Stream Consultation
Brightwater has extensive experience in the assessment and restoration of rivers and stream systems. This experience has included stream classification, quantitative evaluation and diagnosis of channel stability problems, restoration design, construction supervision, and geomorphological and biological monitoring of restored streams. In addition, the company has a unique understanding of the hydrological and ecological relationships between fluvial systems and adjacent riparian and wetland habitats.
Stream channels develop their shape, size, slope and other morphological features as a result of the interaction of flowing water on the materials in the stream's valley. A stream or river is the manifestation of a process of energy transformation in which potential energy of elevation is transformed into the kinetic energy of flowing water. In this process of energy use and transformation there are eight variables. They are discharge, width, depth, velocity, slope, roughness, particle size and sediment quantity. The independent variables are discharge and sediment load.
Discharge can be modified by changes in land use that affect the fate of precipitation by imposing alterations to infiltration, evapotranspiration, storage or runoff. Sediment quantity is affected by the type and distribution of rocks, vegetation, and the effects of weathering and transport. Land use changes such as the conversion of forest to residential or commercial development can have a dramatic effect on the hydrologic cycle. This occurs principally because these land use changes permit more runoff to occur and allow that runoff to concentrate faster. When this happens, stream channels respond by enlarging to accommodate the greater volume of runoff generated by peak annual storms.
When stormwater management is employed to maintain the pre-development peak discharge rates for certain storm events, it is often the increased duration of bankfull flows that causes channel adjustment.
In either case, the process of channel enlargement can proceed like a chain reaction once started, because as channels enlarge, they generate excess sediment from bed and bank erosion. The excess sediment often exceeds the transport capacity of the stream resulting in depositional features downstream of the initial sediment sources. These deposits reduce the capacity of the channel to carry the frequent high flows. The stream responds by eroding its banks to regain its capacity. This process generates even more sediment, which causes more bank erosion downstream. The process thus accelerates in a downstream direction, and it is not unusual for stream channels to enlarge more than twenty-fold over a period of several years.
During this period of channel enlargement accelerated by excess sediment, aquatic habitats are severely degraded. Fine sediment fills all the spaces in the gravel and rocks that cover the stream bed. Aquatic insects that inhabit the bottom of the stream are unable to survive. These insects perform many important functions in a healthy stream. They process the leaf fall and other organic material that enters the stream, and they become food for larger organisms such as fish. When these aquatic insects are gone, most fish disappear and the inputs of leaves and twigs flush downstream where they decay anaerobically, depleting downstream receiving waters of oxygen.
Recently, techniques have been developed for restoring degraded streams. A stream classification system developed by David Rosgen while he worked with the U.S. Forest Service is being used to determine stable forms of stream channels. The technique enables one to restore stable morphologic parameters such as width/depth ratios, meander radii, and sinuosity. Once the correct geometry has been determined, non-structural techniques such as bank stabilization with root fans of trees, and re-vegetation of banks can be used to restore a natural looking stream channel which provides good habitat for aquatic life.
For over ten years, Brightwater, Inc. has specialized in
practical applications of fluvial geomorphology and the use of bioengineering and native
material revetment techniques to restore disturbed streams to stable, natural habitats.
This experience has included:
- Evaluations of more than 125 streams using the Rosgen stream classification system;
- Over two dozen successful stream restoration designs with construction supervision;
- Design and implementation of geomorphological and biological performance monitoring programs for restored streams which has led to continuing improvements in design standards and construction techniques;
- Conducting numerous short courses to train individuals from government regulatory agencies, consulting engineering firms, and state federal and local government personnel responsible for capital projects for restoration or mitigation.
Related services include:
- Stream Quality Impact Assessment - Provide assessment of the stream's flow regime, energy source, habitat structure, and water quality.
- Stream Quality Monitoring - Design and conduct stream sampling programs to assess current water quality, stream channel stability, aquatic life and temperature regime to document effects of changes in land use or land cover. For stream restoration or mitigation requirements, post-construction monitoring capabilities are also available.
- Stream Restoration - Plan and implement strategies to restore destabilized stream systems. By assessing natural stream conditions, i.e geology, hydrology, hydraulics, and geometric factors, the pre-disturbance stream pattern is determined. By defining slope, bankfull width and depth, and sediment size distribution, the stable meander pattern and sinuosity can be restored reversing adverse impacts on stream structure and function.
- Stream Bank Stabilization - Design and implement stream buffer strategies to reduce or eliminate stream bank erosion. This includes the use of non-structural or structural technologies dependant upon existing conditions.
- Habitat Improvement - Assess habitat deficiencies and provide reclamation treatments to enhance aquatic habitat structure and production.