| Popis: |
The Arkansas Department of Environmental Quality (ADEQ), through an EPA Section 319 NPS grant, utilized a bank erosion hazard index (BEHI) and data collected from surveys of streambank profile measurements to develop a graphical model to estimate streambank erosion rates and to estimate the annual sediment load due to accelerated streambank erosion in the West Fork White River (WFWR) watershed. The WFWR watershed, located in Northwest Arkansas, has a watershed area of 31,700 Ha (79,400 ac) and is a tributary to the White River which eventually drains to the primary drinking water source for the region, Beaver Lake. Sediment is a contaminant of concern because the WFWR has been designated as impaired due to “excessive turbidity and siltation” (ADPC&E, 1998). As part of a comprehensive project to assess the various sources of sediment in the WFWR watershed, ADEQ utilized methods, developed by Rosgen (2001), to estimate sediment (bedload and suspended) contributions from accelerated streambank erosion. A streambank erosion inventory was conducted in 2002 to determine the bank erosion potential of streambanks along 64 river kilometers (40 river miles) of the main stem and tributaries of the WFWR watershed. Using ranking criteria consisting of bank angle, root depth, bank material, and other variables, streambanks were evaluated and scores were assigned based on erosion potential. Toe pins were installed at permanent survey sites and lateral erosion was measured over a one-year period. A graphical model to predict streambank erosion rates based on relationships between BEHI, near-bank sheer stress, and observed annual erosion was developed. For the WFWR watershed, it was estimated that on an annual basis, a total of 21,455 metric tons of sediment enter the river network from streambanks where accelerated streambank erosion was observed. The mass of bedload and suspended load was 7,493 metric ton/yr and 13,962 metric ton/yr, respectively. |
