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Stream Flow: The Importance of Reducing Excessive River Flows


The Rouge Project recognizes that stream flow is a critical element in the health of the Rouge River. Research has shown that flow is an important factor in meeting water quality standards. A stable stream flow is usually an indicator of a healthy river. Erratic stream flow as measured by velocity and volume of water that travels in a stream can lead to a multitude of problems. At one end of the spectrum of erratic stream flow is when there is too much water in the river which results in flooding. Flooding causes obvious problems such as the physical destruction of property in the flood plain, severe water quality problem that result from the flooding of sewers and the pollutants carried off from the flooded land, severe erosion of the stream banks, etc. High river flows that fall short of floods also cause major problems associated with scouring the stream bed which destroys streambed habitat and stream bank erosion. Stream bank erosion results in two major problems.

The first is the physical destruction of the banks which destroys property, causes log jams from the trees that fall into the river, and is an aesthetic problem. The second problem is the resulting sediment that enters the river. This sediment alters the fragile aquatic habitat by "smothering" the bottom of the stream by filling in the pockets between the rocks and gravel of the stream bed that aquatic species depend upon. The sediment also carries pollutants such as phosphorus into the river which can cause insult to the aquatic species by various impacts such as decreasing oxygen levels. At the other end of the spectrum of erratic flow is when the flow in the stream is reduced to extremely low or zero flows, which results in the degradation and/or destruction/loss of habitat.

USGS and the Rouge Project monitor flow at various stations across the Rouge River watershed. An analysis of USGS data confirmed that there is a high degree of fluctuation in the flows in the Rouge River. This fluctuation in flow is a direct result of increased urbanization development and loss of permeable soils and wetland storage in the watershed. The gauging station data on the Rouge River has shown a four-fold increase in the average number of annual flood events over the last twenty-five years, based on a five-year running average.

Based on the recognition of flow as a pollutant source and due to the fact that many communities within the Rouge River watershed have been experiencing an increasing amount of stream bank erosion and flooding along the river, the Rouge Project encouraged local communities to address this issue as part of the subwatershed management plans and storm water pollution prevention initiatives, as part of the Michigan General Storm Water Permit.

Several subwatersheds in the Rouge ranked flow as a second highest priority in their subwatershed management plans, only behind the protection of public health. The more urban subwatersheds noted that the management of storm water flows in existing developed areas is one of the greatest challenges in restoring the river. Even with total control of pollution sources, the biological and physical attributes of the river cannot be fully restored without significant reduction in the impacts caused by the increased frequency, duration, and size of flows following storm events.

The Rouge subwatersheds are also addressing the issue of flow through their Storm Water Pollution Prevention Initiative (SWPPI). The SWPPI includes evaluation and implementation of pollution prevention best management practices to minimize the impacts of new development and redevelopment.

Both the subwatershed plans and the SWPPI call for implementation of best management practices (BMPs). Below is a list of some of the BMPs being addressed in the Rouge planning process, including several that can be implemented to address river flow issues. The alternatives listed below may apply to one community but not to another, so it is important to note that each of the alternatives is a unique solution to a specific pollution source or problem.

Storm Water and Water Resource Protection Ordinances
In undeveloped areas, or in an area where redevelopment may occur, it is important to have regulations in place that can guide land development with regard to protecting water quality, quantity, and the biological integrity of the receiving surface water. This regulation can use existing data to determine the development impact that can be tolerated by the surface waters before the system becomes degraded. Future development or redevelopment can be guided to control runoff so that local streams and water resources are not negatively impacted.

Land Use Planning and Management
This involves a comprehensive planning process to control or prevent runoff from certain developed land uses where receiving waters are sensitive to development. The overall planning process involves the following steps: 1) determine water quality and quantity goals with respect to human health, aquatic life, and recreation; 2) identify the planning area and gather hydrological, chemical, and biological data; 3) determine and prioritize water quality needs as they relate to land use and proposed development; 4) develop recommendations for low impact development to address the problems and needs that have been previously determined; 5) implement recommendations.

Reduce Directly Connected Impervious Surfaces
Development plans can be created to combine a hydrologically functional site design with pollution prevention measures to compensate for land development impacts on hydrology and water quality. The result will be a reduction in storm water peak discharge, a reduction in runoff volume and the removal of storm water pollutants. This can apply to new residential, commercial, and industrial developments. In urban communities, especially older areas, there may be opportunities to disconnect impervious areas through downspout disconnection and the disconnection of sump pumps to driveways and sewer systems.

Slow Storm Water Runoff (Storage Facilities) in Urban Areas
In older urban areas where storm water detention systems do not exist, storm water storage facilities may be considered. These facilities are underground control devices that are designed to retard flow sufficiently to reduce sewer overflows, prevent downstream flooding and/or reduce velocities. These facilities consist of storage tanks connected to the existing drainage system, street storage, and parking lot storage.

Install/Maintain Storm Water Retention Basins and other Infiltration Devices
Storm water infiltration basins are any storm water device or system, that causes the majority of runoff from small storms to infiltrate into the ground rather than being discharged to a stream. Most infiltration devices also remove waterborne pollutants by filtering the water through the soil. Storm water infiltration can provide a means of maintaining the hydrologic balance by reducing impervious areas. Infiltration devices could include the following: basins, trenches, permeable pavement, and other systems that collect runoff and discharge it into the ground.

Construct and Maintain Wet Detention Ponds and Constructed Wetlands
Wet detention ponds, or constructed wetlands, are small man-made ponds or shallower areas with wetland vegetation around the banks designed to capture and remove particulate and dissolved matter. Wet ponds and wetlands are ideal for large, regional tributary areas where there is a need to achieve high levels of particulate and dissolved nutrient removal. The pond or wetland should be sized to treat runoff, accumulate sediment, and route floods. The pond should be configured for aesthetics, safety, and maintenance. Landscaping design requirements should include a natural vegetated buffer around the pond/wetland to reduce pollutants entering the area as well as decrease goose habitat and increase aesthetics. Proper monitoring and maintenance is necessary for five to ten years after construction.

Construct and Maintain Dry Retention/Detention Ponds
A detention basin is usually dry between storms. It is designed to capture runoff and release it slowly to allow most of the polluted sediments to settle. Dry retention/detention basins are used for tributary watersheds 10 acres and larger in size to attenuate peak flow and remove particulate matter. The basin should be designed to treat runoff, accumulate sediments and route floods. It should be designed for aesthetics, safety and maintenance.

Learn more about BMPs, their applicability, pollutant removal ability, and costs in a detailed BMP report.

Interactive Stream Flow Data Map

Stream Flow: The Importance of Reducing Excessive River Flows

Last Updated: 8/6/2003

Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -07 and C-264000-01.