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HYDRAULIC GEOMETRY <br />Understanding the effects of flow in a river <br />requires information about the river's <br />hydraulic geometry. Hydrology describes how <br />much water is available and its discharge over <br />a period of time. Hydraulics, in contrast, <br />characterize the important components of <br />flowing water: depth, velocity, size of waves, <br />the proportion of a stream channel and <br />floodplain that is inundated, the quantity of <br />sediment a particular flow is capable of <br />transporting, etc. Hydraulics are obviously <br />critical when looking at the direct effects of <br />flow, but they play an important role in <br />exploring indirect effects as well. <br />When specific hydraulic variables are <br />expressed as a function of flow, "hydraulic <br />geometry" relationships can be developed. <br />As in the example given in the sidebar on page <br />21, these relationships can help researchers <br />decide which flows will provide adequate <br />boating depths or which will inundate <br />camping beaches. Hydraulic geometry <br />calculations are also the starting point for <br />exploring potential changes in geomorphology <br />or riparian vegetation. For example, <br />researchers exploring how different flows <br />affect the size of beaches must begin by <br />understanding the depths, velocities, and <br />sediment - carrying capabilities of various flows <br />in a beach area. One of the critical tasks in this <br />case would be to develop hydraulic <br />relationships at a transect site representative of <br />beach areas. <br />determine which flow would provide a depth suitable for boat passage. <br />g1] <br />