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TNF 903 N <br />SF-3 <br />SB-3,. <br /> <br />S&2•~ ~ RR-3 W E <br />SF-2- <br /> $ <br />V-3• <br /> <br />Weather St ion <br />RR-2" ' <br />' V-2 <br />~•^~ -1 <br />- V-1 <br />SR-i; <br /> N -Forest Rmd• <br /> / <br />f V - S6em'a <br /> • - RuroR Samplers <br /> SF - SMiment Ferae <br /> SB - SetlGrg Bacin <br /> RR - Riptap <br />RR-1` V Vegetatlon <br />Figure 1. Eaperhnental design and IIeld layout for the 1Lskegee study. <br />Tahle 1. Recommended spacing for tum- <br />outditches and broad lased dips. <br />Road Gradient 'IYtm-Out Ditch[a] Broad-Based IHpi~] <br />n Tl <br />5 55 55 <br />10 43 43 <br />15 38 39 <br />tort Alabama Porosuy Commission, 1993. <br />rot Hewled and Douglass, 1968. <br />Crowned Forest Road whh D'dches <br />Inlet Sanpling <br />Treatment Area <br />Outlet Sempling <br />Erosion Stakes Runoff <br />0 0 o Dlvarsion <br />0 0 o Oam <br />1 micron Fitter <br />Sags <br />Figure 2. D(agram or individual test area for the 15rskegee study. <br />where <br />V =runoff volume (m3) <br />A =drainage area (mz) <br />d =depth of rainfall (m). <br />Each basin's design dimensions were 3.5 m x 3 m x 1 m, <br />with a storage capacity of 11 m3. Rip-rap ditch treatments <br />consisted of No. 1 coarse aggregate applied to a thickness of <br />31 cm and to a length of 3 m from the ditch outlet. Sediment <br />fences, 3 m in length, were placed perpendiculaz to turn-out <br />ditch outlets for all sediment fence treatments. <br />Sediment transport from the road prism was measured <br />using two runoff samplers at each tum~ut ditch stmcttue <br />located at the inlet and outlet of the mitigation treatments. <br />Composite runoff samples were collected for each runoff <br />event, and suspended sediment was determined by gmvimet- <br />ric filtration. Filtering accomplished by each associated <br />treatment was determined by comparing inflow and outflow <br />runoff concentrations. <br />Sediment delivery downslope onto the forest floor was <br />also investigated by measuring the quantity of sediment <br />exported [o the forest floor downslope of the mitigation <br />treatments. A diversion dam was located below each <br />mitigation treatment to direct runoff into 1-micron filter bags <br />(fig. 2). Filter bags were periodically collected, dried, and <br />weighed. The collected sediment indicated the quantity of <br />sediment that would have been exported into filter strips <br />below each turn-0ut treatment. Erosion stakes were installed <br />above the diversion dams. Forest floor elevation changes <br />were determined from erosion stakes and were used to <br />estimate the weight of sediment deposited on the forest floor <br />upslope of the filter bags. Total exported sediment was <br />determined as a combination of sediment collected in filter <br />voi. as(a): xxx-xzx <br />