An overview of the proposed system is presented on the
map titled "Moab City Proposed Stone Drainage System" on Figure 3 in Appendix E
Pipe sizes and detention basin locations presented in the data are preliminary in nature and
each drain should be subjected to a detailed evaluation pnor to final design Also, for final
design activities, subarea discharges should be reviewed and refined as necessary
PIPE ROUTING AND SIZING
Storm drain piping alignments were based upon topography, available comdors, and outfall
locations The pipe sizes were developed based upon the Manning equation for flow
assuming gravity conditions The gravity design size gives the city a factor of safety over
pipe sizes that may be used when utilizing the pipes under a pressure head condition. Pipe
size reductions to include pressure head should only be considered on a case by case basis
with the aid of final design level information
PROPOSED DETENTION BASINS
Detention basins were proposed at the following locations to lower the peak runoff rate
from the rock bluff areas east of the city. Walker Canyon, Kelling Dam, and Stewart
Canyon (see Figure 3 in Appendix E) These detention basins will be utilized to reduce
peak flows from a design storm event by detaining the excess water and releasing it at a
restricted rate over a longer period of time Therefore, the use of these detention basins will
reduce required pipe sizes downstream and the resultant corridor needed for pipeline '
construction Detention basins in the locations proposed will also be extremely useful for
collection of sediment and debris being transported within storm water runoff
6-1
A detention basin was also developed in the area of 500 West and Williams Way. The need
for this basin is based upon the need to convey nearly 100 cubic feet per second of water
through this area while traversing very flat slopes of approximately 0.4 percent. Sizes of
pipes of 42 inches, at a minimum, make construction of this line into Mill Creek extremely
difficult due to existing terrain. Therefore, introduction of a detention basin somewhere
west of the developments on Walnut Lane was deemed necessary. Actual location is
somewhat variable between Walnut Lane and ultimate discharge into Mill Creek, but due to
possible development coordination issues it has been shown immediately west of the
existing dead end on Walnut Lane.
A reservoir routing model was developed to predict the amount of discharge based upon a
basin storage capacity, discharge piping characteristics, and an inflow hydrograph
developed from major basin runoff characteristics as detailed in Section 5 of this study. The
detention basins were sized based upon general objectives of a release rate based upon 0.15
cfs per acre of contributing area and a two to three how release period beyond the point of
maximum storage levels. A 100-year stone event was used for generation of the inflow
hydrograph. An outflow analysis for various sizes of discharge piping was developed and
compared to inflow conditions (see Appendix C). Comparison of the storage necessary to
accommodate a selected pipe size was then generated and an estimated storage volume was
then derived.
The detention basin sizing estimated should be reviewed during the design phase when
actual physical design parameters are available.
OPEN CHANNEL CONVEYANCE
The storm drainage management plan presented herein utilizes piped storm water
conveyance to natural outlets assuming full buildout conditions. Interim use of open
channel conveyance in specific locations may be an acceptable short term alternative to
minimize construction costs and allow development to assist in installation of storm drain
piping. Specific areas of possible use include:
On portions of the city shops storm drain improvements, from Kane Creek
Boulevard to Mill Creek.
Expansion of an existing ditch east of 500 West from Williams Way to the Mill
Creek.
Expansion of the existing ditch located at approximately 600 North, extending from
500 West to the west.
6-2
On a proposed drainage corridor extendmg immediately north of Westwood Avenue
from 500 West to the west
On a proposed storm dram hne within the area of the proposed Pear Tree Lane
extension from Mill Creek Dnve to Pack Creek.
