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• • Mike Savage February 9, 1981 Page 2 6) Questions 6, 7, 8 and 10 need to be addressed by TBM. Culvert designs cannot be evaluated as shown. TBM should remember that all culverts are affected by head loss at the entrance and outlet controlled culverts must take friction loss into consideration. TBM should contact us if clarification is necessary. 7) This adjustment is significant in long narrow watersheds; a common situation in diversion systems. 8) The curve numbers used by TBM are adequate. 9) Figures used in application of the Universal Soil Loss Equation (USLE) for LS are impossible to verify. I need to know how slope lengths were measured for determination of the LS factors given. From measurements made in the office LS figures appear quite low. 10) Spillway designs need to be upgraded. It is recommended that freeboard be allowed for full discharge capacities of at least one foot. This is simply sound engineering practice. This reviewer suggests use of the ogee spillway equation of Q = 4LH3/2 instead of the weir equation used by TBM. TBM should review their spillway design calculations presented in the October 7, 1980 Amendment. Spillways designed for ponds 22-P11, P12, P13, P14, P15 and P16 call for a spillway head of 20' (?). It appears that'h =2 feet is more accurate. Does TBM plan to use one spillway design for all ponds? TBM has, as yet, not addressed the problem of pond dewatering adequately. 11) Acceptable. 12) TBM must demonstrate to this office that the crossing at C-4 can safely pass the 10 year 24 hour event. If TBM can show that last year's heavy runoff represented the 10 year 24 hour discharge or more the Division will be satisfied. 13) TBM should redesign all culverts taking entrance and friction losses into account. This should be done after peak flow computations are adjusted for basin shape as mentioned in concern 1 of Bob Liddle's memo of December 8, 1980. 14) Acceptable.