HomeMy Public PortalAbout2020 - JC Storm Review of 7-19-20 Event - FINAL REPORT 10-2-20Bartlett
. I West
October 2, 2020
1719 Southridge Drive, Suite 100
Jefferson City, MO 65109
ph (573) 634-3181
www.bartlettwest.com
Mr. Steve Crowell
City Administrator
City of Jefferson
320 E McCarty
Jefferson City, MO 65101
Re: City of Jefferson — Storm Event Review of Flash Flooding July 19, 2020
Dear Mr. Crowell,
As requested, this report describes the initial findings of a cursory review of the flash
flooding that occurred recently on July 19, 2020. The extent of this review is described in
the report and is specific only to four general areas along the Boggs Creek watershed. These
areas are generally described as:
Y Bald Hill/Calvin Lane Area
Y Elm Street Area
Y Christopher Place Area
Y McCarty Street Area
The following report describes the study areas, observations made from site visits and
review of information provided by the City, and a few interviews with City staff and
property owners in the areas. It is important to note that this review was very brief and
limited in scope. Further review and detailed calculations could be provided for further
insight, and this report in no way is any attempt to solve the problems at these locations —
only to review the event, make some observations and serve as a third party assessment of
what happened in that event.
Bartlett & West appreciates the opportunity to serve the City of Jefferson. Please feel free
to contact us with any comments, questions, or concerns. We could expand on these
observations and reviews further if more time is warranted or desired.
Sincerely,
Bob Gilbert, P.E.
Senior Vice President
Attachments
Driving community and industry forward, together.
Study Area and Background
The study areas are along the Boggs Creek Watershed along the same tributary that
experienced a large rainfall on July 19, 2020. Residents and businesses along the tributary
experienced significant structure flooding and expressed their hardships to the City at a Public
Works and Planning Committee meeting on August 13, 2020. At this public meeting, the
property owners described the event and damage experienced and mentioned concerns
related to the maintenance of the open channels (the tributary or creek), culverts, and even
timber that clogged some of the system during the event. This report and its background is only
cursory in nature and is meant to be a third party's observation or review of the event so that
City officials can have another opinion related to the event, potential causes, and specifically
any thoughts related to the capacity of the overall system related to some of the clogs that
occurred and/or any causes of those clogs.
It is important to note that this report was not initiated to find solutions to the problems
encountered — only that it was to review what happened. This report does contain some
information about estimated flows, capacities, and even some conclusions that one might infer
as potential alternatives to be considered for solutions, but let it be clear that the information
provided is very approximated and limited in scope and should not be used to base any
proposed actions without further verification and more detailed study.
The study areas are broken into four distinct places for review. These are as follows and will be
described further in later sections of the report (and shown in Figures 1 and 2):
Y Bald Hill Road/Calvin Lane Area —this area is along two small tributaries of Boggs
Creek that flow from the west/southwest. One tributary flows directly east from
between Lee Street and Cordell Avenue in between two homes along Bald Hill to a
small culvert/inlet to cross Bald Hill Road to the main channel of Boggs Creek behind
the homes along Cardinal Street. The other tributary flows more or less
northeasterly from the Moreland Avenue/Elmerine Avenue neighborhoods and
along Bald Hill Road from the south in mostly wooded areas to cross Bald Hill Road
at Calvin Lane to flow to the same main channel behind the homes along Cardinal
Street.
Y Elm Street Area —this is a limited area of review where homes along Elm Street are
very near the main channel described above, just a little farther downstream from
Bald Hill Road/Calvin Lane Area.
Y Christopher Place Area — Christopher Place is a cul-de-sac area with single family
and multi -family structures where the main channel of Boggs Creek runs parallel to
the street northeasterly before turning east to flow to the McCarty Street culvert.
This is a separate area or neighborhood, but as this report will describe, it is very
much associated with the McCarty Street Area because the backwater from McCarty
Street's culvert appears to be the cause of issues.
Bartlett West Page 1 of 21 September 2020
Y McCarty Street Area — this area contains the commercial and multi -family properties
just upstream of the McCarty Street culvert on the main channel of Boggs Creek. It
appears the main concern or area of review is the culvert capacity of the crossing of
McCarty Street—this is because these properties lie below the elevation of McCarty
Street so they are susceptible to backwater that builds up from the culvert.
Figure 1: Study Areas — Bald Hill Road/Calvin Lane and Elm Street
(Google Earth used for base map)
Bartlett West Page 2 of 21 September 2020
Figure 2: Study Areas — Christopher Place and McCarty Street
(Google Earth used for base map)
Methods and Materials Reviewed
For the purposes of this cursory review, the following methods and materials were used to
develop the findings:
Y Video recording of the Public Works and Planning Committee meeting on August 13,
2020
Y Memo to Council from Matt Morasch prepared for the above public meeting, dated
August 12, 2020
Y "Bald Hill Road Storm Drainage Study" prepared by John Huss, PE with Miller &
Associates dated November 17, 1993
Y A personal interview with City staff (Matt Morasch, David Bange, Don Fontana, and
Ryan Moehlman) on August 26, 2020 to kick off the review
Y Personal interviews or phone conversations with a few property owners (this was very
limited to keep the scope and cost of the study low). The video recording mentioned
above was the primary source of property owner concerns and experiences.
