PERMFILE64548

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: & Subsidence Effects on Vegetation Report dated June 1992 ‎(Fsh Crk AVF)‎
• Section_Exhibit Name: EXHIBIT 07c FISH CREEK AVS/STREAM STUDY MONITORING PROGRAM
• Media Type: D
• Archive: No

/wnt 1991 Cyprwr TCC • SwLsrdrnre E/jau on Vegec.tion ~ 3
• total vegetation cover and big bluegrass accounts for approximately 24 pecan[ of the total.
Mean total production in this type (based on 1984 data) wu 149 gams per square meter. Shrubs
accounted for 59 percent of the total production and perennial gruses accounted for 25 percent.
The sagebrush/meadow type on the bottom-land hu a mean cover value that is 18 percent
grea[er and a production value that is approximately 98 grams per square meter higher than the
sagebrush shrubland type that occurs on [he adjacent uplands.
3.0 SUBSIDENCE EFFECTS
In order for any rubsidena effects to occur within the sagebrush/meadow vegetation type, the
subsidence would have to affect existing plant-soil-water relations for the existing vegetation
types. In theory, the system could be disrupted by either a decease in water availability, if the
subsidence caused a dewatering of the alluvial system, or an incense in the amount of water
available to [he plants if the subsidence were [o disrupt and impair existing flows and drainage
patterns. If either of these conditions were to occur on a long term buffs, vegetation on the
bottom-land area could be effected.
In the event the alluvial system were to be dewatered, the vegetation would likely change and
become more like the adjacent upland sagebrush vegetation type. Tota] vegetative cover in the
bottom-land could decrease by up to 20 percent and productivity could drop a maximum of 100
grams per square meter. The magnitude of these changes is based on the usumption that even
if [he bottomland area are dewa[ered, vegetation on the valley floor could continue to product
. u much biomass and provide az much cover u the adjacent upland vegetation. Information
from [he rubsidena (SubTerra/ACZ 1992, Exhibit 7B) and hydrology (Hydro-Geo
Consultants/ACZ 1992, Exhibit 45) reports suggest [hat undermining the alluvial valley floor
will not dewater the stream valley in the portions that are undermined. If the alluvial rystem
is not dewatered, there will be no significant changes in the existing vegetation.
If non-uniform rubsidena rerul[ing from undermining were to a disrupt drainage patterns, it
is possible that vegetation on the valley floor could become more mesic, the percentage of sedges
and rushes could incense, and the vegetation mould change to more of a wetland meadow [ype.
If this were to occur, vegetation parame[ers including [oral vegetative cover and mean
production would likely increase over current values. Information from the hydrology and
subsidence reports suggest that rubsidena rnuld minimally influence the stream gradient,
however "the dynamic character of Fish Creek, with a constantly changing channel cutting
through fine grained sediments, would facilitate rapid natural adjustments to any temporary
changes in streambed gradient" (Hydro-Geo Conrultants/ACZ 1992). If there are no changes
in the stream gradient and the associated alluvial deposits, there would likely be no significant
changes in the existing vegetation.
4.0 CONCLUSIONS
Depth to the Wadge coal seam, which underlies the designated Fish Creek AVF is
approximately 1,000 to 1,100 feet. Extraction of approximately 8.5 to 9.5 feet of coal will result
in projected rubsidena within the AVF area ranging from 0 to 48 inches. Subsidence will vary
• in magnitude over the average AVF width of approximately 500 feet and extend over a distance
of approximately 1,800 feet along the drainage axis.
ACZ /nc. ' P.O. Box IIIOt B ' Srwmbaot Spn'ng; Co%rada 80177 '[phone]