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OJJ192 21 -During high discharges downstream of Pueblo, the critical velocity technique can often be used to estimate velocity when sandboils and stand- i ng waves a re noted i nthe stream channe I I nd i cat i ng a ve I oei ty of f I ow of a Froude number of about 1.0. Here the instahility of critical flow is ap- parent with the standing waves, which is further evlcenced by the associated sandboils -- a manifestation of the river attempting to readjust its depth to keep its velocity subcritical. CHANGE IN STAGE Transit loss and travel times are related to the change in stage of the river. The most commonly used hydraulic formula for river flow is Manning's equation Q A ~ R2/3 SI/2 n whe re Q is the flow in cfs A is the area in square feet n is the Manning roughness coefficient R Is the hydraulic radius, and S is the slope of the hydraulic gradient In feet per foot. The hydraulic radius and the area both have significant effects upon the dis- charge, and both are directly related to the stage. Relatively large Increases In the discharge can result with rather minimal changes In the stage, and it is for this reason that it is not always readily apparent where the transported water is at any given time. The change in st~e is usually related to the change In surface area of the river, which in turn affects the evaporation rate from the river. Studies indicate that between Granite and Nepesta the average stage increase between 200 and 400 cfs is .50 feet where the average increase In stage between 800 and 1,000 cfs is .25 feet. As the discharges rise, the change In stage di- minishes for equal increments of flow. The average total rise in the river from 100 cfs to 1,000 cfs is approximately two feet. CHANNEL CROSS SECTIONS The Arkansas River above Canon City is generally a degrading stream and Is generally well Incised in its valley. Even in reaches where there is an evident flood plain, the channel has Incised itself there and is represented by a channel having steep banks. East of Canon City, where the slopes are much more mild and where wide flood plains exist, the normal flow channel is well defined, with the banks ranging in steepness from nearly straight up and down to 1:1 or 2:1 slopes. The average width of the river above Canon City during a mean summer flow ranges from 80 to 120 feet. Below Canon City the range is between 140 and 210 feet. The steep banks which generally exist along the study reach mean that ordinary increases in river stage do not greatly increase the top width, and