Y Excerpts from the Stormwater Master Plan prepared by Burns & McDonnell, unknown
date
Bartlett West Page 3 of 21 September 2020
Y Emails shared by City staff that were provided to Council, and some associated photos
which I have included where pertinent in this report
Y Site visits, which included photo documentation, and some field measurements with a
tape measure (no field survey was conducted)
Y Google Earth for aerial imagery and some approximate land elevations
Y Rainfall gage data from the gage at Calvin Lane and Hyde Park, provided by City staff for
July 19, 2020
Y Rainfall gage data from an online resource known as "Weather Underground"
(https://www.wunderground.com/dashboard/pws/KMOJEFFE49/graph/2020-07-19/2020-07-
19 dail )
Y Streamstats website for approximations of drainage areas and flows
(https://streamstats.usgs.gov/ss/)
Y Hydraulic Series No. 5 Manual for Hydraulic Design of Highway Culverts charts for
culvert capacities
Y Technical Paper No. 40 Rainfall Frequency Atlas of the United States, US Department of
Commerce, dated May 1961 (TP -40 maps)
Y FEMA's Flood Insurance Rate Map (FIRM) as found in the MidMO GIS Interactive Maps
(https://hazards-
fema.maps.arcgis.com/apps/webappviewer/index.html?id=8bOadb51996444d4879338b5529aa
9cd)
Y FloodFactor website for basic flood risk assessment (https://floodfactor.com/)
Rainfall Event
The rainfall that occurred on July 19, 2020 was intense and was measured by a relatively new
rainfall gage at the Calvin Lane wastewater facility. It is rather uncommon to have a rainfall
gage so close to an area of investigation, so having this gage data is very relevant and useful. In
most cases, after storm events when engineers attempt to develop findings, they must be
approximated from rainfall data far away from the area of interest, relatively speaking. Rainfall
events can vary greatly even over short distances within a community. Therefore, it should be
noted that having this data is extremely helpful and about as accurate as can be done on a post -
storm review.
It should be noted that as a reference, TP -40 maps are a good (although dated) resource for
approximating return intervals for storms. The TP -40 maps only show a maximum storm of 100 -
year return interval on certain periods of time of the rainfall. This is statistically the same as
saying this storm event has a 1% chance of happening in any giving year. So, as a point of
reference, TP -40 maps show the 100 -year rainfall as about 3.4" over a 60 -minute period or
4.2" over a 2 -hour period. The memo to Council from City staff indicated 3.8" over a 2 -hour
period for 100 -year event, which is slightly less rainfall than TP -40 shows, but there are other
reference materials for this statistic and should not be viewed as incorrect, but just that there is
Bartlett West Page 4 of 21 September 2020
a range of data sources for rainfall estimates. So, in other words, the sources of data may range
from 3.8-4.2" of rainfall over a 2 -hour period for a 100 -year or 1% chance event. Likewise,
similar ranges for a 60 -minute storm would also potentially be less than 3.4", but for this
report, TP -40 maps are used as the point of reference.
Rain gage data at Calvin Lane
The rain gage at Calvin Lane records rainfall on 15 -minute increments so that flash flood storms
can be observed or recorded on that time interval. The gage recorded a total of 4.39 inches of
rainfall between the hours of 4:30 PM to 6:00 PM. The gage recorded a total storm from 4:15
PM to 7:00 PM of 4.53 inches. The City staff memo reported a slightly different rainfall total — it
referred to 4.4 inches in 1 hour and 15 minutes. This report assumes that the rain gage has a
"tipping bucket" type of measurement device, so I believe the timeframe has to account for the
15 minutes in the period prior to the start of the rainfall. Hence, my estimate of the same
nearly 4.4 inches is over 1 hour and 30 minutes instead of 1 hour and 15 minutes.
Time Stamp
Inches
7/19/202016:15
0
7/19/202016:30
0.02
7/19/202016:45
0.52
7/19/202017:00
0.72
7/19/202017:15
0.87
7/19/2020 17:30
1
7/19/202017:45
0.88
7/19/202018:00
0.4
7/19/202018:15
0.06
7/19/202018:30
0.03
7/19/202018:45
0.03
177 7/19/202019:00
0
Table 1: Rainfall Gage data — Calvin Lane
It should be noted that the rainfall gage data for the 15 -minute period of 5:15-5:30 PM read "1"
inch. Other readings had two significant digits after the integer. For purposes of this study, I
have assumed the decimals for that period were read ".00" and the spreadsheet truncated
those significant digits. There was no reason to remove that period data from the data set for
two reasons —the 15 -minute periods on either side of this period in question were read as
"0.87" and "0.88" inches, with the peak of the storm happening in the "1" inch reading period.
The second reason is the rainfall gage at the Hyde Park City facility also registered the peak of
the storm during the same exact 15 -minute period at "1.32" inches.
Bartlett West Page 5 of 21 September 2020
It should be noted even with some of the minor issues stated above that this was an EXTREME
event — and verified with a rainfall gage directly at the point of interest. We rarely have source
data this precise and convincing. As compared to the TP -40 maps, one can deduce that a 100 -
year return interval (1% chance storm) would be 3.8" of rainfall in 1 hour and 30 minutes.
This storm was documented at nearly 4.4" in that same time period. More study could be
done to approximate the return interval or % chance of this storm occurring in any given year,
but that was not done for this study. In approximate terms, this storm was roughly 15% more
rainfall than a 100 -year (1% chance) 1 hour and 30 -minute storm.
