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" 001541 Director, Colorado Water Conservation Board February 26, 1981 Page 4 stream classes. Second, the stream classification itself, which was based largely upon stream width, was inadequate from the perspective of the needs of the State, i.e., the determination of minimum stream flows. The problem is essentially that minimum stream flows, which are deter- mined by not only stream width but also stream depth, stream gradient, stream bed configuration, and stream bed roughness (variables which are seldom measured in stream inventory studies), are not highly correlated with stream width. The first of these difficulties is real, but not serious, at least when compared with the greater uncertainty present in other parts of the em- pirical data base employed by COWRISM. Better data would be desirable, but the present hydrologic data base is probably adequate for policy- level analyses which require only enough precision to choose between broad and usually quite different options. The second difficulty is more apparent than real. The purpose of COWRISM is to identify those streamflow levels which would be preferred by re- creationists and to predict how recreationists' behavior might be influ- enced by changes in streamflow levels. This is not the same thing as establishing minimum streamflow levels although it is obviously informa- tion which might be used in that activity. If so, it would be used in conjunction with, not as a substitute for, the presently employed Manning's N equation. Actually, it is not clear how Manning's N equation is now used to estab- lish minimum streamflows, because the equation has no normative content. It simply predicts what the rate of streamflow (cfs) will be under sti- pulated stream characteristics (width, depth, gradient, roughness of bed) as a function of the amount of water contained in the stream bed at any given time and place. Doubtless, the Division of Wildlife field per- sonnel do use this equation in establishing minimum streamflows, but they must couple it with unspecified value judgments in order to produce a recommendation. The equation itself will not do so. The value judg- ments are probably associated with technical considerations related to fishery productivity and maintenance, and must also include, whether ex- plicitly or implicitly, value judgments concerning desirable levels of fish populations. COWRISM simply obtains parallel, and possibly dif- ferent, value judgment data from the recreationists themselves rather than from the biologists. Obviously, biologists know some things which recreationists don't know (how fish populations relate to streamflows) and recreationists know some things which biologists don't know (what recreationists want). A reasonable procedure for establishing minimum