Abstract
Abstract. Pumping in a vertical well may produce a large drawdown cone near the well. In this paper, the solution is first developed for describing the groundwater flow associated with a point source in a confined aquifer near a stream. Based on the principle of superposition, analytical solutions for horizontal and slanted wells are then developed by integrating the point source solution along the well axis. The solutions can be simplified to quasi-steady solutions by neglecting the exponential terms to describe the late-time drawdown, which can provide useful information in designing horizontal well location and length. The direction of the well axis can be determined from the best SDR subject to the drawdown constraint. It is found that hydraulic conductivity in the direction perpendicular to the stream plays a crucial role in influencing the time required for reaching quasi-steady SDR. In addition, the effects of the well length as well as the distance between the well and stream on the SDR are also examined.
Highlights
Pumping groundwater near a stream can produce a large amount of water which may partially or totally flow from the stream after a certain period of pumping time
A good example is the event happened to the Taoyuan county of Taiwan after the typhoon Matsa occurring on 5 August 2005
The SDR predicted from the point source solution is smaller than that predicted from the solution of the horizontal well perpendicular to the stream when tD is in the range of 100∼600 (t: 0.96∼5.76 min)
Summary
Pumping groundwater near a stream can produce a large amount of water which may partially or totally flow from the stream after a certain period of pumping time. The Shihmen reservoir, located at northern part of Taiwan, is the major source of water supply to the Taoyuan county. The turbidity of the water in Shihmen reservoir reaches 25 000 NTU which exceeds the allowable tur-. Bidity of 50 NTU that the water treatment plant can manage. This resulted in more than 630 000 households without having water supply. The water company drilled wells near the Taoyuan canal for acquiring the low turbid groundwater which came mostly from the canal. As mentioned in Linsley and Franzini (1979), groundwater is usually cleared of sediments if flowing through fine-grained materials within a distance of 30 m
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