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oocurrence,;. The majority of exi,;tiny cro~>;iny>; have be",n left in place, although their capacity may be as small as the 5 year runoff. In specific areas where economic analysis indicated that the benefits derived from a new street crossing would be greater than the cost of that crossing, new facilities have be~n recommcnded. area. The approach taken in the In<l,;ter pldrl i8 tu in>ltdll illl additional conduit from Jewell to Wadsworth consistent with existing development and uti1ity constraints and then determine the frequency storm which can be passed by the structures. SANDERSON GULCH THROUGH LAKEWOOD From the Jewell crossing to the Jewcll Park area, the standard design criteria of 10 ycar frequency conduits together with a Channel capable of transmitting a 100 year storm has been possi- ble. Again in this area, Lakewood is concerned that Jewell Avenue remain open during a lOO year storm event. Particular care must then be taken with street crossings to assure that the 100 year storm does not infringe upon Jewell Avenue excessively. The first area encountered in Lakewood on Sanderson Gulch is the Bit- O-Sea Development which is clustered around 2 recreational reservoirs. Based upon the legal aspects of these reservoirs, and the desire of the residents that they remain in their existing condition, the design criteria for this area is to assure the safety of the reservoirs with a minimum of disturbance to the area. Criteria for the Jewell POnd involved improving it to function as an effective detention reservoir while fitting with the park development. Directly above Bit- O-Sea Reservoir area is the Clair field Reservoir. This reservoir is still in an undeveloped area and repre>;ents an excellent opportunity to develop a necessary flood detention facility. The criteria here is to maintain the 100 year flood pool with improvemcnts as near as possible to the historic 100 year flood pool area. The reservoir must also be improved to a state that is acceptable to the State Engineer in a developed area, while having a ~aximum effect as a flood control reservoir. Within the Jewell Park area is the ~rossing of Agricultural Ditch across Sanderson Gulch. In compliance with the recommenda- tions of the legal counsel, together with good engineering prac- tice, a suggested method of separating flows in this area was designed. The criteria for this grade separation is that run- off from storms up to the 100 year frequency in the main gulch Should not enter the irrigation ditch. The next area with speoidl design considerations on Sanderson Gulch is the Green Gables Country ClUb Entrance Road Area. The area above this entrance road is subject to inundation on a very frequent basis due to the very small culverts under the road. It wa~ originally hoped that this road could be left in its existina condition to act as u flood detention reservoir with, the only improvements being placing of slope protection On the downstream side of the road. Additional surveying indicated major errors in the available mapping such that the frequency of the inundation for the road became too often for acceptable standards. The next area where specific design criteria was employed occurred at Smith Reservoir where the criteria was to develop a method to maintain spillway discharges from Smith Reservoir in the Sanderson Gulch Basin. NORTH SANDERSON GULCH The final cesign criteria adopted for the Green Gables site involved the design of larger conduits beneath the road fill and raising the road fill to a point where the reservoir routing effect made the conduits capahlp of passing a 100 year storm beneath the road. This approach will significantly reduce the frequency of inundation to the golf course area and overtopping of the road. The specific design criteria on North Sanderson Gulch from Pierce Stroot to Florida Avenue was essentially the Sdffie. A channel was developed with a maximum capacity reasonable within the available right-of-way and remaining flows were allowed to continue along the street system. This approach generally moans that crossings are designed for a lO ycar frequcncy with the channel capacity bcing somewhere between a lO year and lOO year capacity. One exception to this is the Wadsworth crossing which i~ capable of conveying the 100 year storm rUnoff across Wadsworth Blvd. as requested hy the City of Lakewood. The conduit in Florida Blvd. is intended to carry local drainaqe from the surrounding area and base releases from the Grecn Gable's Park detention pond. Additional flows arc to be carried On the street surface with reasonable limits of inundation. Oesign oriteria for the area from Wadsworth Blvd. to Jewell Ave~ue was influenced by the city of Lakewood's request to increase thc capacities beneath Jewell and wadsworth to values approaching the Ino year occurrence. Meeting the requirement of passing a 100 year storm beneath the mentioned streets would have been particularly expensive in this location, since a Conduit would have been necessary across the Jewell-Wadsworth Shopping Center The Grcen Gables Park improvements criteria as agreed to with the Park and Recreation District involves leaVing the pond in as -82- -IU-