Labels:text | diagram | parallel | line | black and white | document OCR: Determining the Direction Ground Water Flows Ground water usually flows toward, and eventually drains into, streams, rivers, and lakes. The flow of ground water in aquifers does not always mirror the flow of water on the surface. The following steps show how to determine the direction ground water is flowing and the hydraulic gradient within an unconfined aquifer: Surface Step 1. Determine the water Elevation: 725 ft. Surface Elevation: 723 ft table elevation at three locations. Surface T To do this subtract the depth to elevation: 720 ft. Depthto water from the surface elevation Depth to water = 9 ft. at each well. Can you find the woter = 17 ft. water table elevation for each of Depth to the three wells shown in figure 1? woter = 30 ft. Woter Table water table water table elevation water table elevation Figure 1. elevation Well 2 Well 1 Well 3 Step 2. The well locations from step one are shown in figure 2. The difference in water table elevations between each of the wells is determined by subtracting the water table elevation of a well with a higher elevation from the water table elevation of a well with a lower elevation on each of the straight lines connect- ing the wells. These elevation differences are divided up into equal increments as shown in figure 2. Water table elevation levels have been placed on the figure by adding the initial water level to Well #2 each increment. Draw straight 710 lines connecting the increments which have the same values. Figure 2. 710 Well These lines represent the water MO #3 table contours. Direction of ground water Flow feet (Les #1 602 694 696 698 700 702 704 706 O 692 694 696 698 700 702 704 706 708 710 712 50 100 Step 3. The ground water will flow from higher elevations to lower elevations in the direction of maxi- mum change in elevation. The line perpendicular to the straight lines which connect the elevation increments indicates the direction that ground water flows. The vertical change in ground water elevation over horizontal distance, in the direction of ground water flow, is called the hydraulic gradient. It can be determined for this example using the following equation: Water Table Elevation Change Hydraulic Gradient = (in the direction of flow) Horizontal Distance between measurement points This means the water table elevation decreases by feet for every foot the ground water flows.
