Predicting groundwater flow behavior in non-uniform aquifers in contact with a stream: an extension to ditch drainage

摘要

One-dimensional unsteady-state groundwater flow in various aquifers (uniform, non-uniform, fractured, semi-infinite, finite), resulting from a step change in the stream stage is reviewed as a stream-aquifer interaction problem. An analytical model developed earlier for finite fractured aquifers is extended to the problem of ditch drainage without replenishment in a fractured formation. The equations describing transient water table variations between drains, the evolution of the midpoint water table elevation with time, and the variation of the drain discharge with time are presented. An approximate formula for drain spacing is proposed. The differences between the behaviour of flow in a uniform homogeneous aquifer and that in a fractured aquifer are discussed. The results of the analysis showed that the ratio of storage coefficients of blocks and fractures, and the block-to-fracture hydraulic conductivity contrast are the influencing parameters. The proposed analytical model may be used for the design of unsteady-state drainage systems in fractured soils, and for dewatering problems where the water table is close to the ground surface, for example, in urban environments where rising groundwater levels are a problem.