WSP09785 - Laserfiche WebLink

Home Browse Search

?- "..,..... "\ UOr.;0 where: Streamflow loss = average. loss (+) or gain (-) during the estimated period in a river reach, in cubic feet per second; RI = mainstem streamflow entering a river reach at the upstream site, in cubic feet per second; TI = tributary streamflow entering a river reach at all gaged tributaries, in cubic feet per second; DO = diversion withdrawn out of a river reach by all irrigation canals, in cubic feet per second; RO = mains tern streamflow leaving a river reach at the downstream site, in cubic feet per second; and dS = change in storage within the river reach during the estimated period, in cubic feet per second. Streamflow losses (positive values) can result from evaporation from the river and saturated soil surfaces, from transpiration by phreatophytes in adjacent flood-plain areas, and by an outflow to ground water. Streamflow gains (negative values) can result from an inflow of ground water and from ungaged streamflows contributed to the river. Daily records of diversion outflow (DO), mains tern reach inflow (RI), and mains tern reach outflow (RO) were used for 1957-67 and 1984-92. Daily tributary inflow (TI) records were used for two tributaries [sites T1 and T2 (fig. 1)] in reach I (1957-67) and for five tributaries [sites T3 to T7 (fig. I)] in reach 2 (1984-92). No records of tributary inflow were available for reach 3. Change in storage (dS) within a river reach during the specified period was assumed to be negligible. To minimize the error introduced by this assumption, the accounting period was adjusted (upstream traveltime adjustment) so that the same streamflow peaks were included in the average streamflow into (RI) and out of (RO) the reach. Streamflow loss was calculated for daily periods and for streamflow-event periods. For daily streamflow- loss estimates, the flow hydrograph from the upstream site was visually compared to the flow hydrograph from the downstream site to select an appropriate traveltime by which to adjust each period for the upstream site. The leading edge, streamflow peak, and the trailing edge for each pair of distinguishable streamflow events were compared (fig. SA). A single constant traveltime adjustment (fig. 8B) was used to estimate traveltime-adjusted streamflow into each river reach for 1957-67 (reach I) and 1984-92 (reach 2 and reach 3). Streamflow loss also was calculated for selected streamflow-event periods. Streamflow events having similar characteristics (leading edge, streamflow peak, and trailing edge) at upstream and downstream sites (first and second periods in fig. 9) were selected. Streamflow events lacking these similarities (third period in fig. 9) were not. Streamflow loss or gain was computed for each period using the cumulated mainstem inflow (RI) at the upstream site (area under the curve from VI to V2 in fig. 9), the cumulated mainstem outflow (RO) at the downstream site (area under the curve from 0 I to 02 in fig. 9), the total inflow at gaged tributaries (TI), and the total irrigation diversion outflow (DO). Thus, when total inflow exceeded total outflow, water was lost in the river reach and, when total outflow exceeded total inflow, water was gained in the river reach. Reach 1 Tracking of specific streamflow peaks was not possible through reach I; therefore, available streamflow data in reach I were inadequate for determining reasonable estimates of traveltime. Visual inspection of many daily streamflow hydrographs for sites QI, QIA, QIB, QIC, and Q2 also indicated that large and almost continuous inflows of ungaged water (either field tailwater, canal wastewater, return flows, or ungaged tributary inflows) entered into reach I on a regular basis throughout the irrigation season. Lacking reasonable estimates of traveltime and the ungaged side-channel inflows into reach I prevented accurate determination of stream- flow gains and losses. Reach 2 Analyses of daily mean streamflow gains and losses for reach 2 were made for more than 2,900 days between 1984 and 1992. A constant I-day advance (traveltime adjustment) of the upstream flow, which STREAMFLOW GAINS AND LOSSES 17