Weather Underground rain gage data
There are other sources of data nearby, which are more "crowd sourced" in nature, but can
provide some perspective. It should be noted that other sources of rainfall away from the
actual site location should be reviewed with understanding that rainfall can vary greatly over
short distances. However, it is worth mentioning that the event was recorded on a rain gage on
Jennifer Drive in a neighborhood approximately 1.5 miles east of the area of interest. This gage
apparently recorded about 6.3 inches over a 2 -hour period that coincides with the same time
periods as the City gages. Looking at the data from this source over the most intense 1 -hour
and 30 minute timeframe (which matches the City's most intense period approximately)
produced an approximate total of 4.3 inches, which is extremely close to the City gages. We
rarely have such close gage data, so it seems we can have confidence that this event was
EXTREME and has been verified by multiple sources that are not anecdotal in nature. This
rainfall can be seen in Figure 3 below.
6
5
4
3
2
1
0
]A
0 in
= Precip. Accum. Total (in) = Precip. Rate (in)
Figure 3: Rainfall Gage data from "Weather Underground" --Jennifer Drive
Site Observations and Findings
This section of the report will discuss the overall assessment of each area. For the purposes of
brevity and because the issues are more or less the same, the Christopher Place and McCarty
Street areas will be combined.
Bartlett West Page 6 of 21 September 2020
Bald Hill Road/Calvin Lane Area
The Bald Hill Road/Calvin Lane Area appears to have several single-family structures that are
susceptible to flooding upon observation of the site. Solely based on a site observation, it
appears these residences have just been built too low in relation to the creeks and roadways in
the vicinity. There are two tributaries of Boggs Creek that converge essentially just southeast of
the intersection of Bald Hill Road and Cardinal Street. The smaller tributary drains from the
west and enters a small pipe culvert (believed to be a 42" pipe based on the "Bald Hill Road
Storm Drainage Study") between the residences at 1304 and 1310 Bald Hill Road and then exits
to the main channel of Boggs Creek downstream of Bald Hill Road just behind the first
residence on the corner at Bald Hill Road/Cardinal Street. It appears upon observation that both
1304 and 1310 Bald Hill Road are susceptible to flooding. During major storm events, it appears
when the pipe culvert is overwhelmed that the flood would enter Bald Hill Road and flow to the
southeast until it can overtop the road and enter the main channel. However, Bald Hill Road is
superelevated on the curve such that the north curb line looks higher than the south curb line.
This would create more ponding in the roadway before the water could be relieved and
overtop. 1310 Bald Hill Road is somewhat "perched" up a little higher, but its garage door
facing Bald Hill Road is low and could likely flood when Bald Hill Road is being overtopped. 1304
appears to be a little higher than 1310, but also has garage doors into the lower level that could
be compromised during a major event.
The other tributary is larger and drains from the south/southeast and ends up flowing
northeasterly along Calvin Lane before going under Bald Hill Road in a double 9'x4' reinforced
concrete box culvert (RCB). This culvert has a rather low head capability, and outlets to a sharp
left -turn flow path immediately downstream of the RCB because of the high topography and
concrete wall on the east side of Bald Hill Road. These conditions make the capacity of this RCB
rather limited. The downstream turn makes the tailwater condition on the culvert higher than
normal and the upstream side can only build about 1' of head before overtopping the Calvin
Lane/Bald Hill Road intersection and then flowing overland toward the northeast ending up in
the same lowpoint as the earlier smaller tributary discussed above before overtopping Bald Hill
Road to the main channel of Boggs Creek.
The homes near Calvin Lane and Bald Hill Road RCB are rather low in relation to the roadways
and the culvert top. In fact, 1522 Calvin Lane and 1412 Bald Hill Road have depressed driveways
and garages that are lower than Calvin Lane and Bald Hill Road roadways and appear to be a
direct path for water that cannot make its way through the RCB under Bald Hill Road. Without
any other evidence, these residences present to a stormwater engineer as almost certain to
flood and given the age of these structures, it would seem doubtful that these structures have
not flooded several times over their existence. 1410 and 1402 Bald Hill Road are a little more
"perched" up above the neighboring residences, providing them with a little more protection,
but these residences are still close to the lowpoint elevation in Bald Hill Road and most
certainly would have water ponding all around the residence, if not into the low openings, in a
Bartlett West Page 7 of 21 September 2020
major event until the water overtops Bald Hill Road or could recede into the localize storm
sewer system. 1312 Bald Hill Road has a rather low garage opening facing south, and it is likely
a couple of feet lower than 1402 Bald Hill Road. It appears susceptible to the lowpoint ponding
on Bald Hill Road also but might also be influenced by the smaller tributary to the west as well.
Upstream of the RCB, it would also appear 1520 and 1518 Calvin Lane and 1422 Bald Hill Road
would be susceptible to flooding based on their elevations in relation to the RCB and roadways
that are adjacent.
Upon site observation, it would appear there are at least 10 residences on the west side of Bald
Hill Road and north side of Calvin Lane that are at risk of flooding.
As was indicated in the Public Works and Planning Committee meeting on August 13th, the
website referred to as "FloodFactor" presents relative risks for flooding, and this application
lists several of the residences in this report as in possible flood hazard areas. This area is not
within a FEMA floodplain map area, so there are not detailed flood study elevations developed
for this region.
4
a.
Field observations indicate these
residences are at risk of flooding
due to low residence elevations
as compared to storm system
and roadways nearby
La f-acler?da(:
Figure 4: Excerpt map from FloodFactor.com, showing residences at risk of flooding
The "Bald Hill Road Storm Drainage Study" dated November 17, 1993 also comes to similar
conclusions, and even offers little in the way of solutions to the problem due to the extremely
Bartlett West Page 8 of 21 September 2020
low elevations of the residences as compared to the channel and roadways in the area. These
homes were simply just built too low and were built prior to modern storm drainage criteria.
For purposes of this study, a rough estimate of flows and hydraulic capacities were developed
at the Bald Hill Road RCB to verify field observations and personal testimony from the residents.