Benefits of open channel features include water quality improvements, easier access for
inspection and maintenance, greater flexibility for new connections, and generally lower
costs than piped alternatives Drawbacks to use of open channels mclude accumulation of
debns, potential hazards dunng high flow conditions due to open water, difficulties in
keeping positive drainage in low flow conditions, more day to day maintenance than piped
facilities, requirements for additional easements to expand ditch capacity, and generally not
in keepmg with curb, gutter, and sidewalk improvements
ACCEPTABILITY OF EXISTING FACILITIES
From discussions with city staff existmg facilities m the area of Kane Creek Boulevard and
SR-191 were indicated to be generally meeting demands of design year storm events Due
to this understanding, facilities within this area were not included within the model for
proposed storm water improvements Minor modifications to install additional collection
and conveyance facilities may be appropnate as determined through future observation and
mamtenance activities
Sigruticant runoff amounts were anticipated off the rock bluffs south of Kane Creek
Boulevard at approximately 500 West This area is generally served by natural drainage
channels directing the runoffmto an existmg 36-mch culvert crossing Kane Creek
Boulevard just west of the city shops In discussions with city staff, it was indicated that
the majonty of the flow from this area is channeled through this culvert and that the
capacity of the culvert should be sufficient for consideration of runoff constramts
Therefore, the 36-mch culvert capacity of approximately 45 cubic feet per second was
mtegrated into the model withm this dramage area
Numerous existing culverts extending across SR-191 north of Moab City were identified as
part of this study The serviceability of these culverts is questionable due to apparent
clogging or blocking as reported by Moab City staff. The number and size of the culverts
examined appear to have capacity to reasonably address runoff of the rock bluffs east of this
area For purposes of this study, it was assumed that the existmg culverts, if properly
maintained, would convey runoff across SR-191 and that it would then need to be
addressed It was concluded, due to the number of natural channels and culverts directing
flow across the highway, that collection mto a general storm water conveyance network
west of the highway would be extremely difficult Therefore, it is anhcipated that future
development within a 500-foot corridor along SR-I9I will need to address specific drainage
6-3
constraints as part of the individual developments with an intent to discharge runoff
immediately to the west of this area. This philosophy is consistent with existing runoff
characteristics that currently direct flows westerly across the highway and eventually into
wetland areas and the Colorado River. It may also be necessary for developments in Grand
County occurring farther west than the 500-foot wide corridor to coordinate with Grand
County and Moab City concerning ongoing and future discharge patterns.
GRAND COUNTY COORDINATION
As discussed in Section 4 of this study, Grand County's Master Storm Water Plan shows
the need for a 54-inch culvert crossing of SR 191 and discharge into an existing ditch. The
accommodation of flows from this proposed culvert are not included within this study as the
extent of any future city participation is unknown. Since this area is all currently within the
county but abuts city boundaries, it will be necessary for the city to coordinate with the
county to ensure all discharge from these areas is effectively conveyed to Pack Creek.
Also of concern are areas southwest of city boundaries which by virtue of natural slopes are
expected to drain from areas within the county into areas served by Moab City. The
County Master Storm Water Plan shows the 54-inch culvert discussed earlier and an
additional 24-inch cross culvert on SR-191. It is not clear whether the bluff area south of
Moab City within the county is addressed within the county study. For purposes of this
study, only the area within Moab City south of SR-191 was quantified. The resultant pipe
serving Moab City area only was sized at 15-inch diameter. Preliminary analysis of the
bluff areas and lower areas within the county in this southwest area near Moab City appear
to indicate extensive additional runoff flows that will need to be coordinated between Grand
County and Moab City officials.
ENVIRONMENTAL CONSIDERATIONS
Design and construction of the improvements within this proposed Storm Water
Management Program will require attention to environmental impacts. It is anticipated that
better collection and conveyance facilities will benefit the environment by limiting the
uncontrolled depredation of valley areas caused by extreme flooding off the rock bluffs.
Implementation of the recommended improvements should take into consideration
discharge into streams and wetlands to prevent extensive erosion due to high velocity
discharge. Measures such as rock linings, check dams, and small sedimentation basins or
collection boxes should be considered. Permits coordinated with the U.S. Army Corps of
Engineers can be expected when installation of storm drainage facilities occurs within
existing wetland areas.
6-4
Prioritization and Funding Opportunities
PRIORITIZATION
The proposed improvements were prioritized based upon a matrix evaluation, which ranked
various elements of the characteristics of the existing storm drainage system These
elements were ranked based upon a 0-10 scale where zero is very low impact, five is
medium impact, and 10 is high impact The composite formula result is. BD*(Q+R+C+S)
as based upon the following elements.
