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-5- - in determining the entrance head-loss (Ke) for Pond I and the Pond 4 Afain Spillway design, the designer erroneously used a bend-loss coefficient nomograph. The Ke given in the design is 0.25, which is appropriate for a round 90o bend bend-loss coefficient (Kb), but inappropriate For an inlet Loss coefficient. Using Table 4-9, page ISG, of the "Handbook" shows that projecting inlet culverts have an entrance loss coefficient of 0. 9. - in determining bend-loss coefficients and friction losses, the designer has used two homographs eahi~ch give friction losses. The friction loss is correctly determined, but the bend-loss coefficient is incorrect for each of the spillway designs. (Please see the last paragraph of page 189 in the handbook.) - in determining the total head-loss (H L), the designer has ignored the elevation head necessary to develop the velocity head. In order to show what inadequacies these errors cause in the design, a sample design for the headwater of Pond 1 is given below: Ke = entrance loss coefficient = 0.9 Kb = . bend-loss coefficient = 0.40 (see 3 - Bends, page Z89 of "Nar7dbook of Steel Drainage and Highway Construction Products") !ff = friction head loss = 0.04 ft/ft 2 HL = head loss = (1 + + Hf(L) xe+xb) 2 J 44 cfs Q y _ _ = 8.96 fps A 9.92 f2 8.962 HL = ) + (I + 0.9 + .40) ( 0.04 (40) 64.4 HL =• 4.47 The submission by Dorchester Coal Company shows a head loss of 1.96' and an available head of 4.0 ft. A HL of 4.47' indicates that the pond would overflow prior to 44~cfs of flow passing through the emergency spillway. From the design information provided, it appears that highly erosive velocities occur at the outfall of all culvert spillways. A vertical component of velocity in excess of 17 fps could be expected from a culvert with a freefall of five feet. On page 5, 2.05.3(4), Volume 2-A, a statement that "All spillway culverts at the Dorchester kl mine have a minimum free-fall of 5 feet ..." occurs. Such an outfall velocity would require substantial channel protection to prevent serious erosional problems. Also of concern is the lack of information on available freeboard in spillway designs. A discussion of the available freeboard should be included in the design, in accordance with (4.05.6(8)(c)). If less than one foot of freeboard is provided, a discussion of embankment protection should be included.