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Introduction <br />L SHBIRRIGATED ALLUVIAL-VALLEY FLOORS <br />- A'Reconnaissance of Their Properties and Occurre e on <br />Coal Resource Lands in The Interior Western t tates* <br />March 1977 <br />John E. Rardawa <br />Chief, Research & Applica <br />Dan B. Kimball <br />Environmental Protection T. •ologist <br />Shirley F. Lindsay <br />Terrestrial Biologist <br />Jack Schmidt, Larry Erickson <br />- Consulting Geologists <br />U. S. Environmental Protection Agency, Region VIII <br />Denver, Colorado <br />Concern for Alluvial Valley Floors <br />and the Impacts of Surface Coal Mining <br />Concern has been expressed regarding the long -term impacts of surface coal mining <br />on lands in the western United States currently or potentially useful for agriculture. <br />Part of this concern bears on disruption of these lands used by wildlife. I. pe tz icu- <br />la3F there- are- ques.r+nric rpgat :ding - .th : .poteatiaL-impact -•of.= coal *•extraction in._cartain,,,, <br />lowland iteas`of" the - arid• - 'West - where - shalla r ground water•- and /or_.soil:moisture. <br />is'" ad" egsiatr ilb°support^'grOWtrof^'grasaea- •and- forbe the• - dry „anogtha. These <br />land areas, located along drainage channels and referred to recently as ' -' alluvial <br />valley- flooxs4.(National Academy of Sciences, 1974), azer- most rtant -iri- semi -arid <br />.._. ” um eneblingcvegetation to <br />nemt.imme.azarahawmilevismarehseefft4aewzacinfeSclam Apparently, soil moisture, ° and <br />perhaps some near - surface ground water, subirrigates the vegetation. <br />The character of the vegetation is a function of both depth to water table <br />(depth to saturated zone) and quality of the soil moisture and ground water. The <br />depth to water table, as well as seasonal variations in this parameter, may be criti- <br />cal in determining the composition of the vegetation. For example, if the saturated <br />zone is sufficiently near the ground surface to permit capillary migration of ground <br />water to the surface, subsequent evaporation may cause accumulation of salts. Under <br />such conditions, the vegetation nay be comprised principally of salt- tolerant species, <br />such as alkali sacaton (Sporobolus airoides). Similarly, the configuration and <br />moisture retention characteristics of the capillary and remaining unsaturated zone <br />may be the most critical elements of the ground water system that supports vegeta- <br />tive communities in the lowland areas. However, no one has yet reported on the <br />essential functions critical to sustained growth of vegetation in these areas. <br />Alluvial valley floors are used for grazing and for production of hay. Both <br />domesticated and wild animals are attracted by the more vigorous vegetative growth <br />and the presence of surface water in these lowland areas. The alluvial valley floor <br />areas include the principal surface water accumulation points, as well as points of <br />ground water recharge and discharge. <br />Some vegetative <br />* This article is based on a draft report being developed by the authors. However, <br />no official support or endorsement by the Environmental Protection Agency or any <br />other agency of the federal government is intended or should be inferred. <br />7 .1 Ca <br />5620. <br />{) 4'1 <br />F <br />`4 . 7 <br />I . ' t <br />