A COMPARISON OF WATER LEVEL DATA OBTAINED BY GLOBAL POSITIONING SYSTEM SURVEYS VS. TOPOGRAPHIC MAP OBSERVATION

Accurate bench marks and water levels, which are important for determining groundwater flow direction, can be established by methods such as Global Positioning System (GPS) surveys or observation of topographic maps. GPS surveys can provide centimeter-level accuracy for hydraulic head spatial coordinates (x, y, and z coordinates), describing the overall hydraulic gradient of the groundwater level within a study area. However, data collection obtained by GPS surveys and processing can be time consuming and unnecessary dependant on the projects requirements. A more time-efficient technique for determining head elevations is the use of topographic and potentiometric surface maps; which yield comparable results with an accuracy and error determined by the scope of a project. The results of a densely spaced (158 positions in 15 x 15 mi area) GPS surface elevation survey conducted within the alluvial aquifer east of the city of Pine Bluff, Arkansas confirms this concept. Water elevations derived from the GPS survey were compared to those determined by the utilization of United States Geological Survey (USGS) potentiometric surface maps of the alluvial aquifer and 7.5 minute topographic map quadrangles. Groundwater flow maps constructed by each method produced accurate and acceptable groundwater elevations and groundwater flow direction. A direct comparison of the flow maps shows minimal differences. While GPS surveys are valuable for obtaining precise measurements, it is often an expended effort for the basic hydrogeologic field investigation.