|
<br />
<br />" .
<br />
<br />
<br />B246
<br />
<br /> 100 l,.. <
<br /> . ,
<br /> ~ /~
<br /> 50 :- / .
<br />Z / -;
<br />-w 'o~ /
<br />. " /
<br />:i .1,0.- / ..;
<br />w ;
<br />-w 2.0 l-- ...;
<br />~.
<br />Z! I ,
<br />wO i I
<br />2" -l
<br />-~ l.O ::-
<br />Ow "
<br />~~ ~ "
<br /> ~
<br />0::; '"
<br />ww 0.5 r- ...;
<br />~. 0.4 !- l
<br />c.
<br />~w I
<br />-~ O,J[
<br />'"" l
<br />,,<
<br />w 02
<br /> / -
<br /> I, ,
<br /> /
<br /> oj' /
<br /> 0 .. .. " 100 125
<br />
<br />
<br />HYDROLOGIC TECHNIQUES
<br />
<br />f\)
<br />~
<br />=
<br />~
<br />
<br />The upland erosion and the channel erosion-sedi-
<br />ment transport factors are dependent on the other
<br />se,'en factors (table 1); therefore, high values for the
<br />two erosion factors should correspond to high ,'alues
<br />for the other snen. If the rntings do not check in this
<br />manner. the PSIAC sediment.,tion task force sug-
<br />gested that either special erosion conditions erist or
<br />the first seven factors in table 1 should be reevaluated.
<br />The numbers assigned to the factors are summed,
<br />and the total rating value is used to obtain a probable
<br />sediment )'ield ronge as shown in table 2.
<br />T)'pe of relief aud its associated vegetation WlIS de.
<br />lineated in each watershed by use of topographic maps
<br />and aerial photographs, and the percentage of the
<br />basin area co,'ered by each type was estimated so that
<br />weighted ",'erage ratings could be obtained for the
<br />factors shown in table 1.
<br />One or two pace-point transects (Emns and LOI'e,
<br />j95i) were nm in each type to measure bare soil and
<br />co"er of ,-egetation, mulch, and rock. A notch was cut
<br />in one boot sole at the toe, and whatever appeared in
<br />the notch el-ery second step was recorded on (l. multiple
<br />tally cOllllter. unti! 100 obsermtions were made. In
<br />large areas of a single type, longer transects were used
<br />and obsen'ations were made el-ery fourth or si:tth step.
<br />Obserl'ations of rilling, gullJ'ing", pedestaling; erosion
<br />pn ,'ement, and sediment deposition were made nlong
<br />each transect. Surface soils in each type were examined
<br />for texture and cohesh-eness.
<br />The main channel(s) and some tributaries were e;t.
<br />amined to el'ahtnte (1) channel mOl'phology as related
<br />to flow, 1.2\ channel erosion, (3) headcut activity, and
<br />({) sediment deposition. Slope of bottom lands, inter.
<br />mediate pediment areas, and steep uplands was deter.
<br />mined 'l"ith an Abne~' hand le"el.
<br />To statistically compare the estimated sediment
<br />~'ields with regen'oir sediment yields it was necessarJ'
<br />to obtain II specific "IIIue for the estimate mther than
<br />the range of \'alues shown in table 2. Figure 1 was,
<br />therefore, prepared by plotting the upper \'alues of
<br />the l'ating ranges and those of the corresponding esti.
<br />mated sediment )'ields given in table 2.
<br />
<br />T.tDLE 2.-Ratin9 rangel and corre$ponding utimaltd 8tdimcnt
<br />yield ,:,mgu preuribed fn the Padfic SouthU:t$l Inltr.A.gtnc'J
<br />Comml{te~ ~ethod for tl.:aluating sed,'ment yitld8 using ltrrain
<br />cAaraClul3llcs
<br />
<br />P.ati~
<br />Ull9f1
<br />
<br />Ejfilllaltd U3imtllf
<br />yllldrCll1rU
<br />(dCfI-/tPUl1l1ll)
<br />
<br />> 100_.... - _. _ _..... _ _ _ __ _ _. _... __.... __ >3. 0
<br />?.;..!~O......._..._..______.__..__....... I. (}-3. 0
<br />~50::=:::::~::::.:-~_h..."_--.H_h. o. t1. Q
<br />(}-'5 - ..........___....._.0,.0,.)
<br />. ----.---..---.......-......_._______ <0. Z
<br />
<br />SEOIMENr-'(I(LO RATING
<br />
<br />FIGl'U I.-Graph trom which sediment.yield esti-
<br />mates were obtained after the ll"D.tersheds 'had
<br />been rated by the Pacific Soutbn'est Inter-Agency
<br />CommHtee method.
<br />
<br />STUDY AREAS
<br />
<br />Badger Wash
<br />"ine watersheds were el'aluated in the Badger "'ash
<br />drainage (Lusby and others, 1963) on :.\1ancos Shale
<br />about 25 miles west of Grand JIUlction, Colo. RntingS
<br />were mil de on indi,-idual watersheds of 0.0'2 to 0.*8.
<br />square mile in area. and the entire Badger '''ash study
<br />arell of 6.5 square triiles was also e,'aluated as one
<br />watershed.
<br />The steepest watersheds, which hll"e slopes mnging
<br />from to to 100 percent, are underlain by soft shale. A
<br />loose, erodible silt~'.c1ay loam soil, in which roots pene. .
<br />trate to a depth of -1 to 8 inches, cOI-ers these steepest
<br />watersheds. Other. Badger "'ash watersheds with
<br />slopes of from ~ to 30 percent are underlain primarily
<br />b,' JUl"eredsandstone. Soils 011 these watersheds are .
<br />/i~e s;ndJ'loams, ha,'e "er~'little structure, and contain.
<br />roots to II depth of S to 12 inches. Sill: of the Badger
<br />Wash watersheds included in this stud~' are underlain
<br />by interbedded SlIndstone and shale, resulting in inter-
<br />mediate conditions with respect to the shaly and sand~'
<br />watersheds mentioned aOO,'e. Their slopes ronge from
<br />J to 50 percent, IInd the soils are 10ams, usuall~-
<br />mantled with sandstone fragments.
<br />One marked gl'olllorphic feature of the Badger '\' ash
<br />IYutcl'50heds is their relntil'c luck "f boItol\\ !lInd. The
<br />topogrnl'hy consists of steep. rilled upper slopes, dis-
<br />sected moderatelJ' steep pediment slopes, nnd raw
<br />gullies. The gullies, which usually e:dend to the di.
<br />\'ides, hal'e re]ntil'el~. steep gradients and pro\'ide
<br />efficient transport of sediment from the eroding slopes
<br />to the reserl-oirs. These features e:tist because the
<br />
<br />.-
<br />
|