StreamStats is a USGS website application that provides very quick, rough estimates of drainage
areas and flows. Some of the results are in the Appendix. It is important to note that these
results should not be used for any further analysis or design but was used to gauge
observations. The rough estimate of a 10 -year (10% chance of happening in any given year)
flow was 454 cubic feet per second (cfs) and 100 -year (1% chance) flow was 897 cfs. This
corresponds to a drainage area of about 275 acres. Hydraulic Design Series No. 5 nomographs
were used for box culvert flow capacity estimations and the Bald Hill Road RCB is likely capable
of about 400 cfs capacity, under outlet controlled conditions, before overtopping Calvin Lane
and Bald Hill Road (this is based on only about 1' of head developing on the inlet side of the
RCB). Therefore, this RCB is only capable of carrying something slightly less than a 10 -year
event. This same finding was presented in the "Bald Hill Road Storm Drainage Study", which
used a much more robust methodology to determine the same result. It is common that local
stormwater systems are designed to
carry the 10 -year event with
overtopping occurring beyond that
event. However, once again, the
residences in this area were just built
too low in comparison the adjacent road
and storm system.
There was clear evidence even a month
after the event that the roadway was
overtopped with substantial flow rates. I
observed laid down vegetation and
erosion on the east side of Bald Hill Road
indicating where the flow entered the
main channel.
An additional complication raised by the
residents in this area was the fact that
the RCB was clogged with timber and
debris during the event. Pictures
provided by the City prove that the
north cell of the double cell RCB was
partially clogged with debris. Figure 5
depicts the debris shortly after the
Figure 5: Clogged RCB at Bald Hill/Calvin Ln
Bartlett West Page 9 of 21 September 2020
storm event, and it is estimated that the flow through the north cell was reduced during the
storm by 60-80%. The picture depicts that some area under the debris was still flowing and
operational, and it is common that even with debris, water will find its way through the jam to
some degree. If we assume that 80% of the flow was blocked in the north cell that would
equate to 160 cfs not making it through the culvert (the capacity of the culvert is roughly 200
cfs per cell).
There is no doubt that the clog created a somewhat worse condition than if had not been
clogged. However, this study also tries to estimate roughly how much worse it might have
been. When flows cannot get through the RCB they overtop Calvin Lane/Bald Hill Road at the
intersection and then heads northward until it can overtop Bald Hill Road at the lowpoint. The
lowpoint of Bald Hill Road is approximately 2-3 feet lower than the roadway at the RCB and
approximately 260 feet north of the intersection of Bald Hill Road /Calvin Lane. So, the overflow
of the roadway acts as a "broad -crested weir" that is anywhere from 150' wide to 450' wide,
depending on how deep the water gets over Bald Hill Road. The following Table 2 is a rough
estimation of the weir flow at different elevations, using Google Earth as a source for land
elevations and standard broad -crested weir equations.
Weir Elev (approx.)
Weir Length (ft)
Flow
(cfs)
599.0 (road elev)
0
0
599.5 (6" depth)
150
138
600.0 (12" depth)
300
506
600.5 (18" depth)
400
1453
601.0 (24" depth)
450
2149
Table 2: Bald Hill Road Weir Flow Estimations
Based on these estimations and the rainfall data already presented, one can surmise that even
if the flow through the RCB was maximized (400 cfs) that the runoff from the July 19th event
likely exceeded 900 cfs because it was larger than a 100 -year event, so there was at least 500
cfs going down Bald Hill Road to the overtopping point, and likely more. This would mean there
would be at least 12" of depth over Bald Hill Road. So, if the clog prevented 160 cfs from getting
through the Bald Hill Road RCB that would have to overtop the road in addition. If one ratios
the depth between the 12" and 18" depth of flow over Bald Hill Road, then it becomes obvious
that another 160 cfs travelling across the weir would have been neglible to the overall depth of
flow. As a linear relationship with the weir flow estimations, it would mean about 1 inch more
weir depth for the additional 160 cfs caused by the clog. The reports of flooding from residents
were substantial, and while 1" of deeper flooding is technically worse, it would not have
resulted in whether or not damage would have occurred, according to accounts that were
given.
Bartlett West Page 10 of 21 September 2020
As to the cause of the clog, City staff reported that this kind of timber and debris is common
after large storm events. This is true and reasonable. It is a common occurrence in public
infrastructure, and it's important to relate the size of the storm to this amount of debris. Since
this event appears to be an EXTREME event, it is likely it "picked up" more debris and carried it
downstream to the first major crossing (which Bald Hill Road is for most of this watershed).
Other smaller events just didn't get high enough to suspend or carry the heavier debris, but this
event presumably mobilized a considerable debris load. It's important to note that this 275 acre
drainage area is almost entirely wooded forest -like land, other than the residential lots within
the watershed. A rough estimate is about 70% wooded (191 acres), not counting any wood
located on residential properties.
Some residents reported that the timber and debris were caused by the City because of
material left after the construction on Calvin Lane for the wastewater detention facility. One
resident mentioned "sawcuts" on the timber as a reason to believe that those elements were
manmade problems and blamed the City for these items. I reviewed the photos of the clogged
material and found no real signs of recent sawcuts, and the debris in Figure 5 appears to be
rather decomposed timber. I walked the watershed within the wooded areas and found other
timber and debris that has also been transported to some degree and was hung up on other
natural impediments. This is an indication that timber and debris was certainly travelling during
the event, and there's still more debris that will be released in future storms as well. The walk
in the wooded areas also noted substantial amounts of similar timber and limbs as can be seen
in Figure 5, but just at higher elevations that did not encounter flow and mobilize that debris.
