Birch Bay Comprehensive Stormwater Plan, Projects Recommended for CIP Inclusion

PREPARED FOR:	Roland Middleton, Whatcom County
PREPARED BY:	Bill Derry, CH2M HILL Amy Engstrom, CH2M HILL
DATE:	date \@ "MMMM d, yyyy"April 14, 2006

Introduction

This memorandum is one element of an overall comprehensive stormwater plan for the watersheds of Birch Bay. Birch Bay is a rapidly growing community that is experiencing increasing flooding and erosion, declining water quality and loss of aquatic habitat. Historically, Birch Bay has been primarily a recreational beach community. The citizens of Birch Bay completed a comprehensive land use plan that called for low impact development and a stormwater plan to protect their lifestyle and aquatic resources while accommodating the anticipated growth. This plan will recommend measures to do that.

Water quantity, water quality, and habitat issues identified within Birch Bay were outlined and prioritized in Chapter __ (IDENTIFIED PROBLEMS AND ISSUES CHAPTER) of the Birch Bay Stormwater Plan. This prioritization of problems was performed using criteria reflecting the goals and action items outlined in both the Whatcom County Comprehensive Plan and the Birch Bay Sub‑Area Plan. Several of these identified problems can be addressed with projects suitable for the Whatcom County CIP.

This memorandum identifies and prioritizes projects for inclusion in a 6-year stormwater CIP for Birch Bay. Estimated capital costs, maintenance costs, and potential funding sources are outlined for each proposed project. Attached Fact Sheets provide detailed information for each proposed CIP project.

Identification and Prioritization of Proposed CIP Projects

Potential solutions have been identified for each water quantity, water quality, and habitat problem identified in the Birch Bay area. Chapter __ (ALTERNATIVES CHAPTER) of the Birch Bay Stormwater Plan describes what type(s) of solution(s) would be appropriate for each identified problem. Solutions can range from structural solutions such as enlarging or  re-routing a drainage pipe to non-structural such as increasing maintenance or public education. Problems can be addressed by several types of solutions, often by combinations of solutions. Twelve of the identified issues in Birch Bay call for some degree of capital project as a solution, either as a stand-alone CIP project or paired with a non-structural solution such as increased maintenance, public education, inspection or enforcement. Table 1 in this memorandum contains a listing of the twelve identified problems that may be addressed with a CIP project.

Not all of the problems identified in this process can or should be addressed. One problem, erosion of the Birch Bay Drive road surface, will be addressed in a future project already in the planning stages. Therefore, this problem was eliminated from this CIP prioritization analysis. Of the remaining problems identified as having CIP solutions, five were ranked in the bottom half of all the forty-one water quality, water quantity, and habitat problems identified initially. These problems with rankings in the bottom half are not further analyzed here. These problems were rated lower than other problems, indicating they are relatively less important than other problems. In addition, many of these problems can be addressed by programmatic solutions such as increased O&M or more frequent inspection and enforcement rather than CIP projects. The proposed CIP projects were then ranked according to their original problem ranking.Table 1 indicates the problems and corresponding projects.

Details of Proposed CIP Projects

This section contains a brief description of the identified problem and a corresponding description of a potential solution. Each proposed CIP project is explained in greater detail in the attached Fact Sheets, one for each proposed project. Figure 1 shows the locations of each project proposed for the 6-year Whatcom County CIP.

1.                              Birch Bay Drive Roadway Improvements

As mentioned above, this problem will be addressed by an existing project that is underway. Therefore, additional description or analysis is not provided here.

2.                              Drainage Improvements, Cottonwood Neighborhood

The runoff from a large area flows through a culvert under Anderson Road, in an open channel through the county-owned park, then in a pipe and through a structure leading to two outfalls discharging to Birch Bay at Cottonwood Beach. The structure that exists at the beginning of the two outfall structures is located behind the home at 8212 Birch Bay Drive. The pipe leading to the structure is possibly located underneath a home along Cedar east of Birch Bay Drive.

The runoff from this area often overwhelms the system at the diversion structure at the top of the two outfall pipes. This increased runoff.  Movement of sand along the beach periodically blocks the outlet and causes backwater conditions in the pipes.  This condition is made worse under high tide and high landward wind conditions. As development continues in the upper portion of the watershed, runoff volumes and peak flowrates may increase. Therefore, this problem will only get worse with time.

The yard at 8212 Birch Bay Drive periodically floods.  This may be because of back-ups in the pipe system described above.  It also may be because surface water from the yard has no way to enter the pipe system and no positive outlet.

Additional analysis of the system and the flows (model) is needed followed by design and construction of improvements.

3.                              Drainage Improvements, Shintaffer Road at Richmond Park

A large portion of the runoff conveyed in the ditches alongside Shintaffer Road appears to have been diverted or otherwise re-routed to the west away from Shintaffer Road into a pipe system with two 90-degree bends near the northern extent of the Richmond Park subdivision. Then runoff is then conveyed in ditches and culverts through the subdivision before discharging to an open channel / creek system and flowing to the south towards Birch Bay.

At the location of the flow diversion into the pipe, runoff backs up behind the seemingly undersized culvert system in the subdivision. Yards and driveways are inundated with water. As development is planned for the open area to the north of the existing Richmond Park subdivision, this drainage problem has the potential to become worse.

The roadside ditches along Shintaffer Road are large and appear to have been designed to convey large amounts of flow. The ditches to the south of the pipe diversion appear to be sized to handle the flow that is diverted through the subdivision. The location of flooding indicates that the pipe under the most upstream driveway is too small and should be enlarged.  Analysis of the flows (model) followed by design and construction of improvements is needed.