✓ Buildout / Damage (BD) - a composite estimation of the area presently built out
which will be serviced by the proposed facilities and the extent to which the city is
incurring risk related to flooding damage This factor was considered most
significant as the current flooding problems require the greatest attention particularly
in the developed areas and also at specific locations which require extensive ongoing
maintenance activities In addition, it is expected that development within the areas
not currently built out will participate in installing storm drain improvements,
thereby relieving some of the economic burden on the existing city residents For
detention basins, buildout / damage estimations are based upon downstream
characteristics as these are the areas benefitted by the installation of these facilities
✓ Runoff Quantity (Q) - an evaluation of runoff quantity serviced by new
improvements as compared to other system elements This factor takes into account
the amount of area serviced and the nature of the land use as developed within the
hydrology analysis inherent within the Rational Method
✓ Residential Flooding (R) - an estimation of residential flooding based upon histoncal
information provided by city staff and experience This factor includes an evaluation
of the residential area as compared to the total area serviced by the associated
improvements
✓ Commercial Flooding (C) - an estimation of commercial flooding based upon
historical information provided by city staff and experience This factor includes an
evaluation of the commercial area as compared to the total area serviced by the
associated improvements
✓ Street Conveyance (S) - An estimation on capacity of existmg streets and other
natural drainage features to carry runoff and the extent to which they are inundated
7-1
TABLE 7-1
IMPROVEMENT PRIORITIZATION
F
9
5 8
8
5
8
241 2
Kelhng Dam
Detention
Stewart
Canyon
Detention
9
5 8
4
9
8
241 2
Walker
Canyon
Detenhon
9 5
4 0,
9
3
9
237 5
t-
400 North
8
3 6
8
8
9
228 8
City Shops
7
4 2
9
9
10
225 4
200 North
8
6 6
8
5
6
204 8
Center Street
(new)
7
5 1
7
6
7
175 7-
McGill Ave
(new)
7 5
4 6
4
8
5
162
Tusher Ave
7
3 7
8
2
9
158 9
200 South
(new)
7
3 3
7
1
8
135 1
McGill Ave.
IMch/Pipe
(upgrades)
5
7 9
4
1
10
114 5
Center Sheet
(upgrades)
5
5 9
2
9
4
104 5 S
t"
200 South
(upgrades)
5
6 7
5
5
4
103 5
Mam Street
5
0 7
3
6
6
78 5
500 West
(upgrades)
5
12
4
1
8
I
71 `
Westwood
Ave North
3
7 2
3
3
8
63 6
Locust Lane
4
16
4
2
4
i
46 4
100 Pact
(upgrades)
4
2 0
3
2
3
40
400 East
4
1 4
2
4
4
45 6
7-2
The ranking of priorities is a subjective analysis based upon data available. Due to the
precision of the overall formula, rankings should be considered in the context of a general
comparison of impacts and needs.
CONSTRUCTION PHASING
Construction sequencing should be considered when implementing the recommended
improvements. Construction of new detention facilities and associated discharge piping at
the same time will provide the most comprehensive solution within a sub -basin area. But
these facilities may be considered for separation due to potential benefits in decreased
overall damages within the subarea. In the event a detention basin is constructed in advance
of installation of discharge piping, some increased localized flooding may occur as the flow
out of the detention basin will be lower than the peak for the entire area but can be expected
to be more concentrated.
It should also be understood that functionality of upstream improvements is dependant upon
the ability of facilities downstream to accommodate runoff discharge. In general,
construction of new pipe lines while utilizing undersized existing pipes downstream (such as
200 South) may be a short term option with the understanding that the undersized pipe may
be surcharged into a pressure flow condition that could be extreme. Examination of these
conditions may be made on a case by case basis as part of more detailed design activities,
but such conditions are not recommended.
OTHER FACTORS AFFECTING PRIORITIES
Ongoing maintenance and construction of roads within the city will affect the scheduling of
storm drainage improvements. There is a large cost savings to be reaped by the city by
constructing drainage improvements during road construction. This may rerult in some
drainage improvements being built ahead of others ranked higher in the prioritization list.
