Approved Meeting Minutes
Herring River Restoration Committee (HRRC)
Cape Cod National Seashore Headquarters
Wellfleet, MA
November 29, 2012
9:30 am-5:00 pm
Members Present: Tim Smith, Eric Derleth, Hunt Durey, Steve Spear, Steve Block,
Others Present: Margo Fenn, John Portnoy, Don Palladino, Nils Wiberg, Peter Boyle, Dean Audet, Kirk Bosma
Overview and Meeting Goals: Nils Wiberg of Fuss & O’Neill reviewed the meeting agenda with the Committee. He noted that the group needed to review the three selected dike design alternatives and the updated design criteria and select a recommended alternative in preparation for meeting with Wellfleet town officials on December 12, 2012. Following selection of a recommended structure design, Fuss and O’Neill will develop a comparative matrix summarizing its evaluation of the tide gate alternatives to facilitate HRRC’s review and selection of a preferred gate configuration.
Control Structure Gate Alternatives: Peter Boyle presented information on four different types of tide gates: Slide gates, combination slide-flap gates, dual-leaf slide gates, and inverted weir stop logs. Independent flap gates were also noted as an additional type that could be used in combination of either of the above types to promote one-way flow into or out of the system. These tide gate options could be used in combination with any of the three proposed dike designs discussed at the October meeting but for purposes of analysis, Fuss & O’Neill prepared the following example pairings to illustrate how the gate configurations could be incorporated into a structural layout:
-Three Sided Pre-cast Concrete Box Culvert with Slide Gates
-Four Sided Pre-cast Concrete Box Culvert with Dual Leaf Slide Gates
-Multiple-Span Pre-stressed Pre-cast Concrete Box Beam Bridge with Inverted Weir Stop Logs
The Committee discussed the advantages and disadvantages of different types of tide gates. Peter Boyle noted that there are aesthetic issues with rising stem tide gates as the stems would protrude several feet above the bridge/dike deck in any gate position, for as long as the gates are in place, and the gate panels would extend above the deck when the gates are raised. In addition, depending on the required operation and maintenance requirements for the gates, the gate support frames may protrude above the bridge/dike deck. Dual leaf slide gates are less obtrusive due to the fact that the gate panels could remain below the bridge deck, but even these gates would have a stem extending above the deck similar to the slide gate. It was noted that the stems are often equipped with weather-protective stem covers, and the Committee noted
that the covers could be disguised as flagpoles. Kirk Bosma commented that there might be times during the adaptive management process when managers will want to let more water out of than into the river; combination slide/flap gates or provision of additional stand-alone flap gates could allow for this. Hunt Durey also noted that there might be times when managers would want to keep the flap gates shut to allow sediment to settle out upstream of the dike. Regardless of the type of gate selected, the Committee agreed that it is important to be able to close the gates, if necessary.
The cost of tide gates varies widely with the weir stop logs being the least expensive option and the dual leaf slide gates the most expensive. Kirk Bosma noted that it might make sense to use more than one kind of gate within the bridge/dike structure, having some bays with fixed panels, some bays with slide panels and some with stop logs, for example. This approach could provide maximum management flexibility.
Structural Alternatives: Peter Boyle reviewed the comparative advantages and disadvantages of the three different structure designs as follows:
Four Sided Pre-cast Concrete Box Culvert:
-Highest construction cost
-Estimated 8-10 month construction duration
-Concrete floor provides scour protection
-More difficult to inspect and maintain than bridge alternative
-Least conducive to long- term fish and canoe/kayak passage
-Largest structural footprint (196’ length plus 900’ retaining wall)
Three Sided Pre-cast Concrete Box Culvert:
-Intermediate construction cost
-Estimated 7-9 month construction duration (shortest construction period)
-Natural channel bottom – requires scour protection
-Slightly more difficult to inspect and maintain than multiple four sided boxes
-Less conducive to long- term fish and canoe/kayak passage vs. bridge alternative
Pre-cast Concrete Box Beam Bridge:
-Lowest construction cost
-Estimated 10-12 month construction duration (longest construction period)
-Natural channel bottom – requires scour protection
-Easiest to inspect and maintain
-Most conducive to long-term fish and canoe/kayak passage
-Smallest structural footprint
Kirk Bosma commented that a concrete apron or rip-rap would likely be needed for scour protection during the Adaptive Management phase due to high water velocities. He also noted that it might be easier to perform maintenance work on the tide gates if they were located at the end of the culverts rather than internal to the culvert structure. The Committee briefly discussed how construction materials might be brought into the site, noting that truck trips on local roads could be an issue. Barging materials in could be an option, however, the comparative costs would need to be evaluated.
LLP Data: The Committee took a break from the Fuss & O’Neill workshop session midday to discuss mapping of low-lying properties (LLP) with Kirk Bosma. Tim Smith explained the LLP outreach process and reviewed some of the parcel maps and modeling data. Kirk Bosma said that, where available, the sensitive receptor data is the most accurate information to use for specific parcels. Where it is not available, it might be possible to use more detailed topographic elevation data to determine water depths for the different tidal benchmarks. It may be necessary to survey all the properties that could have structural impacts to get a more precise understanding of the impacts.
Tim Smith agreed to work with Kirk Bosma to examine some sample sites in order to fine-tune the information that HRRC can provide to LLP owners.
Gate Operators: Nils Wiberg explained that any of the tide gate alternatives could be operated with either manual or automatic controls. Manual operators are the lowest cost option. They require less maintenance than automatic operators but they require a significant amount of time and labor to use. A tripod drill can be used to reduce time and labor but this has to be done carefully. If not operated properly, the drill can damage the tide gates. Automatic operators are more expensive to buy and to maintain. They require electrical service (or a generator). They are the least labor-intensive to operate and could be monitored and operated remotely.
