Loading...
HomeMy Public PortalAbout2003 Sea Grant Landings ReportCAPE COD COOPERATIVE EXTENSION Deeds & Probate Building P.O. Box 367 Barnstable, MA 02630-0367 Phone 508-375-6690 Fax 508-362-4518 BREWSTER GC iSERVA.ILN COMMISSION NOG O \./ Sea Grant Woods Hole W000s HOLE OCEANOGRAPHIC INSTITUTION January 15, 2003 Seth Wilkinson, Agent Brewster Conservation Commission Town Hall 2198 Main Street Brewster, MA 02631 RE: Analysis of Storm Damage Potential and ErciSion Control Alternatives for Selected Brewster Town Landings Dear Seth: This report is a follow-up to site visits we conducted to several Brewster Town Landings. Present were you, Town Administrator Charles Sumner, Conservation Commission Chair Steve McKenna, Director of Natural Resources Bob Mant, and DPW Foreman Jim Bearse. The purpose of the site visits were to view shoreline conditions, discuss erosion and storm damage potential at selected landings, and identify possible erosion control and storm damage reduction alternatives for each of the Town Landings visited. A moderate coastal storm occurred shortly before our visits causing wave-induced erosion to several of the landings. This necessitated town action in the form of placing fill at Ellis Landing, the first town landing we visited. Ellis Landing Ellis Landing, located at the end of Ellis Landing Road on Cape Cod Bay, is of considerable concern to the town primarily due to limitations to beach and tidal flat access resulting from relatively frequent storm wave-induced erosion of the access (fill) ramp. The long-term average annual erosion rate at Ellis Landing is approximately —0.66 ft /yr based on several plotted shorelines analyzed between the mid-1800s to 1994. The landing faces north/northwest and is located directly on Cape Cod Bay (Photo 1 aerial photo). Due to the close proximity of the seaward end of the landing to the high water line it will continue to receive relatively frequent storm wave-induced erosion and scarping. This scarping and erosion inhibits beach and tidal flat access, and periodically uncovers a leaching box located under the access (fill) ramp, subjecting it to possible damage. The town is interested in suggestions that may reduce the frequency of storm and erosion ated damage. 1930 1 05 Oyster Pond Road, \IS 42, Woods Hole, MA 025431525 Tel {5081289- • Ex< 15081 457-2172 2 I visited and photographed Ellis Landing on November 1 (see Photos 2 & 4). Note on Photos 2 & 4 (top photos) the close proximity of the high water line (identified by the landward limit of the wrack) to the seaward limit of the access ramp. There is a direct correlation between frequent storm wave-induced erosion with the closeness to high water. On November 1, a small scarp was visible at the seaward end of the access (fill) ramp on the west side of the landing (right side of the fill as shown on Photos 2 & 4) indicating recent wave erosion from a relatively minor storm. Note that only the west portion of the ramp shows erosion or scarp. This is primarily because that section of the ramp (fill) protruded more seaward than the eastern section and was, thus, closer to the high water line and thus wave action. A minor to low-moderate coastal storm occurred between my November 1 visit and our site visit on November 14 that caused considerable erosion, with a scarp approximately 2 —3 feet in elevation at the landing (see Figures 3 & 5). The scarp shown in Figures 3 & 5 cut across the entire landing but the town placed fill across the western section to provide beach and tidal flat access, and to cover an existing storm drain leaching box. Importantly, note that even shortly after the new fill was placed a small wave-induced scarp (erosion of the fill) had already formed. Erosion Control Alternatives The primary goals of the Town at Ellis Landing are to provide continuous access to the beach and tidal flats, and to prevent damage to the leaching box located under the access (fill) ramp. This requires that wave-induced erosion be minimized and, thus, the frequency of adding fill and associated costs also be reduced. Alternative A — Continue to add fill: Historically, the Town simply places/dumps fill at the ramp to create a smooth transition to the beach for pedestrian and vehicle access to the beach and tidal flats. The fill material appears to