Moab City is currently in the process of developing a road maintenance and priority listing
that when completed will need to be coordinated with the results of this study.
The recommended improvements in this report are developed to address ultimate
development. Recommended improvements within undeveloped areas will need to be
7-3
monitored in relation to future development to ensure inclusion of the proposed storm
water management system described herein.
Installation of recommended improvements does not preclude the need for some additional
localized storm drainage infrastructure. Many of the localized areas now experiencing
flooding problems will be greatly benefitted by the installation of nearby improvements
which are recommended herein. Correction of ongoing localized flooding problems after
much of the nearby storm water management system is in place will need to be handled on a
case by case basis, but the number of problems is expected to be greatly diminished.
FUNDING OPPORTUNITIES
The construction and maintenance of city wide storm drainage management facilities are
expected to require significant financial resources. A financial evaluation of recommended
improvements and development of a capital improvement plan are expected to be developed
subsequent to the acceptance of this master plan by the Moab City Council.
Funding of storm drainage capital improvements can be covered by using general funds, by
bonding and paying back over time, or by development of funds specifically earmarked for
this purpose. Specific options are as follows:
➢ Taxes - use of existing tax revenue or integration of additional tax income.
➢ Grants / Loans - State and Federal Government grants and loans are occasionally
made available for the improvement of waterways and wildlife sanctuaries.
➢ Utility Fees - a fee directed toward all users of the system could be instituted by
ordinance. In general, these fees range from $2.00 to $3.00 per month per
equivalent residence. Fees for more appropriately addressing commercial
development should be based upon the amount of impervious area contributing
runoff to the system.
➢ Impact Fees - an impact fee can be established by ordinance to address impacts of
new development. This would not address the majority of storm drain
improvements needed as they are in areas already developed and are not expected to
serve significant new development within the existing city boundaries.
➢ UDOT Participation - assistance of the Utah Department of Transportation as part
of the Statewide Transportation Improvement Plan (STIP) for improvements related
to SR-191.
74
SRecommendations
RECOMMENDATIONS
✓ The recommended storm drain improvements are shown on Figure 3 in Appendix E
It is recommended that funding methods be established to begin constructing the
pnoritized improvements Costs of construction will need to be formulated as
funding availability is determined and as part of development of a capital
improvement plan expected to be undertaken subsequent to this study
✓ A mechanism for participation between developers and the city should be clearly
defined by ordinance This should include levels of nummum capacity required
through development and the payment of necessary upsrzrng by the city to
accommodate upstream demand An hnpact Fee Study should be undertaken to
assess the potential of addressing future funding of new development storm water
infrastructure needs
✓ It is recommended that the city develop cooperative agreements with the Utah
Department of Transportation (UDOT) to improve collection and transmission of
runoff off near State Highway 191 This would include clarification of maintenance
responsibihties and infrastructure needs A UDOT project is nearing the
commencement of design for SR-191 from Crescent Junction to Moab City
Although the extent of the project limits are not clear, it would be advantageous to
explore possible participation in storm drain system upgrades as part of this project
✓ A cooperative agreement between Moab City and Grand County should be prepared
to address concerns of runoff fiom the county into areas of Moab City
8-1
08/20/00 10 51 FAX 801 4 3770 UTAH DIv CHM
0002/010
4/2/97 Wildfire Hazard and Risk Analysis, Grand County
Page 1
Wildfire Hazard and Risk Analysis, Grand County
Prepared on August August 29, 1996, by Fred May, State Hazard Mitigation Officer,
Utah Division of Comprehensive Emergency MAnagement; Jeff Bench, Grand County
Liaison, Utah Division of Comprehensive Emergency Management; Doug Squire, Grand
County Emergency Management Director; Stan Baker/Bill Zanotti, Utah Division of
Forestry, Fire and State Lands; and
1.0 Small Localized Fire
1.1 Fire spreading upslope
1.1.1 Fire spreading into URWIN community
Castle Valley (fringes): PJ (pinyon- juniper) vegetation, sage and grass.
