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• this junction to help transport flow to the yard (sediment ponds) and away from <br />the pile. See the design drawings for details. <br />In addition to the main, central drain it is recommended that French drains be <br />constructed on both sides at 100-foot intervals for the 800 ft of reaches 2 and 3. <br />These French drains should consist of 4" perforated pipe centered in a bedding <br />zone 24" x 24", trenched into the natural surface. The bedding should be a well <br />graded gravel with a maximum rock size of/. ". The finger drains should extend <br />through the side of the underdrain filter liner and into the drain. laterally they <br />should extend across the valley floor to the breakpoint in the slope with the valley <br />side walls. <br />If at anytime during salvaging of topsoil or any other construction activity, a <br />spring or seep is encountered, an additional lateral French drain shall be installed <br />from the seep to the underdrain. It shall be constructed as described above. <br />The underdrain is wrapped in a porous filter cloth (designed to allow water to <br />enter but keep out fine sediment) and filled with rock. No more than 10% of the <br />rock may be less than 12" in size and no single rock may be larger than 25% of <br />the depth of the drain. Flow from the drain will enter the lower intercept channel <br />and subsequently be diverted to the ponds for settling. <br /> <br />r~ <br />U <br />January 199R <br />