19-09-2017, 03:09 PM
In 1976 Dennett Tennant introduced a method for determining reserve water flow requirements for fish, known as the "Montana method", or more commonly the Tennant method. The method uses a percentage of the average annual flow (AAF) to determine the quality of fish habitat. Of the 58 cross-sections of 11 brooks in Montana, Nebraska, and Wyoming, Tennant concluded that 10% of AAF is the minimum for short-term fish survival, 30% of AAF is considered capable of sustaining equitable survival conditions, and 60% of AAF is excellent to exceptional habitat. These quantities are used internationally, regardless of their physical and hydrological configuration, due to the simplicity of using only the average annual hydrograph.
The Tennant method was tested to see if the percentage of AAF can actually be used as a substitute for other hydraulic measures, such as width, depth, and velocity. These physical parameters have been used in other studies to quantify the feed flow used for fish. The other two methods that were used in the comparisons were the wet perimeter method and the physical habitat simulation system (PHABSIM). A set of regional characteristics was used to look for patterns specific to each region. These characteristics include: type of stream, state, ecoregion and hydroclimatic regime. A total of 151 cross-sections were analyzed in seventy river segments throughout the western United States (California, Colorado, Idaho, Montana, Oregon, Utah and Washington). The streams were classified as pool riffle, flat bed, step-pool, and dune-ripple. This study will provide resource managers with additional information on the applicability of the Tennant method to determine current water flow needs for the physical, biological and social environment.
The data collected from lower gradient currents in Nebraska followed the patterns established by Tennant much more closely, and therefore the Tennant method is more applicable in similar low-gradient currents (slope less than 1%). In higher gradient streams, the use of the Tennant method should be with caution and be restricted to the planning stages of water flow recommendations. Validation and adaptation of additional methods are recommended when using the Tennant method for higher gradient current types. The Tennant method should be used in wastewater flow protection scenarios and not in restoration scenarios due to the assumption that the current average annual hydrograph represents the optimum fish habitat.
The Tennant method was tested to see if the percentage of AAF can actually be used as a substitute for other hydraulic measures, such as width, depth, and velocity. These physical parameters have been used in other studies to quantify the feed flow used for fish. The other two methods that were used in the comparisons were the wet perimeter method and the physical habitat simulation system (PHABSIM). A set of regional characteristics was used to look for patterns specific to each region. These characteristics include: type of stream, state, ecoregion and hydroclimatic regime. A total of 151 cross-sections were analyzed in seventy river segments throughout the western United States (California, Colorado, Idaho, Montana, Oregon, Utah and Washington). The streams were classified as pool riffle, flat bed, step-pool, and dune-ripple. This study will provide resource managers with additional information on the applicability of the Tennant method to determine current water flow needs for the physical, biological and social environment.
The data collected from lower gradient currents in Nebraska followed the patterns established by Tennant much more closely, and therefore the Tennant method is more applicable in similar low-gradient currents (slope less than 1%). In higher gradient streams, the use of the Tennant method should be with caution and be restricted to the planning stages of water flow recommendations. Validation and adaptation of additional methods are recommended when using the Tennant method for higher gradient current types. The Tennant method should be used in wastewater flow protection scenarios and not in restoration scenarios due to the assumption that the current average annual hydrograph represents the optimum fish habitat.