DARBY CREEK

Project Name: Bartram Park/Darby Creek Stream Restoration Project Number 2002-PD.16

Client/Project Owner: FEMA and Delaware County.

Project Designer: Delaware County and Delaware Riverkeeper Network.

Technique(s) Demonstrated: Cross Vanes, Boulder Clusters, Spur Dikes

Geographical Location: Bartram Park in Southeastern Pennsylvania.

Geomorphic Setting: The area known today as John Bartram Memorial Park consisted of 38 row houses not more than 5 years ago. In 2000, as a result of the deluge resulting from Hurricane Floyd, the 38 homes along Chestnut Street were razed as part of a regional FEMA buyout.

After the storm, Darby Creek Valley Association and Delaware County Conservation District restored a small portion of this new park area into a natural floodplain and riparian corridor. Work involved regrading and stabilizing 21 linear m (70 linear ft) using biodegradable erosion control fabric and a small riparian buffer planting. Delaware Riverkeeper Network provided some technical assistance in this early restoration work.

At the end of 2002, Delaware County was awarded PA Coastal Zone Management Grant No. 2002 PD.16 to complete restoration efforts in Bartram Park. The original project proposal included:

1. 107 linear m (350 linear ft) of streambank stabilization.

2. 244 linear m (800 linear ft) of riparian buffer restoration.

Performance Period: Construction commenced in February 2004 with bankfull events occurring during summer of 2004.

Project Description: The Bartram Park/Darby Creek Stream Restoration Project improves 427 linear m (1,400 linear ft) of Darby Creek. The focal point of these improvements is the completion of a 34 x 30 x 3 m (110 x 100 x 9 ft) Double Cross Vane that corrects local channel instability. In addition, Boulder Clusters and Stone Deflectors provide fish habitat in areas that have little or no flow variation or cover. And finally, over 244 linear m (800 linear ft) of newly planted riparian buffer provide filtration and habitat for fish and other wildlife along Darby Creek.

Planning and Implementation

After the funding award, Delaware County subcontracted the main project work to Delaware Riverkeeper Network. With design work underway, Delaware Riverkeeper Network began planning the riparian buffer restoration portion of the project. Once the riparian buffer work started, attention refocused to the implementation of the in-stream portion of the project work. With designs in-hand, project partners met to discuss the next phase’s implementation needs. With permitting and planning underway, February 2004 was chosen as the initial start date. In the meantime, Delaware Riverkeeper Network was busy scheduling the equipment operator, obtaining the needed materials, and coordinating with other project partners. Two weeks before the projected start of construction, a sewer-contracting firm began work on re-lining the regional sewer line running through the park. As a result, in-stream construction work was delayed until their completion and associated rain-delays.

It wasn't until the end of March that construction began on the Double Cross Vane. Using large 6.9 m³ (1 yd³) sandbags, flows were diverted around the active work area. The sediment-laden backwater was then pumped and filtered through a geotextile filterbag. Gravel and riprap were used to protect the exposed regional sewer line during construction. Following this armoring, this area was covered by gravel and silt excavated from the mid-channel bar. After rebuilding the eroded bank, the outer vane arm construction began by setting the downstream corner to bankfull elevation. From there, elevation readings were taken every 1.5 m (5 ft) to ensure the rocks were being set to their proper slope and angle. Construction on the inner arms began just before finishing the first outer arm, so the one side could be completed together. After completing the first side, the sandbags were repositioned to the opposite side of the creek to allow work on the other half. Construction involved use of an excavator and laser level surveying equipment, the latter due to the close tolerances required in the slope and angle calculations.

Environmentally-Sensitive Features

During construction, Delaware Riverkeeper Network staff monitored the effects of in-stream construction on the stream immediately downstream from the work area. Turbidity levels were analyzed to review the downstream impacts of construction. Throughout construction, turbidity levels remained below levels observed in natural high flows. Macroinvertebrate samples (taken both pre-and post-construction) showed no observable change in biodiversity or richness when compared.

In addition, a variety of wildlife was observed in and around the active work site during construction. Birds observed included Red-tailed Hawks, Northern Harriers, a pair of Wood Ducks, a group of Mallards, Goldfinches, and American Robins. White-tailed Deer tracks were observed on the newly created vane arms, indicating that they are using the vane as an easy access point in and out of the creek. Much to the anxiety of the equipment contractor, a resident water snake utilized the newly constructed vane arms as a sunning area. The most interesting of our wildlife observations was during construction of the second half of the vane. While building the inner portion of the vane, several large fish (probably white suckers) were observed swimming and resting in the newly opened channel in the Double Cross Vane.

Cross Vane construction took approximately four weeks including rain-related delays. After Cross Vane construction was complete, the fish habitat structures were installed. A series of stone deflectors were constructed along the left bank to create backwater pools and create cover for small minnow and fry. Stone deflectors were shaped like a 45/45/90 triangle (the 90° corner extending out into the channel approximately 4.5 ft (15 ft)). Three deflectors were installed approximately 30 m (100 ft) downstream of the Cross Vane, and four others upstream including one designed specifically to also protect a sewer line manhole. In addition, Boulder Clusters were installed upstream and downstream from the Cross Vane to provide backwater resting and feeding areas.

While construction of the Cross Vane was an interesting process, it wasn't nearly as interesting as the months following its completion. With five bankfull flow events occurring in June, July, August, and September (including flow events greatly exceeding the bankfull flow), the Darby Creek project was subjected to more high flows and flood events than most projects endure in 10 or more years. Both the riparian buffer and in-stream components of the project held well against the repeated stress. The only exception, observed after the August 1 flood event, dislocated boulders in a small section of the Cross Vane. The cause of the shifted boulders remains unclear, although we believe passing debris may have caused it. In addition, a gravel bar had also formed due to a Boulder Cluster being located to close to the Cross Vane structure. The gravel bar extended downstream far enough to interfere with the proper functioning of the right side of the Cross Vane. Both of these concerns were remedied during our maintenance workday at the end of August. Since then, the project has endured a major flood and possibly one additional bankfull flow event without problems.

Lessons Learned

1. Need for tighter controls on the size and shape of rock purchased and delivered to project. Calls had to be made with the quarry during mid-construction to ensure proper specifications were met.

2. Projects like this need to be carefully planned and even more carefully implemented with an appropriate amount of time set aside for unplanned events (bad weather delay, correction of mistakes etc.).

3. Project builders need to establish quality control procedures that result in all calculations being checked by a second party. An error in a set of calculations in this project resulted in re-construction of a section of the Double Cross Vane. The primary error was building with a set of calculations that had not been adequately verified.

4. Projects need to be completed with sufficient time left in the grant period in order to allow for “tests” under extreme conditions and/or repairs.

5. Staging the project to accommodate the needs of others (e.g. the sewer authority) yielded significant benefits in terms of cooperation, funding, etc.

6. Timing the project (starting on the heels of the sewer pipe re-lining) led to long-term misunderstandings and misconceptions by the public who assumed there was one large project instead of two.

7. The success of the project has created partner enthusiasm for additional work, both within and without the partnership itself. The success of this project has led to project partners pursuing additional projects of a similar nature in stream reaches upstream of the current project.

8. Restoration of Darby Creek including its riparian buffer, and the removal of homes inappropriately built on an urban floodplain represents a modern holistic approach to flooding and urban stormwater. Seeing it implemented successfully, not only demonstrates this for non-believers, but also affirms the faith of those who believed it previous to the project.

Photo Documentation:

All photos and Case Study information courtesy of Delaware Riverkeeper Network.