consist of a mixture of sand, pebble and finer material. While this mixture is not entirely beach compatible, it adds to the stability of the fill for pedestrian and vehicle access down the ramp. This fill is necessitated to compensate for material lost to wave-induced erosion. According to the Town, this has been a frequent and expensive undertaking. A positive contribution of this alternative is that when the fill is eroded from the ramp this material is added to the 'littoral system' (dune, beach and nearshore areas). Alternative B — harden or armor the ramp: The ramp could be re-constructed with concrete or other 'hard' material. If properly designed and embedded deep enough, particularly at the seaward end (i.e. deeper than anticipated storm wave induced lowering of the beach) this would provide stability and potential longevity to the ramp (absent a major storm). However, a hard structure more than likely would increase wave reflection and refraction around the end of the ramp and cause increased 'end scour' or flanking erosion of adjacent areas. For example, increased wave-induced erosion would likely occur to the dune area immediate east of the ramp as a result of wave refraction associated with strong north/northwest winds and waves. 3 Northeast wave reflection would also more than likely cause accelerated erosion of the dunes on the east side. Armoring the fill with gently sloping rip-rap (revetment) could reduce but not eliminate this end-scour or flanking erosion effect but would not necessarily be conducive to easy pedestrian or vehicle access. A hardened structure also may not necessarily be consistent with the performance standards of the Wetlands Protection regulations for dunes or banks at 310 CMR 10.28 & 10.30. Alternative C — Relocate the access ramp further landward: Relocating the ramp/fill further landward would increase its distance from high water and thus would decrease the number of times the ramp is eroded due to storm waves. As a result, the necessity of adding fill should also be reduced, lowering associated costs. This would also necessitate the relocation of the storm drainage system buried under the ramp. This action would require an initial expense but on a long-term basis may be more cost- effective than the current practice. With on-going erosion, the storm-water drainage system located under the access ramp fill will eventually be damaged and need to be addressed, and more than likely will need to be relocated in the future. Discussion With on-going chronic erosion at the site and a potential increase in future storm activity there will more than likely be a concomitant increase in the frequency of adding fill to the ramp and thus increased costs (Alternative A) in the future. Re-constructing and hardening the ramp with concrete or other materials (Alternative B) would reduce erosion of the fill but more then likely would cause increased erosion of adjacent areas (particularly the dune on the east side) due to end scour or flanking erosion. Following a major coastal storm reconstruction expenses would be high. Relocating the ramp further landward (Alternative C) would reduce the frequency of wave interaction and thus erosion of the fill and reduce the frequency of having to add fill. Following moderate coastal storms, however, fill would continue to be required but more than likely at a lower rate. In summary, weighing the pros and cons of the 3 alternatives discussed, relocating the ramp further landward (Alternative C) appears to optimally balance functional, environmental and fiscal components. Breakwater Landing Breakwater Landing is located at the end of Breakwater Road on Cape Cod Bay (Figure 1). I visited Breakwater landings on November 1 and again on November 14 during our site visit (see comparison Photos # 6 & 7). The long-term average annual erosion rate at Breakwater Landing is approximately —0.39 ft/yr, although the erosion rate between 1951 & 1994 appears to have accelerated showing an average annual erosion rate of —2.03 ft/yr. 4 The access ramp to the beach from the parking lot is very gradual and there does not appear to be the problem with erosion/scalping or loss of material of the access/landing due to minor• storms, as is the case with Ellis Landing. This could be due to the elevation of the beach