Figure 6, 7 and 8 show some of this material in the watershed upstream of the Bald Hill Road
RCB.
As far as the City's project on
Calvin Lane, I reviewed the
photos provided by the City at
the Public Works and Planning
Committee meeting and also
looked at some historical aerial
photos of the wastewater
facility site (one of which was
during it's construction
showing the site in April of
2019 when it was cleared of
wooded vegetation and was a
disturbed soil surface). I
observed no piles or indication
of timber or limbs in the aerial
photo or construction photos Figure 6: Debris in Watershed upstream of Bald Hill RCB on
that would substantiate a claim September 13, 2020
Bartlett West Page 11 of 21 September 2020
that the clog was caused by materials left by the City or its contractors. Perhaps there could be
some evidence that could be presented that substantiate this claim, but I see no evidence
whatsoever that the clog was caused by the City or its contractor, and in fact, I found
substantial evidence of timber within the 191 acres of wooded areas that would indicate that
clog was a natural occurrence and should serve as evidence that it will continue to be a
challenge. This natural process of forested lands will continue, and it's also important to note
that nearly all of the 191 acres and the tributary are on private properties where the City, nor
any public body has any access or responsibility.
Figure 7: Debris in
Watershed upstream of
Bald Hill RCB on
September 13, 2020
Figure 8: Debris in
Watershed upstream of
Bald Hill RCB on
September 13, 2020
Bartlett `i est Page 12 of 21 September 2020
Other Observations around Bald Hill Road/Calvin Lane
While conducting my site visits, I also observed a couple of potential locations where inflow and
infiltration (1&1) might be entering the City's sanitary sewer system. This is a common
occurrence where stormwater during rain events finds its way into the sanitary system and can
overload the capacity of that system. Some of the resident's stories about this flooding event
referred to backups of the sanitary system into their residences through floor drains and toilets.
This is not surprising considering the size of this event and the reported elevations of flow in
the main channel of Boggs Creek.
There were two possible locations of I&I — one is a small ditch that runs northwesterly in the
rear of a property on 1323 Moreland Avenue that appears to flow over a sanitary sewer
manhole (MH 159). It appears water goes into the manhole at this location and could be
prevented with a relocation of the ditch grading or raising the manhole lid by a couple of feet.
The second potential source was a pipe found exposed in the channel bed of the tributary that
was reviewed. This exposed pipe might have joints that could be allowing some water to
infiltrate the sanitary system. It was between manholes 158 and 157 1 believe, but I also see
that this segment of line was also Cured in Place Pipe (CIPP) lined in recent years, so perhaps
there is no infiltration. I thought it best to point out the exposed pipeline in this area for further
review.
-AL
Figure 9: Possible inflow to Sanitary Sewer at MH 159
Bartlett West Page 13 of 21 September 2020
Figure 10: Exposed pipeline in Tributary of Boggs Creek, believed to be sanitary sewer between
MHs 158 and 157
Elm Street Area
The Elm Street Area is generally the area of homes along Elm Street where the main channel of
Boggs Creek (downstream of the Bald Hill Road/Calvin Lane Areas) is immediately behind the
residences and bends toward the east until it goes under Elm Street and Hwy 50 in a box
culvert. The area is a very confined space for the water to travel — especially at the lower end of
Elm Street where 1414 and 1412 Elm Street residences are built very close to the channel and
the opposite side of the channel is a very steep slope. The channel also makes a fairly sharp
turn toward the east at this location, so momentum for the water during high flows is going to
have the tendency to push more toward these residences.
The review of this area was very limited due to private property access. I contacted both 1414
and 1412 Elm Street property owners, but they were not able or willing to meet with me on
site. The owner at 1414 had concerns related to meeting during the pandemic and 1412 was
planning to meet with me, but later declined due to desire to pursue legal claim with the City.
Therefore, I could only make observations from the Elm Street side of the structures. However,
this area appears to obviously be threatened by flooding, and given the large event that
occurred and was documented with rainfall gages in the watershed, I have little reason
whatsoever to question that these residences were inundated significantly by the main channel
flows. The homes are just simply built too close and too low in relation to the main channel
streambed.
Bartlett `i est Page 14 of 21 September 2020
The only other evidence I saw upon my site visit was a small cluster of concrete and PVC pipe
that was laying the channel just downstream of 1414 Elm Street. It was not large enough in my
opinion to contribute in a major way to the flood impacts but could be removed from the
channel to remove any future opportunity for this concrete mass to collect any further debris.
Using Mid MO GIS website tools, it appears this concrete mass is on property owned by the
State of Missouri.
City staff interviews also resulted in some information about some sanitary sewer lateral
repairs that were conducted by the Missouri State Highway Patrol on their property by a
contractor at the time of the event. The photo in Figure 10A
was provided by the City staff and shows the lateral as it was on
the Friday before the event (July 17, 2020). Figure 10B shows
the approximate location of the repair. It was reported that this
was the condition it was left in for the weekend by the
contractor. Assuming that is correct, this would have resulted in
significant inflow of stormwater into the sanitary sewer.
Downstream of this location (including some of the homes on
Elm Street), the sanitary sewer could have experienced high
flows and surcharging into structures. One of the homeowners
on Christopher Place reported to me that their property first
showed signs of flooding from the sewer backing up, and then
the creek flooded the home secondarily. This presumably was
caused at least in part from the inflows to the sanitary system,
such as this location of the lateral repair.
