3.2 Sedimentation

The sources of sediment contributing to the degradation of the stream are numerous and varied. Developing areas throughout the watershed, but primarily along the Alpine Avenue corridor, contribute sediments to the stream. Earthmoving and other construction activities are ongoing at many commercial and residential developments in the area. In addition, areas that are currently undeveloped, but which are zoned to allow for development, are expected to experience land use changes in the near future. Other sediment sources in the watershed include agriculture, stockpiles of soil, sand, concrete and other building materials, and roadways, bridges, parking lots and other transportation related sources.

Sedimentation of aquatic habitat is detrimental to many aquatic species. Soil particles fill in feeding and spawning areas, preventing the completion of the life cycle for many aquatic species. Coldwater fish and macroinvertebrate species habitat in York Creek has been severely impacted by sedimentation, and as a result there is little diversity of species, with almost no representation of species indicative of a healthy coldwater stream system. It is virtually impossible for those species to survive in a stream that has had sediment inputs in the amounts introduced to York Creek in recent years.

AWRI completed a streambank erosion inventory of York Creek and its tributaries as part of the watershed study. In order to assess the serious threat of bank erosion, AWRI used the streambank erosion inventory to estimate that to date, the total volume of soil introduced to York Creek through bank erosion is in excess of 124,000 cubic feet. AWRI contends that this is a conservative estimate as only those eroded areas of more than fifty square feet were included in the inventory. Site sketches were also completed at each location and are located at the Water Resources Institute. Additional study of streambank erosion, including the placement of benchmarks to aid in monitoring lateral recession, is recommended. This would aid in estimating annual losses, and in turn would be useful in determining the effectiveness of those BMPs selected for implementation.

There are incidents of stream bank erosion throughout virtually the entire watershed, but there are a few areas of particular concern, including:

• The entire Alpine-Walker Drain
• A wooded area between Cordes Avenue and Alpine Avenue
• Areas between Alpenhorn Drive in the York Creek Apartments and Four Mile Road
• Areas along Mill Creek Avenue

While the bank erosion inventory was ongoing, a cooperative effort between the City of Walker, Alpine Township, and the Kent County Drain Commission (KCDC) resulted in the installation of an instream grade stabilization structure in the Alpine-Walker Drain. The drop box structure is located in the drain near the turnaround of Kingsbury Street. The need for the structure became apparent after the discovery of two exposed sanitary sewer lines and a water main that transected the stream channel. Following the development of the Alpine Avenue corridor south of Four Mile Road, a substantial portion of which discharges into the Alpine-Walker Drain, the runoff from rain events eroded the stream bed to a depth estimated by the Kent County Drain Commission at between four and five feet. While the primary objective of the structure was to protect the exposed utilities, a secondary benefit was realized as the design structure created a small detention area upstream of the protected utility lines. One effect of this is the creation of a sediment depositional area which should slightly decrease suspended solids concentrations downstream of the structure.

Grade stabilization is a priority along the Alpine-Walker Drain where, according to KCDC, the slope is approximately two percent. (Connell, Dick, P.E.. 1994. Kent County Drain Commission. Personal communication.) Another grade stabilization structure, or a series of smaller structures, in the drain would benefit York Creek by reducing velocity, dissipating some of the stream's energy, and detaining water.

While there exists an elaborate administrative framework for the prevention of sediment leaving sites of land disturbing activities, current circumstances in the watershed prevent the efficient and effective completion of that framework. The Michigan Soil Erosion and Sedimentation Control Act, Public Act 347 of 1972, requires developing sites to follow prescribed guidelines related to control of sediment, but the local enforcement of those guidelines is inefficient. It is recommended that the local units of government investigate the possibility of becoming a local enforcing agent (LEA) and/or adopting local ordinances that would help to close the administrative loop around the issue of soil erosion and sedimentation control. Control of stormwater runoff would also be better administered through the use of local ordinances, and feasibility studies related to the adoption of a watershed-wide ordinance are strongly recommended.