being higher relative to the parking lot. In addition and importantly, the access ramp is further landward in relation to high water, with its seaward end gradually transitioning into the beach and ending in line with the seaward toe of the adjacent dunes. The main problem appears to be erosion of the dune adjacent (west) to the access ramp. Riprap fronts this dune (see Figures 6 & 7). The main question the Town is considering is whether the presence of the riprap fronting the dune is causing accelerated erosion of the dune, and if so, should it be removed. Photo 6 shows the dune and riprap on November 1. Note the dune toe is relatively close to the riprap, approximately 5 feet. A minor coastal storm hit the area shortly before our November 14 site visit and the dune toe was eroded back approximately 15 feet from its November 1 location (see Photo 7). Note in comparing the storm-induced dune scarp location on both sides of the access-way in Photo 7 that the dune scarp appears to be in a similar location. This suggests that the riprap is not necessarily causing increased erosion of the dune itself. However, I did note a small trough immediately landward of the riprap (between the riprap and the dune) that Photo 7 does not show. This indicates that the riprap is causing a slight hydraulic head build-up and causing some increased beach erosion in between the riprap and dune. Photo 8 shows dune erosion on the west side of the dune where there is a gap between the riprap and the adjacent revetment. This could be caused by end scour or pedestrian use from the parking lot. The main adverse impact of the presence of the riprap is that it is preventing aeolian (wind-blown) sand transport from the beach to the dune and thus could severely limit the natural reconstruction of the dune following storms. For this reason, removal of the riprap would be beneficial. I would also suggest closing the pathway or end scour area on the west side of the dune (see Photo 8) and installing snow/sand fencing and/or planting dune grass to assist nature in re-building the dune in this area by trapping wind-blown sand. Alternative In summary, removing the riprap fronting the dune will allow the dune to more quickly and naturally rebuild following storms. Installing sand/snow fencing approximately halfway up the eroded dune on the west side of the riprap leading to the parking lot will assist nature in trapping wind-blown sand and rebuild that portion of the dune quicker. Supplementing planting dune grass in this blowout with the sand/snow fence would be optimum in dune rebuilding. If the blowout on the west end of the dune is being caused by pedestrian access, a `no access dune sign' could be beneficial in educating the public of the sensitive nature of dunes and the beneficial role of dune grass in assisting natural dune rebuilding. WHOI Sea Grant has dune signs and can provide these at no cost. 5 Saints Landing Saints Landing is located at the end of Robbins Hill Road on Cape Cod Bay. The long- term average annual erosion rate for this site based on data from the mid-1800s to 1994 is approximately —0.6 ft/yr. The primary problem at this location is storm water discharge through an existing pipe with the drain beginning in the parking lot and the pipe exiting through the dune face. The runoff/discharge then splashes onto the beach from the elevated pipe exiting through the dime face causing erosion of the dune and beach (see Photos 9A, 9B, 9C). The parking lot is graded such that rain runoff cascades rapidly toward the storm water drain pipe (Photo 10) resulting in velocity runoff cascading through the discharge pipe and onto the beach. The discharge pipe is elevated above beach grade causing considerable erosion of the dune and beach (Figure 9a, b, & c). The outflow is causing not only erosion of the dune but is cutting a gully across the beach to the ocean. When major storms occur the rainfall discharged from the pipe produce maximum scouring of the dune and beach simultaneously with the arrival of large highly erosive storm waves. The gully in the beach caused by the discharge is lower than the adjoining beach grade so the stone wave bore rolls further up the gully, increasing beach and dune erosion. The goal in this situation would be to: 1. Eliminate the parking lot runoff through