Figure 108: Lateral location under repair (in blue)
Figure 10A: Lateral in creek
being repaired (July 17, 2020 photo)
Bartlett West Page 15 of 21 September 2020
No further review was conducted for this area because it appeared obvious that any hydrologic
or hydraulic investigations would show several feet or more of inundation in an extreme event.
Further work could be conducted to study this in more depth, but due to the very limited
nature of this review and scope of work, I opted to not expend further effort to prove the
obvious.
Figure 11: Narrow Channel and space for flow behind 1414 Elm Street residence
Bartlett . ■ ■est Page 16 of 21 September 2020
These residences are especially at risk
due to close proximity to the main
• channel, steep slopes on the opposite
• • side of the channel and the turn the
stream makes to the east
•
a
•
m
a
Figure 12: Excerpt map from FloodFactor.com, showing residences at risk of flooding
Figure 13: Concrete mass that could be removed from channel
s
Bartlett West Page 17 of 21 September 2020
Christopher Place/McCarty Street Areas
As discussed earlier in the report, these areas are distinct neighborhoods or areas, but upon
review of the flood event, it appears they are actually more or less affected by the same issue —
the backwater created by the McCarty Street RCB Culvert. This area does have the added
benefit of being along a portion of Boggs Creek that has been studied and published in a FEMA
Flood Insurance Rate Map (FIRM) and as such the properties would be eligible to participate in
the Flood Insurance Program administered by FEMA.
The FIRM indicates the 100 -year floodplain as the "blue" shaded area in Figure 14. This map
indicates that the 100 -year (1% chance) event will pond or pool up behind the roadway, and
more or less completely flow through the RCB (no or only very limited overtopping of the road).
Because the commercial, multi -family and single-family structures within the "blue" areas were
all built below the elevation of McCarty Street, this backwater inundates those structures in an
extreme event. Given that we have observed and recorded rainfall data that shows this event
was in excess of the 100 -year event, it seems clear that these structures would flood if one
were to assume the FIRM and underlying studies are correct.
For purposes of general review, I also conducted rough estimates of the flows and hydraulic
performance of the RCB at McCarty Street. StreamStats was used again to provide a very quick,
rough estimate of drainage area and flows. Some of the results are in the Appendix. It is
important to note that these results should not be used for any further analysis or design but
was used to gauge observations. The rough estimate of a 10 -year (10% chance of happening in
any given year) flow was 753 cfs and 100 -year (1% chance) flow was 1460 cfs. This corresponds
to a drainage area of about 704 acres. Hydraulic Design Series No. 5 nomographs were used for
box culvert flow capacity estimations and the McCarty Street RCB is likely capable of about
1400 to 1550 cfs capacity, under outlet controlled conditions with a range of 5 to 6 feet of head
built up above the RCB barrel, before overtopping McCarty. Therefore, this RCB appears to be
capable of carrying more or less the 100 -year event. This essentially confirms the FIRM within a
foot or so. The Google Earth land elevation on McCarty Street's lowpoint was about elevation
571 and the FIRM shows a flood elevation there of about 572.
Corresponding elevations for the businesses and residences that flooded show significantly
lower land elevations in Google Earth. The automotive repair shop at 1530 E McCarty Street
appears to be at an elevation close to 568 and the multi -family complex at 1516 E McCarty
Street appears to be at an elevation close to 566 to 568 depending on which building you pick.
The elevations at Christopher Place are slightly higher, coming in around 568 to 570, but these
elevations are still below the FIRM flood elevation and it's important to note that as you travel
upstream the flood elevations increase as well. The structures in this backwater footprint
should be EXPECTED to flood again given this data.
Also, it does not appear from City staff interviews, some photos and site observations that the
culvert was blocked or clogged during the event. It appears that it operated as expected.
Bartlett West Page 18 of 21 September 2020
Figure 14: Excerpt of FEMA FIRM near McCarty/Christopher Place
Figure 15: Excerpt map from FloodFoctor.com, showing residences at risk of flooding
Bartlett &, ■ ■est Page 19 of 21 September 2020
Conclusions
The review of the flash flooding event of July 19, 2020 contained in this report was a cursory
review to develop some third -party observations of the event for the City of Jefferson. The
following is a list of overall conclusions:
General
1. The rainfall during the afternoon of July 19th equated to essentially 4.4 inches of rainfall
in 1 hour and 30 minutes. This rainfall is in excess of a 100 -year (1% chance) storm
event; therefore, it was an EXTREME event, unlike any in recent history and perhaps
unlike any since the construction of the buildings or structures. Several property owner
conversations indicated statements such as "this never happened in the past" even for
some owners who have owned the properties in excess of 20 years.
2. It's important to note that because the rainfall was recorded by a rain gage at the site of
interest, that this is not an anecdotal report or testimony of the event — it's supported
by the best possible evidence in a post -storm review.
3. Every structure that flooded or was suspected to flood during this review has been in
place for decades and was built long before modern design criteria that would have
likely prevented the construction of such building so low in relation to the streams or
surrounding roadways.
4. Sanitary Sewer surcharges into residences was also reported. This is common during
large rainfall events, but it appears the open lateral in the creek bottom near the Elm
Street Area was potentially a large contributor to sanitary backups downstream of that
location (Elm Street Area and Christopher Place/McCarty Street Areas included in this
review). From the review conducted, it appears all sanitary sewer backups in these areas
were also inundated by the flood waters. It is possible that some residences
experienced only sanitary sewer backups or only flood waters from the creek, but I am
not aware of any structures that were only flooded by sanitary sewer backups.
