Multi-temporal image analysis of very-high-resolution historical aerial and recent satellite imagery of the Ahnewetut Wetlands in Kobuk Valley National Park, Alaska, revealed the nature of thaw lake and polygonal terrain evolution over a 54-year period of record comprising two 27-year intervals . Using active-contouring-based change detection, high-precision orthorectification and co-registration and the normalized difference index, surface area expansion and contraction of 22 shallow water bodies, ranging in size from 0.09 to 179 ha, and the transition of ice-wedge polygons from a low-to a high-centered morphology were quantified. Total surface area decreased by only 0.4% during the first time interval, but decreased by 5.5% during the second time interval. Twelve water bodies (ten lakes and two ponds) were relatively stable with net surface area decreases of ≤10%, including four lakes that gained area during both time intervals, whereas ten water bodies (five lakes and five ponds) had surface area losses in excess of 10%, including two ponds that drained completely. Polygonal terrain remained relatively stable during the first time interval, but transformation of polygons from low-to high-centered was significant during the second time interval.
Existing methods for the determination of horizontal aquifer anisotropy by means of pumping tests require a minimum of four wells, one for water withdrawal and three for drawdown observations. This paper shows how the same methods can be used to determine anisotropy with as few as three wells, if at least two of them can be pumped in sequence. A field example is included. A method of analyzing data from more wells than the above minimum, by least squares, is also described.
A vertical circulation well is a well completed in two intervals with extraction induced in one interval and injection induced in the other, generating a circulating flow field near the well. A vertical circulation well may be used to remediate contaminated ground water by air stripping the extracted water and then reinjecting the clean water; by introducing oxygen and/or nutrients to the extracted water before reinjecting it, thereby stimulating the natural bioremediation of the water; or by injecting appropriate chemicals or microbes, effecting remediation of the circulated water. This paper summarizes an analytical technique for predicting the steady‐state hydraulic head and flow fields caused by the operation of multiple vertical circulation wells in a confined aquifer with a regional gradient. The method begins with the hydraulic head solution for a point sink in an infinite aquifer. The point sink is then integrated to derive the solution for a line sink. Linear superposition is applied to obtain the hydraulic head resulting from multiple line sinks and sources in a homogeneous confined aquifer. This solution is then differentiated to obtain the hydraulic head gradient and three‐dimensional velocity field. The velocity field is numerically integrated by an adaptive Runge‐Kutta scheme to obtain the pathlines of three‐dimensional flow.
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