Estimate at least 50 primary residence structures; est. pop. 200.
Willow Basin: Not a community, just a cabin area. About 40 land owners and
30 secondary structures; a few permanent. Permanent populaton may be
about ten people. Ponderosa pine and oak brush.
Wilson Basin: Lasal Loop Road area. Wilson Mesa, Sand Flats. Estimated
30 structures; mostly primary resmdences. Estimated popiation 50 to 100.
PJ and mountain brush.
Moab: Around the golf course in the southem part of the city. The waterways
through the center of town on MIII Creek and Pack Creek (riparian with
cottonwoods and willows and Russian Olives). Kane Creek Boulevard
(tamarisk). The Matheson Wetlands (tamarisk and willows, a few
cottonwoods) Estimated number of structures 1000; mostly primary and
business; estimated 1,600 some motel visitors.
Hwy 128 Area (River Road area): Runs northeast of Moab along the
Colorado RNer. Estimated 50 structures (including Dewey Area); mainly
primary structures. Estimated population 160 to 200. Tamarisk and sage
brush and a few sands of oak.
Westwater Area: On the Colorado River near the border. About 15
structures; about half primary. Estimated population 10. PJ vegetation.
Dolores Triangle Area: At Colorado state line, bordered by the Dolores
River, Colorado River and the state line. Estimated 10 to 15 structures;
mostly primary structures. Estimated population Is about 10. PJ and sage.
South Book Cliffs: Estimated structures 50; 20 primary. Estimated population
Is about 20. PJ to desert shrub.
Crescent Junction and Thompson: Thompson has hydrants in place
Estimated structures 100, primary residences about 50. Estimated
population 35 at Thompson and another 20 at Crescent Junction. desert
shrub and sage.
Cisco: Eastern Grand County in the Cisco Desert. Estimated structures 3,
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population about 15. Have their own post office. Desert shrub.
Grand County Line to the south: Upper and Lower Spanish Valley,
Estimated structures about 70, including All American Acres and Beeman:
all permanent. Estimated population 200. Sage, grass (Cheat Grass).
Elgin and Hastings: Estimated 30 stuctures; 20 primary. Estimated
population about 30 to 40 people. Tamarisk and desert shrub.
Many other single residence places.
1.1.1.1 Fire station too distant
Moab: 5 minutes or less response time.
Dolores Triangle: 30 minutes.
River Road Area: Castle Valley covers part. 45 minutes on upper end.
Westwater Area: 1.6 hours. From end of October until June, no fire
protection.
South Book Cliffs Area; 1.6 hours
Crescent Junction/Thompson: 15 to 20 minutes.
Cisco: 45 minutes to an hour.
Hastings and Elgin: 20 minutes.
Recommendation: Grand County look at a full time fire warden to help
the other communities to be better prepared.
Recommendation: Have fire fighting equipment on the 1-70 corridor
near Thompson.
1.1.1.1.1 Delay in fire suppression actions
1.1.1.1.1.1 Spreading fire
1.1.1.1.1.1.1 Trapping residents
Willow Basin is of particular concem where people could be
trapped.
Wilson Mesa is also of concern.
Most other areas have escape routes with dual access.
Wetlands and Waterways area there is a danger of trapping
people where people are both residents and visitors.
1.1.1.1.2 Increase in fire truck accidents
There are not adequate staging areas, nor pre -identified staging
areas for trucks. There is a concern about losing equipment.
1.1.1.1.2.1 Losing of equipment
1.1.1.1.2.1.1 Increasing fire
1.1.1.1.2.1.1.1 Spreading of fire
1.1.1.1.3 Delay in obtaining other equipment
1.1.1.1.3.1 Deplete equipment in other towns
This is a general situation county -wide.
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1.1.1.1.3.1.1 Losing of firefighting protection
1.1.1.1.3.2 Fire fighters cannot respond to other fires
1 1.1.1.3.3 Difficulties in using other station services
1.1.1.1.4 Long supply line for support
Having to bring own water and equipment in This is a problem
everywhere in the county outside of the district, except Thompson
has its own water supply.
