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<br />e' <br /> <br />-,- - <br /> <br />----. --.-..........,_. .-.~~- <br /> <br />Table IV-6 <br /> <br />FACTORS FOR ALLOWABLE INLET CAPACITIES <br /> <br />Condition <br /> <br />Allowable <br />Capacity Factor <br /> <br />Inlet Type <br /> <br />Sump <br />Sump <br />Continuous Grade <br />Continuous Grade <br />Continuous Grade <br /> <br />DIO-R <br />Grated <br />DIO-R <br />Longitudinal Bar Grated <br />Transverse Bar Grated or <br />Longitudinal Bar Grated <br />Incorporating Transverse Bars <br /> <br />50% <br /> <br />80% <br />50% <br />75% <br />60% <br /> <br />F. Detention <br /> <br />Detention of storm water runoff offers two primary benefits <br />to entities involved in storm water control. Temporary storage <br />can significantly reduce peak flows with a consequent reduction <br />in the size of downstream main line facilities. The other <br />significant benefit which can be realized is in the reduction <br />of debris and sediment loading to streams. <br /> <br />---------~~ <br />Master drainage basin plans should include an economic <br />analysis of the use of detention and similar structural controls <br />to attain an optimum system design. Such an analysis must <br />carefully examine the continuing maintenance costs associated <br />with these types of facilities. Combining parks and open space <br />with temporary storage facilities can result in cost savings <br />for land requirements. <br /> <br />On-si te detention shall be used in areas where, through <br />zone changes or physical alterations, an increase in runoff <br />would overload downstream facilities. Roof top ponding and <br />parking lot detention are typical methods of accomplishing <br />detention on a small scale. <br /> <br />Sizing of detention facilities should be done with major storm <br />(100 year) runoff as a minimum. For larger structures (See <br />Part II) criteria events may be dictated by the State Engineer. <br />The basic procedure to size a facility is as follows: <br /> <br />1. Calculate incoming flood hydrograph (See Section III). <br /> <br />2. Construct a stage-discharge curve (Section IV-C). <br /> <br />3. Calculate a stage-volume curve. <br /> <br />4. Determine the average inflow volume for a time increment 6t. <br /> <br />5. Estimate pond stage from stage-volume curve. <br /> <br />52 <br /> <br />~, <br />'I <br />I, <br />lid <br /> <br />I: <br />'1 <br />I) <br />!; <br />!! <br />.J <br />". <br /> <br />'.I <br /> <br />,.; <br /> <br />'I <br />II <br />Ii <br />r' <br />"" <br /> <br />~j <br />,~ <br />t.. <br /> <br />I:, <br />,: <br /> <br />