Laserfiche WebLink
classified as ranaeland for domestic livestock and wildlife <br />use. Colowyo maintains a policy of no domestic livestock <br />grazing within the permit area, resulting in increased <br />vitality of herbaceous and woody plant species: Annual <br />revegetation monitoring "indicates a reasonably diverse, <br />successful establishment of desirable perennial grasses and <br />forbs, as well as the expected number of annual grasses and <br />forbs". Lastly and most importantly, Colowyo has been the <br />recipient of the Colorado Mining Association, Coal Mined Land <br />Reclamation Award or Honorable Mention, Large Surface Coal <br />Mine, for the years 1983-1988, and 1991. The award is given, <br />"For an outstanding compliance record and <br />continued exemplary reclamation performance". <br />All factors combined lead to a minimum of a good rangeland <br />classification. <br />As per Colowyo's mine permit, page 2.04.8-1, Climatological <br />Information, the climate of Northwest Colorado is classified as <br />semi-arid. A major factor affecting runoff, especially in a semi- <br />arid climate, is evapotranspiration (ET). ET is a major <br />abstraction or loss to precipitation, with runoff equal to <br />precipitation minus all losses. Actual measurements of ET in <br />watersheds surrounding the Colowyo mining area (See Colowyo Permit, <br />page 2.04.7-50) show that the "ET ranges from 95.6 to 98.6$ of <br />.;• total precipitation indicating that nearly all of the precipitation <br />.- is evaporated in place" which means that "runoff values for these <br />watersheds are extremely low and range between 1.3$ and 4.2$ of the <br />precipitation falling on the watersheds°. Quite simply, <br />precipitation falling onto a semi-arid watershed does not result in <br />appreciable runoff. <br />Discussions with Dr. Richard Warner further explained the <br />relationship between the Curve Number (CN), Antecedent Moisture <br />Condition (AMC), and Evapotranspiration (ET). Dr. Warner is the <br />author of SEDCAD and co-author of Applied Hydrology and <br />Sedimentology for Disturbed Areas. Attending Dr. Warner's SEDCAD <br />course last year afforded the opportunity to discuss with him in <br />quite some detail, the SEDCAD modeling of the Colowyo Mine. <br />Dr. Warner explained that the comprehensive list of Curve <br />Numbers given in SEDCAD, or obtained from the Soil Conservation <br />Service (SCS), refer to AMC ZI. AMC is defined by SCS as "an index <br />of watershed wetness" with AMC II defined as "the average <br />condition". Dr. Warner referred me to pages 82-84 in Applied <br />Hydrology and Sedimentology for Disturbed Areas where it says <br />"Antecedent condition I is used when there has been little rainfall <br />preceding the rainfall in question and condition III is used when <br />there has been considerable rainfall prior to the rain in <br />• question°. Dr. Warner further explained that in the semi-arid <br />southwest, weather fronts are such that return periods for <br />'~::% successive storms occur only every 72 hours. The time period <br />between rainfall events allows ET to occur (as described above), <br />