Bald Hill Road/Calvin Lane Area
1. The residences along the west side of Bald Hill Road and north side of Calvin Lane are
built at elevations that do not allow proper conveyance of overflows across Bald Hill
Road without inundating the structures to some degree.
2. The Bald Hill Road RCB can carry essentially the 10 -year event with all other floods in
excess of that event have to travel north and east across the roadway.
3. It appears the north cell of the Bald Hill Road RCB was clogged at some point during the
flood event and could have been blocked by about 60-80%. The timber and debris in the
clog appear to be rotting, natural material from the 191 acres of forested drainage area
upstream of the culvert. The Bald Hill Road RCB is the first structure in the system to
catch most of the debris from a flood event in this watershed.
4. Even with the north cell of the Bald Hill Road RCB blocked to 80%, it is estimated that
the additional flow that would have been routed over Bald Hill Road because of this
Bartlett West Page 20 of 21 September 2020
condition would have produced only a negligible increase in flood depths over Bald Hill
Road (on the order of 1" in additional depth).
5. There is no supporting evidence that is known to the reviewer that would indicate that
the City or its contractors left the timber or debris from a recent wastewater
construction site that caused the clogging. The evidence obtained during this review
supports that this clog was a natural occurrence.
6. Due to the comparative elevations of the channel, roadway and residences in this area,
the conclusions within the "Bald Hill Road Storm Drainage Study" indicate that there are
no obvious solutions to completely solve the problem in this area. There are certainly
infrastructure improvements that could help the situation, but the costs of such
improvements might likely exceed the cost of the properties protected, and achieving
flood protection from an extreme event might be infeasible without at least purchase of
some of the properties.
7. There might be some opportunity to reduce I&I in the watershed as indicated in this
report.
Elm Street Area
1. This area has residences that have been built too close and too low in relation to the
adjacent main channel of Boggs Creek, and high/steep slopes on the opposite bank and
a sharp easterly turn in the channel just upstream of these homes exacerbates the
problem.
2. There is a concrete mass within the channel just downstream of 1414 Elm Street that
could be removed to help with future potential clogging.
Christopher Place/McCarty Street Area
1. These areas are combined due to the cause of the flooding — the McCarty Street
elevation and backwater created to pass the flood through the RCB.
2. The FIRM and rough calculations conducted by this review confirm that the backwater
for an event such as the July 19th flood (or even smaller floods such as the 100 -year
event) should be EXPECTED to flood these structures again. The structures described in
this report are just simply constructed at an elevation below the backwater of this
culvert.
Appendix
The appendix follows and has some more supporting material used for the development of the
report. For simplicity, it was not enumerated with page numbers, but generally contains the
following info:
1. StreamStat printouts of the Bald Hill Road and McCarty Street culvert drainage areas
2. Rough Calculations of Hydraulics
3. HDS No. 5 Nomographs used to support Rough Calculations
Bartlett West Page 21 of 21 September 2020
9/14/2020 StreamStats
StreamStats Report -Bald Hill DA
Region ID: MO
Workspace ID: M020200914132508815000
Clicked Point (Latitude, Longitude): 38.55703, -92.16165
Time: 2020-09-14 08:25:27 -0500
k1cclung
Pa rk
J"
Basin Characteristics
Parameter
Code
Parameter Description
Value
Unit
DRNAREA
Area that drains to a point on a stream
0.43
square miles
BSHAPE
Basin Shape Factor for Area
2.93
dimensionless
IMPNLCD01
Percentage of impervious area determined from NLCD
8.03
percent
2001 impervious dataset
Peak -Flow Statistics Parameters[Pealk Rural Statewide Region 1 SIR 2014 5165]
https://streamstats.usgs.gov/ss/ 1/3
9/14/2020
Parameter Code
DRNAREA
BSHAPE
Parameter Name
Drainage Area
Basin Shape Factor
StreamStats
Value Units
0.43 square miles
2.93 dimensionless
Peak -Flow Statistics Parameters[Peak Urban Statewide SIR 2010 5073]
Min Limit Max Limit
0.11 8212.38
2.25 26.59
Parameter Code
Parameter Name
Value
Units
Min Limit
Max Limit
DRNAREA
Drainage Area
0.43
square miles
0.28
189
IMPNLCD01
Percent Impervious NLCD2001
8.03
percent
2.3
46
Peak -Flow Statistics Flow Report[Peak Rural Statewide Region 1 SIR 2014 51 651
PII: Prediction Interval -Lower, Plu: Prediction Interval -Upper, SEp: Standard Error of Prediction, SE
Standard Error (other -- see report)
Statistic
Value
Unit
SEp
2 Year Peak Flood
172
ft"3/s
38.4
5 Year Peak Flood
331
ft"3/s
30.8
10 Year Peak Flood
454
ft^3/s
29.1
25 Year Peak Flood
625
ft^3/s
28.8
50 Year Peak Flood
760
ft^3/s
28.7
100 Year Peak Flood
897
ft"3/s
29.8
200 Year Peak Flood
1030
ft^3/s
31
500 Year Peak Flood
1220
ft^3/s
33.2
Peak -Flow Statistics Flow Report[Peak Urban Statewide SIR 2010 50731
PII: Prediction Interval -Lower, Plu: Prediction Interval -Upper, SEp: Standard Error of Prediction, SE
Standard Error (other -- see report)
Statistic
Value
Unit
PII
Plu
SEp
2 Year Peak Flood
147
ft^3/s
91.5
236
26.7
5 Year Peak Flood
262
ft^3/s
172
400
23.3
10 Year Peak Flood
353
ft^3/s
237
526
22.1
25 Year Peak Flood
469
ft^3/s
315
697
22.1
50 Year Peak Flood
575
ft"3/s
377
876
23.3
100 Year Peak Flood
675
ft^3/s
424
1070
25.6
500 Year Peak Flood
941
ft"3/s
509
1740
35.2
https://streamstats.usgs.gov/ss/ 2/3
9/14/2020
StreamStats
Peak -Flow Statistics Citations
Southard, R.E.,2010, Estimation of the Magnituude and Frequency of Floods in Urban
Basins in Missouri: U.S. Geological Survey Scientific Investigations Report 2010-5073, 27
p. (http://pubs.usgs.gov/sir/2010/5073/)
Southard, R.E., and Veilleux, A.G.,2014, Methods for estimating annual exceedance-
probability discharges and largest recorded floods for unregulated streams in rural
Missouri: U.S. Geological Survey Scientific Investigations Report 2014-5165, 39 p.