1.1.1.1.5 Poor radio communications link
Westwater and Hwy 128 are major problem, as is Willow Basin.
Recommendation: Difficult place to put In a repeater. There may bo
no solution. Be aware and make it a part of your pan
1.1.1.1.6 Large area of coverage inadequate service
1.1.1.1.7 Lack of telephone communication
About parallels, radio problems See above.
Recommendation: No soluhon Be aware of poor communications
and make it be a part of your plan.
1.1.1.2 Poor access into URWIN Community
Willow Basin is considered the worst with steep, narrow, and windy
roads Sand Flats Is similar. Dolores Triangle in areas also has poor
access.
The access problems are mainly in the Wetlands,because their Is no
access.
1.1.1.2.1 Curious people blocking access:
1.1.1.2.2 Need for air operations
Thls depends on the value at risk They would call In air operations
for the Willow Basin area and Wilson Mesa and the Dolores Tnangle.
It may also be called In for the Wetlands area if the state would fund
the alydrops.
1.1.1.2.3 Damaging firefighting equipment
1.1.1.2.4 Delaying access for firefighters
1.1.1.2.E Not reaching all structure fires
1.1.1.2.6 Not reaching all vegetation fires
1.1.1.2.7 Not using best firefighting equipment
1.1.1.2.8 Lack of retreat for firefighters
Willow Basin Is of concem, mainly getting people and equipment Into
places where they should not be There are red rack and green rock.
Some places cannot be saved Some homes are built In difficult
places There are places where we will not allow people to be
trapped
The Wetlands would only be fought from Its penmeters.
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1.1.1.2.9 Lack of retreat for equipment
1.1.1.2.10 Not having access to the area
1.1.1.2.11 Delay evacuation efforts
1.1.1.2.12 Increase evacuation difficulty
Willow Basin is of concern. it must be a self evacuation. Has narrow
accesses. Law enforcement must be involved with a plan in place.
There is very poor communication with these people. No direct lines
into this area.
Recommendation: Need a pre -initial atack plan and have the
agencies involved be aware of the problem with communication.
1.1.1.2.13 Public entrapment
The risk is about medium, at least, if not high.
Recommendation: Make the residents be aware. They claim they
are aware, but if the fire starts then they act as if not aware. There
should be a documented history of informing them of the threat and
risk and of evacuation needs.
1.1.1.3 Combustible exteriors
General conddion In all URWIN areas.
Recommendation: There appears to be no solution. The other fuels
should be kept clear, having defensible space, and metal roofs. This can
be done through education.
Recommendation: Educate residents using Urwin and Wufi and other
methods.
Recommendation: Educate budding officials in URWIN mitigation, so
that they not only know the code but also the other measures, as well.
1.1.1.3.1 Premature spotting
1.1.1.3.2 Structure fires
1.1.1.3.3 Hazardous materials involvement
Every fire is a hazardous materials Incident until proven otherwise.
This is a hopeless situation to deal with.There is no
recommendation. Prospectors with mercury and cyanide are
hazards. Illegal materials are Doug Squires job. This area is similar
to other communities, except maybe for prospecting equipment
1.1.1.3.3.1 Ammunition explosion
There are no coded or brdinanoes: In the fire code there is a
control, but it Is impossible to enforce. Some things that are legal,
such as five gallon cans of propane are legal
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1.1.1.3.3.2 Illegal drugs
There are some labs present. They can be present. This is an
awareness for the firefighters.
1.1.1.3.13 Pesticides
1.1.1.3.3.4 Gasoline
1.1.1.3.3.6 Petrochemicals
1.1.1.3.3.6 Fuels
1.1.1.3.4 Generation of heat, flames, and sparks
1.1.1.3.6 Providing fuel for fire
1.1.1.3.6 Increased loss of property
1.1.1.3.6.1 Increased loss of structures
1.1.1.4 Combustible roof materials
1.1.1.4.1 Need for air operations
Yes, due to single access.