the pipe by handling the runoff differently; or, 2. Slow the runoff entering and thus exiting the storm water discharge pipe; and, 3. Reduce the elevation of the runoff exiting from the discharge pipe, which will reduce the energy of the discharge runoff hitting the dune & beach. If these are achieved, the beach and dune erosion caused by the discharge will be mitigated, or the energy of cascading waters causing erosion of the beach and dune should concomitantly be reduced thereby minimizing erosion of the dune and beach. Alternatives The construction of a vegetated or gravel-packed leaching trench could be considered in the location of the existing drain (Photo 10). The parking lot could be re-graded to direct runoff towards the leaching trench, although the existing parking lot grade presently appears to direct the runoff towards the drain, so this may not be necessary. This is evident in Photo 9A showing very little, if any, evidence of runoff cascading down the pedestrian access way. This would allow runoff to slowly leach into the ground and avoid the erosive discharge onto the beach and dune. A future problem may be if the vegetated swale or gravel/sand filter beds become clogged with mud, silt or other clogging elements. Alternatively, a connection could be maintained to the existing discharge pipe at the bottom of the vegetated swale or gravel-leaching trench that would be operative during 6 major rainfall events to convey the overflow. This should considerably slow or, if sized appropriately, eliminate the volume and velocity of entering and exiting discharge runoff into and out of the existing pipe. Beach compatible material could be placed to fill the existing dune scarp and beach gully that is presently being caused by the discharged runoff out of the pipe (Photo 9a,b,c). If discharge continues out of the pipe, a splash apron consisting of riprap underlain with filter cloth could further reduce the storm water runoff energy onto the beach, thereby reducing the gulleying effect and erosion of the dune and beach. Some riprap already exists on the beach at the discharge point. The vegetated or gravel leaching trench appears to meet the primary goal of eliminating the runoff from eroding the dune and beach, except perhaps in very large rain fall events. A mechanism to handle the overflow from the vegetated swale or gravel trench in large rainfall events could be constructed. If flow continues out of the pipe, a vertical pipe attached underneath the existing pipe could be added that penetrates below beach grade and thus allows the discharge to infiltrate the beach, rather than fall from the existing elevation. Robbins Hill Beach Robbins Hill Beach Landing is located directly on Cape Cod Bay. The long-term average annual erosion rate at this location is approximately 2 ft/yr based on data analyzed between the mid-1800s to 1994. The main problems here appear to be: 1. Aeolian (wind-blown) sand and overwash sands being deposited into the parking lot; and, 2. It appears that pedestrians find it easier to walk over the dune at the northwest corner of the parking lot to the beach rather than walk the very short distance to the established beach access way causing dune grass destruction. It was evidenced during our site visit that the town was scraping-up the aeolian and over- washed sands from the parking lot and depositing that volume onto the backside and top of the primary dune where the pedestrians were causing dune vegetation impacts by walking over the dune at the northwest corner. This practice of placing the overwash sand from the parking lot back on the foredune seems appropriate. Alternatives: The practice of scraping-up the aeolian and over-washed sand from the parking lot and depositing that volume onto eroded areas of the foredune seems appropriate. A potential way of reducing the volume of aeolian or over-washed sand from entering the parking lot through the pedestrian access-way to the beach (Photo 11) may be to install snow/sand fencing in the middle of the pedestrian access-way. Perhaps 2 rows of staggered fences could be installed, parallel to the dune orientation. Staggering would allow for continued pedestrian access through/around the sand/snow fencing to the beach, 7 while capturing wind-blown and over-washed sand in the location