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CAPACITY UTILITY Pond 4) are developed from the Stage Storage Data on the As-Built. With •
<br />regazd to a 10-yeaz, 24-hour precipitation event, the design sediment .storage volume is 0.04 acre
<br />feet, between elevations 83.5 and 83.66. Peak Settleable Concentration of pond discharge is
<br />demonstrated at 0.00 mUl (< 0.50 mUl criteria). The peak stage is 86.04 (below the 90.0
<br />elevation of the emergency spillway. There would be no discharge over the emergency spillway.
<br />Cleaning of sediments from the pond is scheduled when 60% (0.024 acre feet) of the design
<br />sediment storage is occupied, a maintenance sediment elevation of 83.6 (83.596, interpolation
<br />between 83.50 @ 0.0 and 83.66 @ 0.04). The peak stage from a 25••yeaz, 24-hour precipitation
<br />event is 86.34. There would be no dischazge over the emergency s~~illway (invert elevation of
<br />90) from a 25-year, 24-hour precipitation event. As there is no flow (at the design criteria storm)
<br />over the emergency spillway, there is no requirement for riprap pl•otection of the emergency
<br />spillway crest or exit channel. Pond configuration is summarized and existing riprap (no
<br />specifications) is shown in the figure titled Sedimentation Pond 004 Supplemental Information,
<br />revised 5/6/96. Designs of ditches 4Na and 4Nb are presented under Pazagraph 7-7.
<br />7-6 Pond 005
<br />The SEDCAD+ Version 3 demonstrations appropriate to Pond 005 are
<br />C:\SEDCAD3\CR\PNDSREV4, Date 04-30-1996 Time 12:40:49 (10-yeaz, 24-hour precipitation
<br />event) and Time 12:41:50 (25-yeaz, 24-hour precipitation event). Tt~e steep east- and southeast-
<br />facing slopes of the Barren Ridge Area (see Map 8) drain to Pond 005 via Ditches SNa, SNb,
<br />SNc, SSa, and SSb. Watershed definition is based on degree of slopes. The steep watersheds aze
<br />characterized by repetitive terraces and benches. Pond 005 configuration is taken from the
<br />Sedimentation Pond As-Built, Pond 005, date 7-7-91, Rev. 1. Additional as-built configuration •
<br />detail concerning weep holes in the primary riser aze shown on drawing Sedimentation pond 005
<br />Supplemental Information, revised 5/6/96. Basin capacity information and curve (SEDCAD
<br />BASIN CAPACITY UTILITY, Pond 5) are developed from the Stage Storage Data on the As-
<br />Built. With regard to a l0-yeaz, 24-hour precipitation event, the desi,;n sediment storage volume
<br />is 0.07 acre feet, between elevations 92.0 and 92.42. Peak Settleable Concentration of pond
<br />dischazge is demonstrated at 0.00 mUl (< 0.50 mUl criteria). Bed scour is not likely to develop.
<br />Sediment deltas form at pond inlets and taper rapidly towards the di~;tant primary spillway. The
<br />peak stage is 98.00. There would be no discharge over the emergency spillway (98.5). Cleaning
<br />of sediments from the pond is scheduled when 60% (0.042 acre fret) of the design sediment
<br />storage is occupied, a maintenance sediment elevation of 92.24 (interpolation between 92 @ 0.00
<br />and 92.42 @ 0.07). The peak stage from a 25-year, 24-hour precipitation event is 98.76. There
<br />is no dischazge over the emergency spillway from a 25-yeaz, 24-hour precipitation event.
<br />Pond 005 configuration is summarized and existing (as-built) riprap (no specifications) is shown
<br />in the figure titled Sedimentation Pond 005 Supplemental Information, revised 5/6/96. Designs
<br />of ditches SNa, SNb, SNc, SSa and SSb are presented under Pazagr.3ph 7-7.
<br />7-7 Ditches
<br />The embankment side of triangulaz road ditches are designed with :ideslopes of 2 horizontal to
<br />1 vertical (2H:1V), others at 3H:1V. Trapezoidal ditches with riprap aze analyzed at 3H:1V side
<br />slopes and 6-foot minimum (a SEDCAD+ Simons/OSM requirement) bottom widths. Ditch 2Na
<br />is analyzed with loam substrate. Ditches 2Na, 2S, 252b, 2S2c, 3Na, 3N1, 3N2, 35a, 3Sc, 35d,
<br />4Na, and 55a aze analyzed with Cobble and Shingle substrate as residual armor in the ditch. •
<br />Ditches 251, 2S2a, and Ssb are provided with checkdams (as required) to arrest ditch erosion,
<br />and aze modeled with a stable (nonerodible) substrate. Ditches 3Nb, 3Nc, and 3S6 were designed
<br />7-$ 8 May 1996
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