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collected from many streams (figure 13). Using the
<br />computations for culvert design at low flow, the outlet
<br />velocity from the 8 culverts during discharge in the
<br />Animas River of 225 ft3/sec would be about 6 ft/sec
<br />(182 cm/sec). Referring to the Hjuls[rom diagram
<br />(figure l3), small particle sizes could be eroded.
<br />Pebbles and cobbles may no[ be eroded at these outlet
<br />velocities. Using the culvert calculations for
<br />maximum culvert capacity up to the tops of the
<br />culverts (figure 5), [he outlet velocity for 510 ft3/sec
<br />would be about 8 ti/sec (244 cm/sec), and nearly all
<br />sediment sizes shown in the Hjulstrom diagram would
<br />be eroded and transported. From this analysis, using
<br />the largest sizes of road bed construction (larger than
<br />I00 mm diameter) would possibly prevent the erosion
<br />and transport of sediments from the seasonal road
<br />crossing downstream along the Animas River.
<br />SUMMARY
<br />The historical use area of the Dalton Pit of the
<br />Sandco in-channel gravel mining area will be
<br />reclaimed to near as possible to the natural channel
<br />wnfigurations. High flow snowmtelt runoff in the
<br />Animas River, which have not occurred for the past
<br />few years, will help to replenish the gravels in the
<br />reach.
<br />The future use area will create a lake ai the rate
<br />of about 2 acres per year; areas disturbed on an annual
<br />basis will be reclaimed as work progresses. Upon
<br />completion of the project, the lake will be about 44
<br />acres. The lake may be converted to aquatic and
<br />wetland conservation easements after the area has
<br />been reclaimed. The lake will be constructed for
<br />consideration of the wildlife and aquatic habitat. The
<br />seasonal river crossing of 8 culverts will be able to
<br />sustain a river discharge of 510 ft3/sec up to the tops of
<br />the culverts, and 838 ft3lsec before the road overflows.
<br />The culvert crossing should be constructed out of the
<br />largest size material as possible, grain sizes greater
<br />than cobbles, in order to prevent erosion and transport
<br />of sediments downstream.
<br />Modeling of the Sandco Reach of [he Animas
<br />River using HEC-RAS indicated that the 100-year
<br />flood of 24,600 ft /sec will not exceed the bank eleva-
<br />tions on the east side of the river where the future use
<br />area will be constructed.
<br />Evaporation depletions from the future use lake
<br />would total about 96 acre-ft per year after completion
<br />of the project in 20 years. The (low quantities of this
<br />evaporation would be about O.13 ft3/sec, which would
<br />not be noticeable, and might not be measurable by
<br />conventional methods in the Animas River. There-
<br />fore, aquatic life and endangered fish species would
<br />not be impacted by this small quantity of flow deple-
<br />tion.
<br />REFERENCES CITED
<br />Bames, H.H., Jc, 1967, Roughness characteristics of natural chan-
<br />nels: U.S. Geological Survey Water-Supply Paper 1849.
<br />Blair, R.W., Jr., Yager, D.B., and Church, S.E., 2002, Surficial geo-
<br />logicmaps along the riparian mne of the Animas River and ¢s
<br />headwater tributaries, SilveAOn [o Durango, Colorado, with
<br />upper Animas River watershed grndien[profiles: U.S.Geolog-
<br />ical Survey Digital Data Series DDS-71, Version L0, CD-
<br />ROM.
<br />Church, S.E., Fey, D.L., Drouwers, E.M., Holmes, C.W., and Dlair,
<br />R.W., Jr., 1999, Determination otprc-mining geochemical con-
<br />ditions and patcoccology in the Animas River watershed, Colo-
<br />rado: U.S. Geological Survey Opcn-File Report 99-0038, 16 p.
<br />Gillam, M.L., 1998, Late Cenozoic geology and soils of the lower
<br />Animas River valley, Colorndo and Ncw Mexico: unpublished
<br />Ph.D Dissertation, University oCColorndo, 477 p.
<br />Gillam, M.L., 2003, Le0cr report to dte U.S. Amry Corps of Engi-
<br />neers, November 28, 2003, 17 p.
<br />Penman, H.L.,194$ Natural evaporation from open water, bare
<br />soil and grass: Proceedings oCthe Royal Society A, vol. 193, p.
<br />120-I45.
<br />U.S. Army Coms of Engineers, 2002, HEC-RAS River Analysis
<br />System, Users Manual, Version 3.1, November 2002: U.S.
<br />Atmy Corps of Engineers, Institute for Water Rcsoun:es,
<br />Hydrologic Engineering Center, Davis, Calif.
<br />Hydrologic Study at the Sandco Reach, Animas River Valley, La Plata County, Colorado, 2004 20
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