where a foredune would otherwise exist absent pedestrian use. The town of Dennis uses this technique (sand/snow fencing at each public access-way to the beach) during winter months and it is very successful in capturing wind-blown sand: approximately 2-3 vertical feet of aeolian sand has been captured over the past 3 months at Cold Storage Beach access- ways (Photo 12). A consideration of reducing pedestrian access over the dune at the northwest corner of he parking lot may be to simply plant beach grass in bare areas caused by pedestrian use and to install a `no pedestrian access' sign at that location. Sea Grant has such signs (`these dunes aren't made for walking') free of charge. I will send or drop several signs for your consideration. Linnell Landing There are two adjacent pedestrian access-ways to the beach from the Linnell Landing parking lot (Photo 13 & 14). Perhaps one beach access-way is sufficient? Two access- ways invites additional aeolian and storm overwash sand to be carried into the parking lot. Alternatives A. Perhaps one access-way (on the west side) could be closed and the foredune reconstructed with compatible, off-site sand, and planted with beach grass. This should reduce the volume of aeolian and overwash sand into the parking lot. In addition, this may reduce pedestrian impacts to adjacent, private dunes (Photo 15 & 16) by orienting pedestrian away from the adjacent dunes. At present the west side access-way results in pedestrians walking very close to the neighboring dune toe. B. The foredune in both access-way locations could be reconstructed with compatible sand. One restored and planted with beach grass (west side), the other, after sand is deposited, could have a pedestrian dune crossover installed to prevent dune gullying by pedestrian use. I have enclosed literature describing pedestrian crossovers. This should reduce the volume of aeolian and overwash sands entering the parking lot from the beach. Crosby Landing Crosby Landing appears to be in fine shape. The dunes at Crosby Landing are extensive (although low in elevation), and the well-constructed, elevated boardwalk keeps pedestrians from impacting the dunes (Photo 17). The only issue at this beach appears to be the groins (photos 18, 19 & 20). The groins are interfering with natural alongshore sand transport. It is apparent that the net sediment transport is from west to east evident by the fillet (or build-up of sand) on the west side of the groins (see Photos 18 & 19). A couple of groins are causing an offset of the high water line of approximately 45 feet, indicating slight downdrift erosion and updrift accretion. An approximate 3-foot drop of beach grade at the high water line Si cerely, V-- 0 dui Jfrn O'Connell, Coastal Processes Specialist WHOI Sea Grant and Cape Cod Cooperative Extension 8 existed on the downdrift side of the groins, particularly on the east end of the beach. Because of the extensive (although low elevation) dunes, and the Town being the owner of the beach and dune areas, the offsets are not of great concern. If the groins were removed or modified, the beach would even out in its seaward extent, i.e. reducing the beach width on the updrift side of the groin and adding to beach width on the downdrift side. This evening out of beach width would establish more natural conditions and allow sediment transport to continue downdrift unimpeded. It would also facilitate seaward dune growth on the downdrift sides of the groins, but slight erosion of the updrift dunes until natural equilibrium conditions were achieved. On the easternmost groin, however, altering the groin may cause impacts to the existing downdrift saltmarsh by covering the marsh with sand that migrate from the updrift fillet. Notching or slightly unraveling the riprap comprising the groins could be good compromise in closely establishing natural conditions. Perhaps if the riprap is unraveled due to a major storm, the groins could be left in this condition and slowly re-establish natural sand transport and dune equilibrium. Summary In summary, there are actions the town could initiate as described above that could reduce storm and erosion-related impacts to the town landings on Cape Cod Bay. Hopefully, expenditures could be concomitantly reduced as well. I would be happy to go on site again with town officials to further discuss implementation of any of the alternatives described above. I hope this analysis of Brewster's town landing is helpful to the town. Feel free to call me at (508) 289-2993. erp4 31 -t --ra 4r. rter•Vr4r4141::44W4.4.441, 4 4Atot r as. 4 Sighind i ‘t 41.4.4 144. 