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3.5.4(Z). <br />DRAINAGE MANUAL <br />,issan TT99 <br />r1 <br />I <br />II i <br />iI <br />I ' ! 1 , I ' t` <br />10 <br />Duration of Rainfall or Trrne of Concentration {rninute5} <br />August 30, MOO <br />Film re3.4 Zone 1 Southern Minaefinta Rainfall Intensity - Duration - Frequcnev (IDF) Curves <br />Impervious Surface: The portion of the buildable parcel which has a covering which <br />does not permit water to percolate into the natural soil. Impervious surface shall include, <br />but not be limited to, buildings, all driveways and parking areas (whether paved or not), <br />sidewalks, patios, swimming pools, tennis and basketball courts, covered decks, porches, <br />and other structures. Open, uncovered decks are not considered impervious for the <br />purposes of this ordinance. The use of patio blocks, paver bricks or class 5 gravel <br />material are considered impervious surfaces as a majority of water runs -off the surface <br />rather than being absorbed into natural soils underneath. Some exceptions to these <br />conditions may include paver blocks or pavement systems engineered to be permeable <br />with the underlying soils suitable for infiltration. <br />Infiltration Basin: An impoundment where incoming storm water runoff is stored until <br />it gradually infiltrates into and through the soil of the basin floor. <br />Infiltration Trench: A conventional infiltration trench is a shallow, excavated trench <br />that has been backfilled with stone to create an underground reservoir. Storm water <br />runoff diverted into the trench gradually exfiltrates from the bottom of the trench into the <br />subsoil and eventually into the water table. An enhanced infiltration trench has an <br />extensive pretreatment system to remove sediment and oil. It requires an on -site <br />geotechnical investigation to determine appropriate design and location. <br />Section XI <br />October 21, 2015 Page 77 <br />