Comment on “Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties” by X. Chen and X. Chen

Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] carried out a study that is very similar to that of Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734]. Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] made the analysis for a few specific cases with very similar hydraulic properties, while that of Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734] presents results in dimensionless form that can be used for a wide range of hydraulic parameter values, pumping rates, pumping durations, and error magnitudes. In one case Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] made a mistake in their analysis. In other cases inaccuracies in the approximations used by Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] seem to have lead to results that they misinterpret. Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] would have been concerned about this if they had studied and compared with the results of Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734] that were published more than 2 years before their submittal. This would also have shown that the major conclusions of Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] were already made by Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734], that the results and conclusions of Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734] have more general applicability than those of Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284], and that Christensen [Christensen, S., 2000. On the estimation of stream flow depletion parameters by drawdown analysis. Ground Water 38 (5), 726-734] carried the study further and shows how parameter uncertainties propagate into uncertainty of stream flow predictions. Chen and Chen [Chen, X., Chen, X., 2003. Sensitivity analysis and determination of streambed leakance and aquifer hydraulic properties. Journal of Hydrology 284, 270-284] applied the technique to a field case study. Similar applications were published by Nyholm et al. [Nyholm, T., Christensen, S., Rasmussen, K.R., 2002. Flow depletion in a small stream caused by ground water abstraction from wells. Ground Water 40 (4), 425-437] and by Kollet and Zlotnik [Kollet, S.J., Zlotnik, V.A., 2003. Stream depletion predictions using pumping test data from a heterogeneous stream-aquifer system (a case study from the Great Plains, USA). Journal of Hydrology 281, 96-114].