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II -10 SPECIAL CONSIDERATIONS/HAZARDS Lena Gulch has a multitide of problems that are quite serious. Six areas of hazard potential to life and property, however, can be singled out. These hazards are Apex Gulch, Jackson Gulch, floodplain trailer courts, Maple Grove Reservoir, Reach 9, and Reach 11. Apex Gulch. Apex Gulch would be susceptible ~o damage and would cause increased damage downstream from heavy flash {:loodill~l and erosion if de-- veloped because of the relatively steep side slopes, steep channel slopes and the non-cohesive nature of the soil material. Apex Gulch Forest Land, as well as the south facing slopes, has an average slope of 31 percent. This exceeds a reasonable 20 to 25 percent siope limit for devejopwent. Development of Apex Gulch would nOi: lend itself to detention storage with- out excessive efforts and costs. Thahleg storage would create adverse environmental impacts. Planned Unit Development (PUD) in this portion of Basin 1, leaving the slopes free OC development, could achieve hydrolog- ically satisfactory results if done properly. I:~ is suggested that the U.S. Geological Survey hazard and development criteria be used here. A large percentage of this Gulch has been purchased for open space. The re- mainder should be carefully observed. Jackson Gulch. This gulch, to the south of Apex Gulch, is already being developed and altered by Man. Steps should be taken J?.y the land owners and developers to control erosion I-ate'.., and jmplernel;t:~edim::.ntatron me~s- ures so that Lena Gulch and developments below are not subject to sedi- mentation and debris hazards. A small pond, listed as Magic Mountain Dam No.1 by the State Engineer's Office, is located on the mainstream of Jackson Gulch. (See Sheet No. 21). The dam itself is approximately 30 feet high with a top width of 15 feet and a crest length of 540 feet. The spillway is essentially a broad crestec wier 28 feet wide with a head clearance of 4 feet before the low chord of the railroad bridge passing over 't. The approximate safe discharge capa- city of the spi Ilway is estimated 1:0 be 700 c1's. This would be capable of handlingmore ~han 100-year peak flow feOIT! this pal"tion of the basin. The further development of this basin should take this into consideration by planning long duration detention filcilities so that the spillway capacity wi 11 not be overtaxed as a result of futul-e development. Please see the hydrological section for a further explanation. Trai ler Courts. The trai ler court~, in Basin 2 anc 3 have been bui It Sc) t"--Jc:;t they have brought hazard upon them,.elves. The channel al ignment has been moved significantly from historica; cor,ditions. It has also been constrictell as a result of varying degrees of fi 11 ing and si ltation. The trailers in the hazardous floodpiain ar€BS should be removed to preve"1 1055 of life. This area is particuiarly -dangerou~; ~,ince thefloods will probably occur with little warning bec~use of the rather quick hydrological response of the mountainous areas clbove.