4.                              Lower Terrell Creek Reconfiguration; Low Dissolved Oxygen

At one time, Terrell Creek followed a natural path through the area. It is natural for a coastal stream to move in the direction of long-shore drift. Then, occasionally during a large storm event, the creek will cut through to a new, more direct outlet to salt water and the drift process starts over. As development in Birch Bay proceeded, sections of Terrell Creek were confined and the creek no longer was allowed to find a natural course. Current patterns of development permanently set the location of Terrell Creek. Currently, Terrell Creek follows the beach shoreline from the State Park to its outlet near Lora Lane.

This entire stretch along with a large portion of the creek within the State Park is tidally influenced. The Terrell Creek marsh (within Birch Bay State Park) is one of the few remaining saltwater/freshwater estuaries in northern Puget Sound. The north end of Birch Bay State Park is a natural game sanctuary providing refuge for smaller birds, migratory waterfowl, American Bald Eagles and the Great Blue Heron.

The lower confined reaches of Terrell Creek are affected by tidal changes that may cause stagnant conditions under periods of high tide. Therefore, the reaches of Terrell Creek between Birch Bay State Park and the outlet of the creek into Birch Bay have had measured low dissolved oxygen levels and higher temperatures.  This has led to fish kills.

Potential solutions might include reducing sources of nutrients or BOD, shading the creek or relocating the mouth of the creek to provide a more direct path to the bay. The benefits of a more direct pathway for Terrell Creek would have to be weighed against current habitat use and other factors.  This project would first require a feasibility study.

5.                              Drainage Improvements, Birch Point, Various Locations

The natural hydrology in the Birch Point area has been altered such that now stormwater runoff is conveyed through culverts and ditches. Construction of roadways and roadside ditches has altered the surface and sub-surface flow throughout Birch Point. Sub-surface flow in the upper portion of soil is intercepted by roadside ditches and is conveyed more quickly and in more concentrated amounts than if the roadway and roadside ditches had not been there. By intercepting horizontal flow and removing water from shallow soils, roadside ditches reduce the amount of water moving across private properties toward the bluff. Surface flow is conveyed in cross-culverts and roadside ditches then flows towards Birch Bay in concentrated flow streams that may contribute to erosion and stability problems at the point of discharge. Ditches also accelerate velocities of runoff because they are straight and relatively smooth. Ditch construction has channelized the system and promoted higher runoff velocities and greater volumes of runoff.

The sub-surface geology of the area consists of clay and hard-packed marine sediments. Infiltration capacity is limited because of this. Drainage issues are therefore more pronounced because the soil is less forgiving. This is true throughout the Birch Bay area but particularly in the northern half where marine soils predominate.

Loss of vegetation has increased volumes of runoff and peak flows.

Problems identified in the Birch Point area include:

·         Oertel Drive ditch overwhelmed, loss of capacity due to accumulated material; residents have cut paths for water access, etc

·         8621 Semiahmoo Drive drainage ditches overwhelmed, low point in roadway

·         Normar Place, erosion of ditch and surrounding material during storm, plugged up outlet and overwhelmed system

·         Localized road flooding at the Semiahmoo Drive and Birch Point Road intersection.

 

Several of these problem spots may be addressed with construction projects such as drainage re-routes and capacity increases. However, these capital project solutions should be performed concurrently with public education on proper drainage techniques, stricter requirements on addition of impervious surface and tree removal, and the implementation of projects such as LID that have the potential for limiting runoff.

David Evans and Associates is presently investigating each of the drainage courses from the Trillium property to the beach to identify potential capacity, erosion and slope stability issues. That information will be incorporated when it becomes available.

This capital project should also be coordinated with any programmatic or planning-level solution proposed for the erosion and stability issues around Birch Point.

6.                              Terrell Creek Culvert at Grandview Road

The Grandview Road crossing of Terrell Creek is currently a fish passage barrier under low-flow conditions. [The culvert at Blaine Road also is a fish passage barrier but is currently slated for replacement by the Washington Department of Transportation.] The culvert at Grandview Road is situated high enough above the creek bed that any fish passage is impossible.

This culvert would have to be replaced or the channel downstream from the culvert would have to be built up in elevation to allow for fish passage through the existing culvert. Project elements may include a series of weirs downstream of the culvert plus the installation of a fish-friendly culvert at the road crossing.

7.                              Drainage Improvements, Rogers Slough at Birch Point Road

Drainage ditches discharging to Rogers Slough back up behind the tide gate under high tide and/or wet weather conditions. When these ditches overflow, backyard flooding occurs in the homes within Birch Bay Village that have backyards along Birch Point Road. Ditches also back up along the north side of Birch Point Road.

Much of this area may be at or just above high tide level. During wet periods, runoff will backup behind the existing tide gate until the tide recedes and this runoff can discharge through the gate. However, this drainage is prevented by either a non-functioning tide gate, an excess of runoff into the system, or lack of maintenance of the tide gate. Accumulated material within Rogers Slough also may prevent adequate drainage from the system. Note that the flooded areas are low and historically are likely to have been wet even before homes and roads were built in the area. Therefore, potential solutions may include improvements to the drainage system, improved maintenance to remove debris, filling flooded yards or tolerating temporary flooding.  Further analysis is needed. It may be appropriate to prevent further home construction in wet areas.

Birch Bay Village representatives have proposed a culvert re-route along Birch Point Road under the Birch Point Loop to alleviate flooding. As development continues in the upper portions of the Rogers Slough drainage area,

This capital project should be coordinated with updated Operations and Maintenance (O&M) procedures and plans associated with tide gates and tide gate operation. In addition, any updates to planning requirements and requirements on LID and other source control should be made with this problem/project in mind.