Roadway Cross-Section and Accessibility Alternatives: Nils Wiberg presented a proposed roadway cross-section showing two 12-foot travel lanes, a 5-foot shoulder on the downstream (harbor) side and a 3-foot shoulder on the upstream side, a 5-foot walkway a 10-foot wide operations/public access area adjacent to the downstream lane, and concrete parapets along both sides of the structure. A retaining wall with a parapet extension would need to be extended along the embankment on either side of the proposed structure to achieve FEMA certification of the dike as a flood control barrier.
Building the walkway from the north end of the bridge to the public parking area would require moving existing guardrails and utility poles and also would require a retaining wall. HRRC members requested that the costs of these elements be estimated separately so that town and NPS officials can evaluate them. Tim Smith noted that there are NPS safety standards that might apply. In fact, the design of the entire structure might need to undergo a Value Assessment if Park Service funds are used for construction.
Tim Smith will check with NPS officials about the requirements for evaluating the structural designs.
Traffic Bypass: Peter Boyle explained the options for managing traffic during the construction period. There are three basic options: Staging construction to allow traffic to continue to use the road during construction, building a temporary bypass bridge, and building an off-site bypass route. Staging construction would significantly increase the construction time period. Building a temporary bypass bridge would be expensive and would likely cause significant environmental impacts. High Toss Road and Duck Harbor Road have been considered as a bypass route. This would create a four and a half-mile detour, and would necessitate widening and improving approximately one and a half miles of Duck Harbor Road, as it is now just a one-lane dirt road with overhanging vegetation. This would cost approximately $200,000 to
$400,000.
Peter Boyle presented another option that Fuss & O’Neill has considered, which would be to build a temporary bridge on the existing dike to divert traffic during construction. This would only work cost-effectively with the three-sided bridge and the box beam bridge designs. He explained the construction sequence under this option. HRRC members were supportive of this option as it could achieve several objectives including limiting new wetland disturbance, reducing costs and eliminating the need for a costly and lengthy bypass route. The Committee asked Fuss & O’Neill to develop a cost estimate for this option.
Review of Updated Design Criteria Matrix: The Committee reviewed and discussed the Comparative Constraints Analysis Summary Table included as Attachment C in the Fuss and O’Neill Draft Technical Memorandum. This matrix includes evaluation criteria for the different structure/tide gate alternatives including:
-Natural Resources and Environmental Criteria
-Physical Processes Criteria
-Construction Phase Criteria
-Long-Term Operation and Maintenance Criteria
-Public Use and Enjoyment Criteria
Nils Wiberg explained the scoring and weighting system used in the matrix. The Committee then reviewed each of the criteria and suggested some adjustments to the weighting and scoring, including combining some criteria that were redundant and adding a new item under long-term operation and maintenance criteria to address ease of bypass. Nils Wiberg agreed to revise the matrix to reflect the Committee’s suggestions prior to the December 12, 2012 meeting with Wellfleet town officials.
It was the consensus of the Committee that the best structural option would be the pre-cast concrete box beam bridge. This alternative offers the lowest construction cost, it provides the best conditions for both fish and recreational boat passage, it minimizes environmental disturbance, is more aesthetically pleasing and it offers a simpler method for traffic management during construction. The group acknowledged that box culverts are a more conventional approach for addressing FEMA flood control standards, but the Fuss & O’Neill engineers said that the bridge option could also meet these standards. The Committee had a brief discussion about where in the Herring River system it would make most sense to build FEMA compliant structure(s). Steve Spear suggested that it might be more cost effective to build
FEMA-compliant structures at Mill Creek and Pole Dike Creek rather than at Chequessett Neck Road (CNR). While most of the affected private properties are located in Mill Creek and Upper Pole Dike Creek, only CNR offers the opportunity to provide flood protection for the entire estuary.
Dean Audet suggested that the group consult with the MA State Floodplain Coordinator after the preferred design is selected. The HRRC needs to consult with Wellfleet Town officials and NPS staff before selecting the recommended design.
December Meeting with the Town of Wellfleet: The Committee discussed the upcoming meeting with Wellfleet town officials. The purpose of the meeting is to solicit input on the structural design options for the dike/bridge and tide gates, as well as related public amenities such as fishing/viewing piers, improved parking areas, sidewalks, bike lanes, and/or a canoe/kayak launch. The Committee asked Fuss & O’Neill to prepare a basic presentation on the three structural alternatives and outline some of the key design components such as the parapet/floodwall, public amenities, the different types of operators, the aesthetic differences among the designs and the traffic bypass options. The presentation should review the evaluation criteria and explain the HRRC’s recommended preference for the bridge design.
At the beginning of the meeting, HRRC members will explore how best to coordinate with town and Seashore officials to develop a Memorandum of Understanding (MOU) to guide the Restoration Project through permitting, final engineering design, construction and implementation. This MOU (MOU III) must define roles and responsibilities among the Project proponents including ownership, maintenance, and operations of the tidal control infrastructure. It would be ideal to set up a working group with representatives of the Selectmen from both Wellfleet and Truro, the two Town Managers and Cape Cod National Seashore officials to meet with us on a regular basis during the coming months.
Margo Fenn agreed to draft an email to the Wellfleet Town officials regarding the December 12, 2012 meeting. Fuss & O’Neill agreed to provide some of the key PowerPoint slides describing the structural alternatives to include with that email.
Documents Referred to in the Meeting:
Draft Technical Memorandum-Dike and Control Structure Alternatives Analysis
Herring River Salt Marsh Restoration Project, Fuss & O’Neill, November 2012
Respectfully submitted,
Hillary Greenberg-Lemos
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