ICE-AFFECTED STREAMFLOW RECORDS USING TRACER-DILUTION DISCHARGE METHODS

摘要

Accurate ice-affected streamflow records are difficult to obtain for several reasons.rnProblems measuring stage, variable backwater conditions, access limitations inrnwintertime, and problems measuring flowing water under ice cover all contribute tornmake ice-affected streamflow records less accurate than open-channel streamflowrnrecords. The inaccuracy of ice-affected streamflow records is particularlyrntroublesome for small streams where Instream-Flow water rights exist. ThernColorado Water Conservation Board uses these water rights to protect in-streamrnaquatic communities. In January and February 2002, the U.S. Geological Survey, inrncooperation with the Colorado Water Conservation Board, conducted an experimentrnusing a sodium chloride tracer to determine streamflow under ice cover. The purposernof this study is to determine the usefulness and accuracy of ice-affected streamflowrnrecords using a sodium chloride tracer that was automatically injected into thernstream. The tracer was injected at two gaging stations once per day for up to 25rndays. Multiple-parameter water-quality sensors at the two gaging stations monitoredrnbackground and peak tracer concentrations and conductance. These data were usedrnto determine discharge at each site. A comparison of current-meter measurements torntracer-dilution discharge measurements shows an underestimation of discharge duernto inaccuracy of current-meter measurements with ice cover and inconsistent tracerpumprnrates caused by partial freezing of the tracer solution in the injection lines.