7075 - Laserfiche WebLink

Home Browse Search

TABLE 33 Sediment Balance of Reduced Peak Flows Without Redistributing ---------- Percent ------------- Mean Annual --------------------- Annual Sediment Load ---------------- . Million Tons -------------- Years Balance Remaining ---- --- Flow, cfs Deerlodge Park ----- Mathers Hole --------------- Set to Zero --------------- -- - 90% ------------- 1976 ---------------- 2.327 2.472 32 80% 1810 2.059 2.141 25 70% 1643 1.800 1.827 10 65% 1560 1.674 1.676 2 64% ---------- 1543 ------------- 1.649 --------------------- 1.647 --------------- 0 ---------------- Again, as the daily flow pattern changes such that the peaks are reduced, the days in which the balance is set to zero declines. Only the high flow years of 1983-1985 are able to effectively reduce the balance as peaks are reduced further and further. Total transport at Mathers Hole is again greater than at Deerlodge Park, but as the flow distribution changes and is reduced, the balance is not set to zero as often and the loads at both locations approach being approximately equal. DISCUSSION OF RESULTS The total sediment balance for the Deerlodge Park to Mathers Hole reach shows the same general seasonal trend throughout the years. Sediment tends to accumulate during the baseflow months while the majority of annual load is transported during the peak flow periods and the balance is set to zero. If the timing or magnitude of peak discharges are significantly altered, sand deposited on banks and bars from late summer through winter may not be swept away seasonally (Elliott,1984). The sediment budget program tends to confirm this statement. ,-Again, this budget must be viewed in terms of trends. The accuracy of the results are only as accurate as the rating curves developed from measured flow and sediment values, the manner in which the distribution of flow values are changed, and the other assumptions presented earlier. The 'minimum monthly hydrographs' for the three scenarios are compared to the 'historic' hydrograph at Deerlodge Park in Figure 6 and listed in Table 34. Tables 35 through 38 show the mean monthly flows for the period of record for the four hydrographs.