StreamflowandRunoffThecharacteramountandtimingo.pptVIP

* * Streamflow and Runoff The character, amount, and timing of discharge from a basin tells a lot about flow paths within the basin Therefore, important to hydrogeologist to identify how to create stream hydrographs from discharge measurements Measurement of discharge: Method used depends on type of study, size of river and flow, data requirements, etc. For small scale field studies discharge is measured over a cross-section at the point of interest using: a) float method - time surface float from point a to point b - average velocity is 0.85*surface velocity - mean velocity*x-sectional area = discharge - measurement distance should be ~10x stream width - very rough estimate b) stream gage - average velocity in a stream occurs at 0.368*depth above the bottom - therefore standard to measure along a cross-section at 0.4 depth off bottom - for more accurate estimates, averaging and depth measurements can be made.. c) dye dilution - good method for turbulent streams - need to use tracer that is a) easily soluble, b) have no or very low natural concentrations in stream, c) be conservative, d) easily detectable at low concentrations, e) ecofriendly, f) affordable - sodium chloride (NaCl) often used, and concentration/conductivity relation established - by introducing tracer upstream and measuring rate of concentration change downstream we can calculate discharge for the stream reach for a gulp injection where CT is the initial tracer concentration being introduced Cb is the background concentration in the stream and the integral in the denominator is evaluated graphically from a C vs. t plot.. d) direct measurement - can be used in small streams where it is possible to focus all flow into a collector More “Permanent” installations can be made using: a) - Dam (plate) with a v-notch (typically) that allows for controlled discharge through the notch. - discharge can be related to the height of the back-water - problems with sedimentation Rect