2.;:4 4 P. ".* -te 7aCi t ite -ri 400.104"Ci t•-• 4—t—r4 Lir .ra • 7te4011. Oh; PC: e-s Ellis Landing, Brewster (Nov 14, 02) ELLIS LANDING Brewster, MA (Nov 14, 2002) 91.191b R cnetytk)s Ly pets. d ct. pro t 11a(viv°0P %lie r°4-"1a BREAKWATER - BREAKWATER LANDING, BREWSTER . (Nov 1, 2002) drainage pipe Itc-ALT: Sr..• e-aftcat;:4 , art: ...it Litre pppro rt: 4 4 -a"":. 4- rt' reiC- r•-• '..t.ttit-4;t:° erer-scarci444,Tc- t.: -°"':/,*-- • -a---;:-.:-..`t :-Ja:r-j'‘. • -/-* :4 c . a '; rt. ...;-,--4.,-......,,,,s-- . -. t , ,-L. ;:tvw,......-4--- • -'ire. ... ' %.:..... P • . 7. -ir . -,_--- .....- tor: ....... 4,m.,,•,,,,g-- it- ..,;:;0,1••• di ._:•• \Ir a -14w 'W. -..•--rs t.,,teril...S. '' s'>41.4..' 41-w reE... il.A.4:0 , 7 - c 4 • . . . it ...1 .e.A '. \ . 4eihr , ,- ;'... Virip4p4Olte le.11"14PaY -. „." • k trijI - .: . 7 . ,... , A MACS • .. l•i• ; ra. .- 'IA r • ci -' ",.-4 L. • 'S, : • -,..L-A-11t; v;0 40 • %gr. ,k IT 104Y-se • vir- wow • BREAKWATER LANDING, BREWSTER (Nov 14, 2002) ?cycvArjo vvrr Al sona I-) A Nbio G) eittuIST? a_. ]3 26 A KPaRTS.R.. git CIASSTE k jivvrv°J,Q vie 4T itiMe Soki:At r:•• . . • • • •-• „Ay,/ • . 4 ri . . .• iiHc.• .r ;111;i1S00.1 tr."•• \‘`‘ , ;1- • • 71d.Lirrav 3E/3 5 01 09`121 ..1•••%.,.‘•• . - . • • • • • ._ F114,...apa Ci.r.:„.9.= • -"r_ • • -;‘, P.rer • ',""a"."-.- ra'a. -"+-PF..”;.71" •••Pit - • uti.." ‘1".? ' 1..":—.s."C"44C,:.4t,-. •C 6. ::'<i • -••;.:erEtclWiAttr5774:. • • I' 11/13/2002 I.W.P. Product 1 Page 1 of 4 Innovative Water Produc LLC Crossovers 6eotextile Dune Crossover Dune crossovers improve beach access by providing a sturdy, yet temporary, walkway over soft sand and dunes. Communities that provide crossovers minimize the environmental degradation that can occur when heavy seasonal traffic tramples dune vegetation. Dune crossovers are easy to install and maintain. Some styles are designed to be easily removed in the off-season. Dune crossovers won't be the source of ?damaging debris during coastal storms. Wheelchair and Vehicle Access ;I.W.P. offers two types of polyethylene pavers that are strong enough for vehicles and perfect for wheel chair access to the beach. They are easy to install and very long lasting. ESSESZIffirea http://www.dunecrossover.corrilprod01.htm I.W.P. Product 1 Page 2 of 4 6eo-Runner Benefits of Dune Crossovers and Access Ways C)Low cost compared to wooden or structural crossovers tO Won't warp or splinter - long lasting! CiGreatly improves walking on soft sand !OProvides access for wheelchairs or maintenance vehicles tO Dune Crossovers can be tailor-made to your specifications. Styles Florida Coast - Our newest Dune Crossover made from one layer of ultra- durable vinyl-coated polyester (see photo above). 27 linear feet by 3 feet wide. Comes with anchoring system. Natural sandy color. The Natural - Pedestrian Dune Crossover made from heavy coconut fibers. The fibers are twisted into strong cords which are woven into a mat suitable for pedestrian traffic. 25 linear feet by 6.5 feet wide. Comes with anchoring system. Color is natural. Geo-Runner - Each panel is 2 ft x 4 ft. (8 square feet) Flexible Paver - Each paver is 0.5 meter X 0.5 meter and interlocks. (2.7 square feet) Pricing http://www.dunecrossover.com/prod01.1fim 11/13/2002 I.W.P. Product 1 Page 3 of 4 Description (Style) SKU # Price Florida Coast DC-006 $145 The Natural DC-004 $95 Geo-Runner DC-005 $14.25 ea. Flexible Paver DC-007 $7.15 ea Information Request Form Select the items that apply, and then let us know how to contact you. n S• end product literature 3 Send samples n Florida Coast r T• he Natural r G• eo-Runner r F• lexible Paver n Have a salesperson contact me Name Title Company/Municipalityl Address E-mail Phone Submit Request I Reset Form http://www.dunecrossover.com/prodOl.htm 11/13/2002 I.W.P. Product 1 Page 4 of4 [Home][Up ] Send mail to Laurieedunecrossover.com with questions or comments about this web site. Copyright 0 2001 Innovative Water Products, LLC http://www.dunecrossover.com/prod01.htm 11/13/2002