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<br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />-6- <br /> <br />The improved channel is a two-stage design consisting of a low-flow channel with a capacity of <br />approximately 40 cfs that meanders within a grass-lined major channel, which is designed to convey <br />the lOa-year discharge of 3,650 cfs. The low-flow channel (Figure 3) combines a concrete invert with <br />large boulders placed along each side. The boulders were placed with top surfaces level and as close <br />together as possible. Voids between the boulders were filled with smaller rock. Granular bedding <br />material placed behind the boulders enables the channel sides to act as a reverse filter that drains the <br />soils in the bottom of the major channel following large storms, This allows the grass lining to remain <br />stable for mowing and maintenance equipment <br /> <br />25FT, 10.B mlBOULDERS PLACED <br />VilTH TOP S~R,ACES LEVEL AND AS <br />CLOSE TOGETHER AS POSSIBLE <br /> <br />SIULL RIPRAP TO FILL VOIDS <br />BETWEEN BOULDERS, np. EACH <br />SIDE,\ _ <br /> <br />2% lAIN. <br />. <br /> <br /> <br />~ <br /> <br />Bn,12.4m) <br />2 FT. 10.6 ml <br /> <br /> <br /> <br />.~ <br /> <br /> <br />A ''.il' <br />5 INCH (12.7 em) <br />THICK CONCRETE <br />INVERT <br /> <br />GRANULAR <br />BEDDING <br />WATERIAL <br /> <br />Figure 3 Low-flow Channel Section <br /> <br />The concrete invert allows efficient sediment transport to prevent potential aggradation related to the <br />flatter slope of the improved channel. A lO-foot-wide concrete maintenance road and recreational <br />path traverses the entire length of the channel. <br /> <br />The drainageway improvements are enhanced by abundant landscaping, including irrigated sod along <br />the channel corridor and extensive tree and shrub planting, A unique feature of the projec: is the <br />installation of landscape planting in riprap slopes. Sections of 24-inch-diameter polyethylene pipe <br />were utilized for shrub planting wells and concrete manhole sections were used for tree wells, The <br />planting wells were placed with the rip rap and then backfilled with a combination of rock and backfill <br />material, enabling the wells to integrate with the surrounding riprap. The spreading shrubs and tree <br />plantings are served by a drip irrigation system and, when mature, will soften the structural <br />appearance of the riprap slopes, Besides improving the appearance of the banks, the plant species <br />were selected to work with the hydraulic function of the channel. For example, willows have been <br />