Laserfiche WebLink
14 <br />However, hydrographs of four observation wells within the urban area appear to be <br />consistent with well hydrographs representing Dawson, Buffalo, Hall, and Merrick <br />Counties.' <br />Based on this rather meager data sample, urbanization does not seem to be a major factor <br />at a regional level, but may have some local effects. <br />DITCHES AND DRAINS <br />Surface water drainage ditches (e.g., roadside ditches) usually contribute locally to the <br />ground water as they convey surface runoff though areas of deeper ground water. <br />Subsurface drains tend to reduce ground water levels by lowering the discharge elevation <br />point. The extent of ditches and drains has not changed significantly in recent years. <br />LOCAL RIVER AND STREAM LEVELS <br />Rivers act as drains for both surface and ground water. The water level in a local river is, <br />in effect, the spillway elevation for the local ground water reservoir. If the water table is <br />not artificially lowered by pumping, ground water levels will always be higher than a <br />river and ground water will move toward the river. <br />A rise in a river's surface elevation will have some effect <br />on the water table near the river as the ground water <br />adjusts to a higher discharge point. The longer the rise is <br />maintained, the farther from the river the effect will be <br />noticed. However, river rises must persist for several <br />months to have any impact on ground water levels outside <br />of the immediate vicinity of the river, because ground <br />water moves quite slowly through the ground (typically <br />from 10 to 100 feet per year in the sandy Platte Valley <br />soils). <br />The following factors determine the effects that a rise in <br />river level can have on local ground water levels: <br />Because ground water <br />moves slowly, river rises <br />and ground water level <br />rises are not simultaneous <br />if the ground water level is <br />responding to a change in <br />the river. Thus, when <br />ground water levels rise at <br />the same time as the river <br />rises, a third factor (e.g., <br />precipitation) must be <br />involved. <br />' The four well hydrographs observed are 11N- 9W- 4CD -1, 11N- 9W- 12DC -1, 11N -9W- <br />26AA-1, and 11N- 9W- 29BB -1; all of which have records beginning in 1935. <br />Ground Water and River Flow Analyses <br />u <br />j <br />it <br />1 <br />1 <br />C' <br />1 <br />