Hydrological tracer testing is an effective way for assessing the significance and extent of leakage through the bed of an influent (losing and sinking) stream. In karstic terranes, leakage from losing and sinking streams typically resurge at downstream springs, but flow may be intercepted by production wells. Although sinking streams that disappear into swallow holes and caves are relatively easy to trace, developing a tracer test design for a losing stream that allows slow percolation through its bed is complicated by the lack of basic knowledge regarding leakage rate, leakage locations along its length, and temporal variability. To overcome these complications, modification to the Efficient Hydrologic Tracer-test Design (EHTD) program were undertaken. Simultaneous use of both pumping wells and springs as sampling stations constituted initial modifications to EHTD. Additional modifications were then taken to address the problem of losing streams by using the total volume of flow leaking through the bed of a losing stream as determined by taking the difference between upgradient and downgradient discharge measurements or as estimated from the effective porosity of the stream bed. Leakage rate may be set if measured or may be taken as a function of the estimated mean travel time for the losing stream. These modifications are also effective for dry stream channel in which an artificial flow is necessarily added to facilitate a tracer test.



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