1.1.1.4.2 Premature spotting
1.1.1.4.2.1 Increased spread
1.1.1.4.3 Structure fires
1.1.1.4.4 Generation of heat, flames, and sparks
1.1.1.4.6 Providing fuel for fire
1.1.1.4.6 Collapsing roofs
1.1.1.4.6.1 Threat to firefighters
1.1.1.4.6.2 Threat to residents
1.1.1.4.7 Residents entrapped
1.1.1.5 Hazardous materials
1.1.1.5.1 Explosive Materials
1.1.1.6.2 Fuming materials
1.1.1.6 inadequate defensible space
1.1.1.6.1 Need for air operations
1.1.1.6.1.1 Premature conflagration
1.1.1.6.1.2 Structure fires
1.1.1.6.1.3 Generation of heat, flames, and sparks
1.1.1.6.1.4 Losing structures to fire
1.1.1.6.1.6 Accelerates rate of bum
1.1.1.6.1.6 Providing fuel for uphill burn
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1.1.1.6.1.7 Providing fuel for ladder effect
1.1.1.6.1.8 Threat to firefighter from heat, flame, and smoke
1.1.1.6.1.9 Threat to resident from heat, flame, and smoke
1.1.1.6.1.10 Restricted retreat for firefighter
1.1.1.6.1.11 Restricted retreat for resident
1.1.1.6.1.12 Vegetative cover damage
1.1.1.6.1.12.1 Flooding and slides
1.1.1.6.1.12.2 Lost aesthetics
1.1.1.7 Homes on slopes
Willow Basin has many homes on steep slopes.
1.1.1.7.1 Need for air operations
1.1.1.7.2 Premature conflagration
1.1.1.7.3 Providing fuel for uphill burn
1.1.1.7.4 Generating heat, flames, and sparks
1.1.1.7.6 Increasing probability of of losing structures
1.1.1.7.6 Increasing rate of spreading
1.1.1.7.7 Poor access
1.1.1.7.8 Inadequate water supply
1.1.1.7.9 Increasing chance of losing power lines
1.1.1.7.10 Increased chance of materials rolling downslope
1.1.1.7.11 Increased chance of flaming debris rolling downslope
1.1.1.7.12 Preheating of unstop* fuel
1.1.1.8 Carelessness of residents
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Recommendation: Publicity is a main recommendation. The window of
opportunity must be used, when there is much publicity.
Recommendation: Create a second children's program, Urwin and Wufl
II, the dangers of starting small localized fires.
Recommendation: When going to schools, besides talking structure
fires also include URWIN flre fighters.
1.1.1.8.1 People hampering firefighters
1.1.1.8.2 Hampering evacuation process
1.1.1.8.3 Endangering themselves and others
1.1.1.8.4 Start fires In interface, structures, or vegetation
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1.1.1.8.5 Increase loss of property and structures
1.1.1.9 Propane and other fuel tanks
State fire code recommends 5 - 10 feet The National Fire Academy
recommends 30 feet Unvin and Wufi recommend 30 feet.
Recommendation Place Urwin and Wufi into area URWIN homes
1.1.1.9.1 Propane and fuel leaks
1.1.1.9.2 Propane and fuel explosion
1.1.1.9.3 Restricted access
1.1.1.9.4 RestNcted structure firefighting
1.1.1.9.6 Taking additional manpower
1.1.1.9.6 Blowing flaming debris and sparks to structure
1.1.1.10 Adjacent users ofwildlands
1.1.1.10.1 Need for air operations
There are many recreational users here and this creates a higher
than normal fire threat from them. Also there is a greater threat to the
users.
