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11-8 Basin 9. The geological character of Basin 9 is the same as Basin 11 with the same infiltration rate of two thirds of an inch per hour. The basin is almost entirely developed with the e)(ception of some open fields near Kipling Street. The primary problem in this basin is that Lena Gulch has been con- stricted to such a severe degree that any significant flow floods an extremently wide area north of the stream. For example, the Red Barn Store near 38th Avenue and Hi ller Court is actually bui lt over Lena Gulch. The natural draina<Jeway has been replaced by a 5 foot diameter concrete pipe which daylights to the east in about a 4 foot square box culvert. The entrance conditions to the conduit are extremely poor. The four smal: diameter pipes that keep debris from enterin<J the pipe also restrict most of the water flaw. Also of note in this basin was the heavy amount of debris and trash in and about the gu 1 ch. I t was apparent that in severa 1 I ocat ions residents had considered the gulch to be an amenity to the community only because it is a convenient place to dump thei r trash. Basin 10. Basin 10 is slightly mor'e d'verse geologically with struc- tures ranging from loess, a sandy si It. to claystone formations and colluvium. The upper portion of this basin is flat, encoura<Jing infi ltration and detention of rainfall.. Infi ltration rates were approximated to be moderate, about 0.9 inches per hour. Care should be taken in future development to prevent any develop- ment which would cause any increases in flooded area which occurs presently near 28th and Kipling. Basin 11. The small area below Kiplin,! Street is the area tributary to Lena Gulch immediately before its confluence with Clear Creek. The southerly portion of the basin is quite steep and, as a result, the flatter northern portion along Lena Gulch and Clear Creek is more subject to flooding. It is apparent that the stream alignment has been moved in the past 50 years to its present east-'west di rection This has resulted in a flat streambed that has silted to such a degree that the channel capacity is qui te low. The runoff from this basin is not significant in comparison to the upstream flow from Lena Gulch. Development, however', should care- fully consider the floodplain areas of both Lena Gulch and Clear Creek. Summary. Table 11-2 summarizes various physical parameters for each of the basins for present and future conditions. The referenced steady state infiltration rates are usually reached within a ten to twenty minute period after the beginning of the design stonn..