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I I I I I I I I I I I I I I I I I I I 20 III. HYDRAULIC ANALYSIS A hydraulic analysis was conducted of the existing and proposed drainage systems within the Planning Area. This analysis included the delineation of 100-year fl oodp 1 a in areas, detenni nati on of the capacity of exi sti ng storm- water facilities, and the sizing of alternative drainage systems. The Town of Ordway can be divi ded into three general basins, namely the east, central, and west basins. The general limits of these basins were pre- sented in the Hydrologic Analysis, Section II. These basins are drained within the Planning Area by a series of small open channels and/or small diameter storm sewers. Present residential and commercial areas are not ade- quately drained by the existing system alone, particularly in those areas i mmedi ate ly north of the rail road grade. A descri pti on of the exi s ti ng drainage system and floodplains follows: Existing Drainage Facilities Shown on Figure 6 are the existing drainage facilities within the Town of Ordway. Superimposed on Fi gure 6 is the 100-year flooded area \,hich has been identified as a result of the field work, hydraulic analysis and existing floodplain information. Several open channels exist and are being utilized for storm.tater con- veyance. The largest drainage facility is the Town of Ordway Ditch, which is aligned along the eastern right-of-way of Colorado Highway 71, and extends from approximately the railroad grade, north to 11th Street. This channel is operated and maintained by the Town of Ordway Ditch Company. The cost for this service is assessed to the Town on an annual basis, and according to the cost for the work accomplished in that same year. This facility was assumed to have a perpetual use for stornwater only. Irrigation laterals and subsurface drains exist within several areas of the Town, and were observed to be functioning. These facilities offer little or no stormwater conveyance. Often times sub-drain and irrigation systems can aggravate minor flooding and cause deterioration to drainage facilities which eventually receive the groundwater or irrigation return flows. For the pur- poses of this hydraulic analysis, irrigation and subdrains were assumed to be full at the time of a flood event.