1.1.1,10.1.1 People hampering firefighters
1.1.1.10.1.2 People hampering evacuation process
1.1.1.10.1.3 Involvement of hazardous materials
1.1.1.10.1.4 Diluting resources In main area
1.1.1.10.1.5 Start fires that threaten URWIN community
1.1.1.10.1.6 Endangering themselves and others
1.1.1.10.1.7 Provide fuel to carry fire Into URWIN area
1.1.1.11 Natural gas lines
Northwest and Mapco and Amencan Pipeline Company all run through
Moab. These lines also run through URWIN areas, as well. North end of
Book Cliffs and Westwater and Cisco and Crescent and Thompson and
the south end of the county district, including through the Wetlands
1.1.1.11.1 Gas leaps
1.1.1.11.2 Gas explosions
1.1.1.11.3 Restricted access
1.1.1.11.4 Taking additional manpower
1.1.1.11.5 Utility workers in area
1.1.1.11.5.1 Endangering utility peopte
1.1.1.11.6 Endangering firefighters
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1.1.1.11.7 Endangering residents
1.1.1.12 Petroleum product pipeline
1.1.1.13 Crude oil pipelines
Mapco has "something"
1.1.1.14 Power lines
1.1.1.14.1 Threat to air operations
1.1.1.14.2 Electrical ignition source
1.1.1.14.3 Hazardous materials sources
1.1.1.14.3.1 Power transformers
1.1.1.14.3.1.1 PCBs
1.1.1.14.4 Electrocution of residents
1.1.1.14.5 Electrocution of firefighters
1.1.1.14.6 Shutting off electric water pumps
1.1.1.14.7 Restricting access for firefighters
1.1.1.14.E Restricting evacuation
1.1.1.14.9 Electrocution of animals
1.1.1.14.10 utility workers present
1.1.1.14.11 Dead wires on the ground
1.1.1.14.12 Losing communications and telephone problems
1.1.1.14.13 Losing home power
1.1.1.14.13.1 Losing home lighting
1.1.1.14.14 Restrict firefighting tactics
1.1.1.15 Inadequate manpower
1.1.1.15.1 Use Improperly trained firefighters
1.1.1.15.1.1 Accidents in fighting fire
1.1.1.15.1.1.1 Liability law suites
1.1.1.15.1.1.2 Depletion of manpower due to rescue
1.1.1.15.1.2 Strain on available firefighters
1.1.1.16 Inadequate or Improper water supply
1.1.1.16.1 Need for air operations
1.1.1.16.1.1 Increasing risk and accidents
1.1.1.16.1.1.1 Endangering rescuers
1.1.1.16.2 Cannot fight all structure fires
1.1.1.16.2.1 Fire spreads
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1.1.1.16.2.1.1 increasing threat to residents
1.1.1.16.2.1.2 Increasing property loss
1.1.1.16.3 Cannot fight all vegetation fires
1.1.1.16.3.1 Losing area aesthetics
1.1.1.16.3.1.1 decreasing development
1.1.1.16.3.1.1.1 decreasing tax base
1.1.1.16.3.1.2 decreasing home sales
1.1.1.16.3.1.3 decreasing property sales
1.1.1.16.3.1.4 Decreasing tourism
1.1.1.16.4 Cannot use all pumping equipment
1.1.1.18.4.1 Fire spreads
1.1.1.16.4.1.1 Increasing property loss
1.1.1.18.4.1.2 Increasing threat to life
1.1.1.16.6 Placing firefighters In danger
1.1.1.16.6.1 Increasing threat to rescuers
1.1.1.16.6.1.1 decreasing firefighting manpower
1.1.1.16.5.1.1.1 Fire spreads
1.1.1.18.5.1.1.1.1 Increasing threat to life
1.1.1.16.5.1.1.1.2 Increasing threat to property
1.1.1.16.6 Requiring shuttle system
1.1.1.16.6.1 Diluting of resources
1.1.1.16.6.1.1 Loss of transportation
1.1.1.16.6.1.1.1 Causing Increase in response tre
1.1.1.18.6.1.1.1.1 Increasing need for traffic control
1.1.1.16.6.1.2 Loss in response time
1.1.1.17 Damaged natural beauty
1.1.1.17.1 Losing development appeal
1.1.1.17.1.1 Decreasing tax base
1.1.1.17.2 Losing seasonal tourism
1.1.1.17.2.1 Losing tourist revenue
1.1.1.17.2.1.1 Losing area business
1.1.1.17.3 Losing tax base
1.1.1.17.3.1 Losing funds and other programs
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