Case Study
Conowingo Creek Case Study
Spring 2023
In 2018, a landowner came to the Lancaster County Conservation District (LCCD) and Donegal Trout Unlimited (DTU) with significant sedimentation and erosion issues on their property along the main stem of the Conowingo Creek. Some of the issues the stream was facing included ten-foot vertical stream banks, lack of tree cover and habitat, and unrestricted livestock access. Without a tree canopy, the stream has higher temperatures, low-quality habitat, fewer food sources, and a reduced aquatic community. In some cases where the damage is less severe, simply planting trees, excluding livestock, and allowing the stream to repair itself is the solution. But, what can we do with a situation as developed as this? This situation calls for a more intense reaction, something that will help reset the years of unmitigated damage to the stream while setting it up for success in the future. The prescription here is stream restoration, exclusionary fencing, and a riparian buffer, funded by an EPA 319 grant and Keystone Protein settlement funds through the Lower Susquehanna Riverkeeper Association. The project was designed and permitted by LCCD, and constructed in partnership with the U.S Fish and Wildlife Service, Habitat for Forever, and Unique Excavating, with construction oversight from LCCD.
The landowner’s stream before construction. Notice the eroded stream banks and lack of trees.
Bank grading helped smooth the steep eroded stream bank. Planting trees will help stablize the bank for years to come.
Project design begins at the first visit to the property, where we look for signs of erosion and attempt to ‘read the stream’ to determine what may be the cause of degradation. Sometimes issues are easy to assess, while others may require deeper analysis and searching upstream or downstream. Common issues include straightened streams, dams, old mills, misplaced rock and concrete, lack of woody vegetation, unrestricted livestock access, new construction, and non-porous surfaces like parking lots and warehouses. Due to the complexity of streams, the planning and design stages regularly take longer than the construction or implementation stages. Once the design is finalized, permits take between two to six months from submission to approval. As soon as the approval letter is received, we can start construction.
When it comes to construction, stream projects are unique because of how much work is actually done within the stream channel itself. Streams do not stop running just because we’d like to work on them, so everything must be thoughtfully done to reduce the impact to our downstream neighbors while construction is in progress. In addition to careful planning, a high level of precision is absolutely necessary due to water’s self-leveling characteristics. If a structure is placed improperly, the stream will make it clear by potentially undercutting the structure itself or diverting in a completely different direction than anticipated. This project has a diverse set of structures that all play an independent role to improve stream health overall. Some structures, such as mudsills and boulder clusters, act as habitat for macroinvertebrates (aquatic bugs) and fish. Other structures, like vanes, are used to direct the flow of water in a way that will benefit the stream. Riffles are placed regularly to allow the water to churn and dissolve oxygen from the air into the stream, which has a direct impact on the organisms living within it. Equally as important as the in-stream structures is the bank grading, which removes those 5 to 10-foot vertical banks and instead gives the stream banks a gentle 1:3 foot ratio, meaning for every 3 feet away from the stream’s edge, the banks rise 1 foot. This is essential for reconnecting the stream to its floodplain. If a stream is not connected to the flood plain, all of the energy of the water during a flood event is directed into the stream banks, further causing erosion. Once a stream is reconnected to the flood plain, it is able to disperse that immense energy out to flatter ground, and the water will percolate into the ground naturally. Other structures included in this project are rock toe and zig-zag wall for armoring the banks where the potential for erosion is highest.
Once construction is complete, the stream is in a much better condition than it was before, but it is more vulnerable than ever due to the construction process. Soil that was previously heavily compacted has now been disturbed and re-shaped and needs to be held in place while it settles. This is accomplished in two steps; first, a seed mix is spread onto the bare soil and covered with straw mulch. Grasses will grow very quickly, and the roots will act as the first line of defense to hold soil in place from rain events. In order to truly freeze that soil in place for decades, trees need to be planted in the area next to the stream, which is known as a riparian buffer. In general, about 200 trees and shrubs will be planted for each acre. Fast-growing species like sycamore and tulip poplar are excellent at getting deep, strong roots in place to truly hold the stream bank in place while slower-growing but long-lived species like oaks will ensure the stream is protected for hundreds of years to come. Wildlife species like nannyberry and elderberry will allow insects, and therefore birds, to flourish within the riparian buffer. The added habitat will allow small mammals like mice and squirrels to thrive, and therefore predator species like foxes are able to succeed as well. Additionally, the trees will act as a corridor that animals can use to safely travel from forest to forest.
After tree buffer planting!
Final Result
The Conowingo Creek Restoration Project is a testament to the many partners working hard in this watershed to improve the streams and the community living along them. In total, 3,180 linear feet of streambank were restored and a 4.5-acre riparian buffer with fencing was completed. While it will take time for the trees to grow and the stream to begin healing itself, we can be proud of a project that created in-stream habitat and reduced nutrients and sediment to the Chesapeake Bay.
— Watershed Team at the Lancaster County Conservation District
Before Construction
During Construction
After Construction
