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g. The total annual outflow was subtracted from the total annual inflow to get the annual loading. The fraction of bed load depends on the characteristics of the stream bed material, texture of suspended material, and the suspended sediment concentration. The bed load correction factors given in Table A-3 (Design of Small Dams, Bureau of the Reclamation, Department of the Interior 1987) were used to estimate the percent bed load in terms of suspended load. For concentrations less than 1,000 mg/1, the table gives a bed load correction factor of 25 to 150 percent of suspended load for sandy stream bed material. The trap efficiency of the lake was also calculated assuming different bed load concentrations (Appendix D). The trap efficiency of the lake is the percent of the total sediment inflow that is deposited in the lake The trap efficiencies calculated were compared with Brune's trap efficiency curve (Brune, "Trap • Efficiency of Reservoirs" June 1953) (Appendix D). Brune's curve gives trap efficiencies of normal ponded reservoirs as a function of detention time (lake volume divided by the annual inflow). Lake Orono has a volume of about 1,249 acre-ft. The annual inflow rate into the lake based on 1996 data is 222, 410 acre ft/yr (USGS data for Elk River near Big Lake). This gives a detention time of 0.0056 years. The corresponding trap efficiency per Brune's curve is in the range of 15-40 percent. This is comparable to the calculated values with bed loads of 50-100 percent of suspended load. Total sediment deposition was calculated to be between 880 and 2,500 tons per year assuming bedload contribution in the above range. Based on bedload at 75 percent of the total suspended load, net deposition is approximately 1,700 tons, or approximately 1,700 cubic yards, per year in Lake Orono. Spread evenly over the lake's 254 acres, it represents a deposition rate of 0.004 feet/year. This is about one fourth of the deposition rate previously calculated by comparing the 1970 and 1996 DNR lake surveys. The sediment deposition is, however, likely to occur primarily in the upper portions of the lake and is probably not evenly distributed over the whole lake. Sedimentation in Lake Orono consists of primarily the coarser • N\0596\0I\ELKRJ VERRPT-NCW 1 2