FLOOD02174 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I 4 of drainage channels for a highly urbanized watershed. The chan- nels are poorly suited for this service, and as a consequence, the basin is subject to a major damage potential in periods of even moderate rain storms. the two gulches were the only major drainage pourses prior to urbanization. The additional tributaries which existed histori- cally presumably were small and generally undefined, and ran gen- erally parallel to the major channels in an easterly direction. The Dry Gulch watershed consists of approximately 3.7 square miles, and is relatively long and narrow. Dry Gulch itself flows generally eastward to its confluence with Lakewood Gulch near 10th Avenue and Perry Street. Lakewood Gulch then carries the Dry Gulch runoff approximately one mile to its confluence with the South Platte River in Denver. North Dry Gulch is the only major tributary to Dry Gulch; it drains a sub-basin of about l.l square miles and joins Dry Gulch east of Harlan Street. The urbanization of the basin has included the superimposing of a street system over the drainageways. The gulches were not significant enough to cause the streets to be built around them, so they were generally replaced by culverts where the streets crossed them. The sizes of the culverts were selected haphaz- ardly, and invariably caused a restriction in the capacity of the channel. Since most of the larger streets were constructed on slight fills or embankments, they frequently represented drain- age "i1ivides" which diverted flow from its natural course. In some cases, these diversions are of major proportions, and have led to flooding nuisance in locations which are not directly adja- cent to the channels. The soils of the watershed are comprised primarily of the Piney Creek Alluvium in the channel beds and of Loess and Verdos Alluviums in the remainder of the basin. The Loess and Verdos Alluviums are generally described as having moderate to high vertical per- meability. The Loess has very low lateral permeability. The static water table ln the area is normally five to ten feet below the surface. This study addresses the Dry Gulch Channel from Lakewood Gulch to Simms Street, a length of 5.7 miles, and the North Dry Gulch Channel from Harlan Street to Dover Street, a length of l.8 miles. An analysis of current and older topographic maps indicates that Colfax Avenue has created major disruptions of flow and transfer of drainage problems at four locations: Miller Street, Garrison Street, Balsam Street, and Pierce Street. North Dry Gulch reaches the intersection of Colfax Avenue and Balsam Street and diverges, with a portion flowing eastward on each side of Colfax. The split is large enough that the flow on the south side of Colfax has been designated Colfax Gulch, for the purpose of identification. Colfax Gulch flows from Balsam Street to Pierce Street in the block south of Colfax.