A Comparison of Tools and Methods for Estimating Groundwater-Surface Water Exchange

A comparison of tools for measuring discharge rates in a sandy streambed was conducted along a transect near the north bank of the Grindsted Å (stream), Denmark. Four tools were evaluated at six locations spaced 3 m apart in the stream: mini-piezometers, streambed point velocity probes (SBPVPs), temperature profilers, and seepage meters. Comparison of the methods showed that all identified a similar trend of low to high groundwater discharges moving westward along the transect. Furthermore, it was found that the differences between discharges estimated from Darcy calculations (using the mini-pizometers), and SBPVPs were not statistically different from zero, at the 90% confidence level. Seepage meter estimates were consistently lower than those of the other two methods, but compared more reasonably with the application of a correction factor of 1.7, taken from the literature. In contrast, discharges estimated from temperature profiling (to a depth of 40 cm) were found to be about an order of magnitude less than those determined with the other methods, possibly due to interferences from horizontal hyporheic flow. Where the various methods produced statistically different discharge estimations at the same location, it is hypothesized that the differences arose from method-specific sources of bias, including installation depths. On the basis of this work, practitioners interested in measuring flow across the groundwater-surface water interface achieve the least variability with seepage meters and the SBPVP. However the accuracy of the seepage meter depended on a calibrated correction factor while that of the SBPVP did not.     

Comparison of Two Computational Methods for Estimating Transmissivity Based on the Picking Equation

A comparison is presented of two computational methods, PICKINGmodel and PPC-Recovery, to estimate transmissivities based on the Picking equation using water-level recovery data from brief pumping tests of relatively low-yielding domestic wells. The tests were performed by the United States Geological Survey (USGS) in 50 domestic bedrock wells in south-central New York State, and USGS staff performed the analysis using PICKINGmodel based on the Picking equation. The results indicated that the estimated transmissivities ranged from 0.86 to 2900 ft²/d (0.080 to 270 m²/d) with a median of 41 ft²/d (3.8 m²/d). The same data were later analyzed using PPC-Recovery also based on the Picking equation. The two sets of estimated transmissivities were compared and statistically had the same median value at a probability of 95%. In another analysis, the PPC-Recovery method was applied to the same data that had been truncated at the point when the slope of the recovery data curve began to deviate from a straight line aligned with the middle portion of the recovery data. Comparing these resulting estimates of transmissivity with values originally obtained using the PICKINGmodel, the two had statistically the same median value for transmissivity at a probability of 95%. It was concluded that using PPC-Recovery in this manner to estimate transmissivity in low-yielding domestic wells will yield transmissivity values sufficiently close to the results had PICKINGmodel been used, and with less time and effort.     

利用广东数字地震波资料对比分析计算环境剪应力场的方法

根据陈培善推导的多个环境剪应力场公式,利用广东数字地震台网记录到的华南地区60个ML≥2.5地震参数分别对0τ进行计算。相对偏差及相关性分析表明,由震源峰值加速度ap计算的0τ5相对偏差最小,与其他方法的相关性最高。对于数字化地震资料,ap的求解较为简便,由此计算环境剪应力场的方法更适合在日常分析预测工作中推广应用。