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_..__ <br />-- <br />The presence of South Platte River adds another special type of boundary to the- - - - <br />model that must be cazefully set-up to achieve a:valid simulation. In the case of - ..... _ <br />typical creeks-and rivers in the grid-west, it is common practice to include the live .. <br />channel as well as the main stream alluvial channel of the creek as part of the . <br />overall stream system.. The interconnection of that set of stream cells with the. -~.. <br />underlying aquifer is simulated through a representation of the bottom of the <br />alluvial channel that allows flow of water to and from the underlying .aquifer _ - <br />- :: depending .on- he relative- head of xhe live flow: and the ambient, head in.. the- <br />aquifer at that particular cell. <br />The model requires for each stream cell input, a value for the pazameter known as <br />stream conductance. This conductance factor is a composite number made up of <br />the surface azea of the stream-alluvium as it traverses the cell, the relative vertical <br />hydraulic conductivity of the bottom of the stream channel, and the thickness of <br />any less conductive layer that may be present at the base of the alluvial channel. <br />In the subject model; the length of the stream channel in each cell was measured <br />from topographic maps, the width was set at 75-feet throughout, and the leakage <br />factor (the ratio of the vertical hydraulic conductivity and the thickness of the <br />lower conductivity layer, or "k/m" ratio) was derived from published values <br />utilized by the State Engineer's Office. These factors were combined for each cell <br />to generate the conductance values used. The conductance values are thus <br />combined factors that can ailow for quick relative adjustment through the use of <br />multipliers. This is important in that it is very difficult to derive empirical data on <br />7 <br />Martin and Wood Water Consultants, Inc. <br />