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A COMPARISON OF SEVERAL APPROACHES TO MONITOR WATER-TABLE FLUCTUATIONS

Dep. of Natural Resources Science, Univ. of Rhode Island, Kingston, RI 02881

View larger version (14K): [in a new window]   Fig. 1. Device for recording maximum water-table level between site visits. The maximum water-table recording device (MWTRD) is placed inside a 3.2-cm i.d. slotted polyvinyl chloride (PVC) well with a hole in the cap. As the water table rises in the well, the float pushes the magnet up the metal rod. When the water table and the float decline the magnet remains in place recording the highest level the water table reached.

View larger version (24K): [in a new window]   Fig. 2. Water-table fluctuations from 6 Apr. to 13 June 2002 in a coarse loamy Aquic Dystrudept. The solid line represents water-table fluctuations based on data measured with a logger at half hour intervals. The dashed line represents water-table fluctuations based on manual monitoring on a weekly basis. The black triangles represent the highest level the water table reached during the weekly interval as recorded by the magnet on the maximum water table recording device. The "T" under the last water-table inflection indicates the spike used to construct Fig. 3 and 4. The "S" between the vertical dotted lines shows the section of logger data used to calculate the deep seepage rate (0.1 cm h–1).

View larger version (23K): [in a new window]   Fig. 3. Estimated water-table fluctuations 6 Apr. to 13 June 2002 based on weekly measurements adjusted with the use of the water-table recording device. Dashed line represents water-table data recorded weekly. Solid line shows the single-spike method hydrograph; where a single spike, inferred from the position of the magnet on the maximum water-table recording device (MWTRD) as an increase in the water-table level due to a precipitation event, is added to the weekly data. The height of the spike is determined using the magnet data, while the shape is that of the template spike.

View larger version (27K): [in a new window]   Fig. 4. Hydrographs depicting water-table fluctuations from 6 Apr. to 13 June 2002 in a coarse loamy Aquic Dystrudept. The thin line is the hydrograph produced using the logger data. The heavy line is the hydrograph constructed using the precipitation–deep seepage approach where weekly water-table readings are used in conjunction with the magnet data, the spike and deep seepage templates, and daily precipitation data.