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2004-07-01_REVISION - M1987064
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2004-07-01_REVISION - M1987064
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Last modified
6/15/2021 2:56:05 PM
Creation date
11/21/2007 9:32:18 PM
Metadata
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Template:
DRMS Permit Index
Permit No
M1987064
IBM Index Class Name
Revision
Doc Date
7/1/2004
Doc Name
Hydro-Logic Report and Proof of Publication
From
Frank Anesi
To
DMG
Type & Sequence
AM1
Media Type
D
Archive
No
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Hydrologic Study of the Sandco Reach, <br />Animas River Valley, La Plata County, <br />Colorado, 2004 <br />By Winfield G. Wright, Southwest Hydro-Logic <br />Abstract <br />The Sandco Reach ofthe Animas River has <br />been a location for in-channel gravel mining since <br />1986. As an alternative to in-channel mining, Sandco <br />plans to operate an ofl=channel gravel mining area <br />where the work will occur during the winter months of <br />November through March. A lake will be created as <br />the operation proceeds, and the lake area will be <br />enlarged by 2 acres per year for 20 years. The new <br />lake area may be converted to a conservation easement <br />when the work is completed. Concerns have been <br />expressed by regulatory agencies and citizens about <br />the hydrology of the Animas River in the Sandco <br />Reach. This report addresses concerns relating to <br />construction of the lake, hydraulics of the seasonal <br />river crossing, effects of different flow regimes and <br />floods on the channel and lake, and the effects of the <br />future use on water quantity, water quality, and <br />erosion. <br />INTRODUCTION <br />Because of the high quality of sand and gravel, <br />the Animas River channel and overbank deposits in <br />the northern part of the valley (figure 1) have been <br />utilized for many years by aggregate companies. The <br />sand and gravel from this area has supported the main- <br />tenance and development of La Plata County and the <br />City of Durango. Much of the gravel mining has <br />occurred as in-channel operations under the hypothesis <br />that the gravel would be replenished each year by high <br />altitude snowmelt runoff from the San Juan Moun- <br />tains. Since about 1999, there has been a recurring <br />drougfitin Colorado and throughout the western <br />United Slates; therefore, the annual snowpack has <br />been below average and snowmelt runotl'dischazges <br />have not been sufficient to transport large quantities of <br />sediment and replenish the gravel resources. Subse- <br />quently, the Animas River channel has exhibited <br />impacts from the drought. These impacts include <br />channel incision, bank erosion, possible lowering of <br />the water table beneath the valley floor, loss of riparian <br />habitat, reduced overbank flood depths near the gravel <br />pits, and increased overbank flood depths farther down <br />the valley (Gillam, 2003). <br />As an alternative to the in-channel gravel <br />mining, Sandco, Ina plans to develop an off-channel <br />sand and grave( resource where the work will occur <br />only during the winter months, a lake will be created <br />from the gravel mining, and the lake will be enlarged <br />by 2 acres per year for 20 years. The new area may be <br />converted to a lake and wetland conservation ease- <br />ment when the work is completed. <br />There generally has been approval of the oti <br />channel gravel mining concept because i[ does not <br />directly impact [he channel and riparian areas, and <br />upon completion the lake will provide wildlife habitat <br />and open space for parks and recreation. Concerns <br />have been expressed by regulatory agencies and citi- <br />zens relating to the reclamation of the historical use <br />area, hydrology of the Animas River reach, construc- <br />tion of the lake, hydraulics of the seasonal river <br />crossing, effects of different flow regimes and floods <br />on the channel and lake, and the effects of the future <br />use area on water quantity, water quality, and erosion. <br />This report addresses the above concems as best <br />as possible using available data. No new data were <br />collected related to the hydrology, climate, or riparian <br />habitat. New interpretations ar'e provided in this report <br />including hydraulics of the seasonal river crossing, <br />modeling of the river reach to simulate different flow <br />>~ Southwest Hydra-Logie t <br />W ~__,. <br />
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