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METHODS <br />Site History <br />People knowledgeable about past land use,. river position,. <br />-and vegetation changes were interviewed where possible. We also <br />collected and interpreted aerial photographs of-each site from as <br />-many dates in the past as possible. Our goal of the historical <br />investigations were to determine what the site may have been like <br />- prior to any human modifications of land, groundwater or river- <br />hydrologic.regime,-and how changes have occurred on site. <br />Surface. Water Hydrology <br />One-staff gauge (TNC7)-was. established on the Colorado <br />River. This. gauge became our key to developing stage discharge.., <br />_ relationships between the study area and the Colorado River.. A <br />-total of four staffs had to be placed and surveyed because the <br />river had a seasonal change of approximately 3 meters. An <br />additional 11 staff gauges were installed in ponds throughout the <br />:study area and were monitored regularly. <br />Ground Water Hydrology <br />Depth to ground water was monitored regularly in 10 ground <br />-water monitoring wells. Each-well .was-hand augered in May or <br />early June of 1993 and cased with~3.feet of slotted 1" PVC-.pipe <br />and sufficient unslotted PVC pipe to reach the soil surface. <br />Water levels were measured using an ohm meter well reader.... We11 <br />cosings were surveyed. far latitude, longitude and. elevation <br />during August. 1993 by the U.S. Bureau of Reclamation. <br />Hydrographs for each station are developed by plotting .depth to <br />water level, and or water elevation vs. date. <br />Correlation matrices were developed to .determine which staff <br />:gauges and wells had similar.-trends during the season. In <br />addition, hydrographs were visually compared to segregate them. <br />into groups. -This was done to identify different-water sources, <br />and to determine which stations were connected hydrologically to <br />the Colorado River. <br />Water Chemistry -Water Ouality <br />Surface. and ground water samples were collected for-field <br />- and laboratory chemical analysis. This information is-used for- <br />two purposes: (1) to determine which waters are similar to each <br />.other for the purpose of identifying different water sources <br />affecting the-study area; (2) to determine if any elements or <br />compounds occur in concentrations that could be oxic to fishes. <br />'4 <br />