(http://pubs.usgs.gov/sir/2014/5165/)
USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality
standards relative to the purpose for which the data were collected. Although these data and associated metadata have
been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty
expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems,
nor shall the act of distribution constitute any such warranty.
USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the
software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to
further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the
functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore,
the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not
imply endorsement by the U.S. Government.
Application Version: 4.4.0
https://streamstats.usgs.gov/ss/ 3/3
9/14/2020
StreamStats
StreamStats Report -McCarty Drainage Area
Region ID: MID
Workspace ID: M020200914131519049000
Clicked Point (Latitude, Longitude): 38.56176, -92.15053
Time: 2020-09-14 08:15:38 -0500
IJ
may,
-Z I.J�clung
i�-
F'arE
tly -:lp
4
I� Golf Center
Oak HIII=
Go if enter
Basin Characteristics
Parameter
n Y
'r-
N4
Hd
r 4
�� � s .rte -� tt •' s
Code Parameter Description
DRNAREA Area that drains to a point on a stream
BSHAPE Basin Shape Factor for Area
IMPNLCD01 Percentage of impervious area determined from NLCD
2001 impervious dataset
Peak -Flow Statistics Parameters[Peak Rural Statewide Region 1 SIR 2014 51651
Value Unit
1.1 square miles
3.4 dimensionless
20.4 percent
https://streamstats.usgs.gov/ss/ 1/3
9/14/2020
Parameter Code
DRNAREA
BSHAPE
Parameter Name
Drainage Area
Basin Shape Factor
StreamStats
Value Units
1.1 square miles
3.4 dimensionless
Peak -Flow Statistics Parameters[Peak Urban Statewide SIR 2010 5073]
Min Limit Max Limit
0.11 8212.38
2.25 26.59
Parameter Code
Parameter Name
Value
Units
Min Limit
Max Limit
DRNAREA
Drainage Area
1.1
square miles
0.28
189
IMPNLCD01
Percent Impervious NLCD2001
20.4
percent
2.3
46
Peak -Flow Statistics Flow Report[Peak Rural Statewide Region 1 SIR 2014 51 651
PII: Prediction Interval -Lower, Plu: Prediction Interval -Upper, SEp: Standard Error of Prediction, SE
Standard Error (other -- see report)
Statistic
Value
Unit
SEp
2 Year Peak Flood
295
ft"3/s
38.4
5 Year Peak Flood
555
ft"3/s
30.8
10 Year Peak Flood
753
ft^3/s
29.1
25 Year Peak Flood
1030
ft^3/s
28.8
50 Year Peak Flood
1240
ft^3/s
28.7
100 Year Peak Flood
1460
ft"3/s
29.8
200 Year Peak Flood
1670
ft^3/s
31
500 Year Peak Flood
1970
ft^3/s
33.2
Peak -Flow Statistics Flow Report[Peak Urban Statewide SIR 2010 50731
PII: Prediction Interval -Lower, Plu: Prediction Interval -Upper, SEp: Standard Error of Prediction, SE
Standard Error (other -- see report)
Statistic
Value
Unit
PII
Plu
SEp
2 Year Peak Flood
384
ft^3/s
244
603
26.7
5 Year Peak Flood
624
ft^3/s
421
925
23.3
10 Year Peak Flood
819
ft^3/s
563
1190
22.1
25 Year Peak Flood
1030
ft^3/s
714
1490
22.1
50 Year Peak Flood
1270
ft^3/s
859
1880
23.3
100 Year Peak Flood
1460
ft^3/s
954
2240
25.6
500 Year Peak Flood
2000
ft^3/s
1130
3540
35.2
https://streamstats.usgs.gov/ss/ 2/3
9/14/2020
StreamStats
Peak -Flow Statistics Citations
Southard, R.E.,2010, Estimation of the Magnituude and Frequency of Floods in Urban
Basins in Missouri: U.S. Geological Survey Scientific Investigations Report 2010-5073, 27
p. (http://pubs.usgs.gov/sir/2010/5073/)
Southard, R.E., and Veilleux, A.G.,2014, Methods for estimating annual exceedance-
probability discharges and largest recorded floods for unregulated streams in rural
Missouri: U.S. Geological Survey Scientific Investigations Report 2014-5165, 39 p.
(http://pubs.usgs.gov/sir/2014/5165/)
USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality
standards relative to the purpose for which the data were collected. Although these data and associated metadata have
been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty
expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems,
nor shall the act of distribution constitute any such warranty.
USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the
software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to
further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the
functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore,
the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages
resulting from its authorized or unauthorized use.
USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not
imply endorsement by the U.S. Government.
Application Version: 4.4.0
https://streamstats.usgs.gov/ss/ 3/3