![]() The EGL for the storm drain design flow must at no time or location exceed the manhole rim or inlet throat elevation. These include the calculation of energy grade lines (EGLs) and hydraulic grade lines (HGLs) indicating all hydraulic losses due to friction, junctions, and other structures and phenomena. The design of pressure-flow, or surcharged, storm pipes is allowed under certain restrictions as specified in this chapter. 40-08 (§ 1002), 3-19-08) 28.40.030 Storm drain design criteria – Allowable capacity.Īs described in GJMC 28.40.010 and 28.40.160 through 28.40.190, a storm drain is designed to convey up to the entire design storm for all sub-watersheds tributary to it. GJMC 28.40.020 through 28.40.060 present certain parameters relating to the design and construction of storm drain systems in Mesa County. (d) Peak runoff values are found using the methods set forth in Chapters 28.24 and 28.28 GJMC. ![]() (2) Locations where the standard allowable major storm street capacities do not apply, such as negative slopes outside the curb but within the right-of-way. (1) Locations where street flow is not in the desired direction and there is no other feasible drainage solution (such as closed basins – natural ponding areas). (c) Occasionally, inlets and storm drains must be sized to convey the entire major storm event flow. This is discussed further in GJMC 28.40.160 through 28.40.190. This could be the difference between the major storm peak runoff and the allowable street capacity for the major storm, or it could be the difference between the minor storm runoff and allowable street capacity for the minor storm. Storm drains shall be sized to carry the maximum difference between street capacity and peak runoff for any given design storm. In some cases, however, street inlets discharge their intercepted flow to drainage facilities other than a storm drain (e.g., a drainage channel). As discussed in Chapter 28.44 GJMC, the first inlet will either be located at the point where street flow from the design storm exceeds street capacity for that storm (on-grade inlet) or where there is a vertical sag in the street (sump inlet). This means the upper end of a storm drain branch will usually be located at the first inlet encountered by runoff in a given sub-watershed. (b) Typically, storm drains are sized to convey the peak runoff from the minor storm in excess of the contributing street flow capacity. The design of a storm drain system is dependant on topography, street rights-of-way and drainage easements, the need to convey flows from multiple locations, existing and proposed structures and utilities, outfall locations, local hydrology, and regional and local design criteria. However, water may also enter the system via grated area inlets, culvert-type inlets (typically for the conveyance of drainage-channel flow into the drain), pump stations, or other entry points. The most common method for the introduction of water into a storm drain is the street inlet, discussed in Chapter 28.44 GJMC. (a) Storm drains are used to convey runoff in locations where streets or other drainage facilities exceed their designated capacity or are otherwise unable to drain. 28.40.030 Storm drain design criteria – Allowable capacity.Ģ8.40.040 Storm drain design criteria – Allowable velocity.Ģ8.40.050 Storm drain design criteria – Pipe roughness.Ģ8.40.060 Storm drain design criteria – System layout.Ģ8.40.180 Preliminary/final storm drain design.Ģ8.40.190 Example design application.
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