FLOOD01607 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I CENTRAL CITY MASTER DRAINAGE STUDY 26 SECTION 5. NEVADA GULCH DRAINAGE 5.1 General CWCB (1987) modeled Nevada Gulch as a single 704 acre basin (Figure 1.1.1). Discussion in this section shall identify the major basin as well as a small tributary to Nevada Gulch, Spring Gulch. No opportunity exists to develop a detention site of significant size on Nevada Gulch as was possible with Eureka Gulch. Consequently, drainage improvements are limited to improvements to existing inlets, area drains and mine tailing stabilization. Spring Creek drains 160 acres (23 percent of the entire Nevada Gulch basin) and has mine tailings throughout its entire reach. Tailings in several locations extend into the stream itself. Climatic events have historically resulted in extensive amounts of sediment being deposited in the downtown area of Central City. This section discusses methods that mitigate sedimentation problems. 5.1.1 Existing Drainage Facilities The main stem of Nevada Gulch has been extensively denuded of vegetation. Water from Nevada Gulch currently enters a box culvert and is conveyed under mine tailings (the Free Parking Lot) and the Big Triangle Parking Lot into Gregory Gulch. When box culvert inlet capacity is exceeded, water would flow down Nevada Street, across the Big Triangle Parking Lot and eventually enter Gregory Gulch via Main Street and Spring Street. Spring Gulch contributes minor amounts of water compared to Nevada Gulch but apparently contributes extensive amounts of sediment to downtown Central City. A series of pipes ranging .from 36-inch to 72-inch exists to convey flows from this small drainage into those from the main stem of Nevada Gulch, Inlets should be designed to convey greater amounts of water through :this pipe system to lessen the impact of drainage and sediment from Spring Gulch. 5.1.2 Proposed Drainage Facilities It is estimated that the 100-year flood can be conveyed to Gregory Gulch with no overflow onto Nevada Street by improving the inlet conditions for the existing structure from the main stem of Nevada Gulch. If overtopping c6nditions were to occur, degradation of the Nevada Street roadside swale can be lessened by a series of drop inlets. For Spring Gulch, increased conveyance of flows can be realized by a series of drop inlets along Spring and Roworth Streets,. The problem of sediment from tailings may best be addressed by analyzing the tailings to determine whether native grasses can be established. Attendant to establishing grasses, control of flow :a ~ HydroDynamics Incorporated