Catchment-scale recharge and water balance estimates are commonly made for the purposes of water resource management. Few catchments have had these estimates ground-truthed. One confounding aspect is that runoff and soil-water inputs commonly occur throughout the year; however, in climates with strong dry seasons, base flow can be directly sampled. In an experimental catchment in the Mt. Lofty Ranges of South Australia, run-of-stream hydrochemical parameters were monitored. In this Mediterranean climate during the Millennium Drought (2001–2009), the stream was reduced to disconnected groundwater-fed pools. Two groundwater types were identified: (1) high-salinity type from meta-shale bedrock with thick, clayey regolith and (2) low-salinity type from meta-sandstone bedrock with sandy regolith. End-member mixing using silica and chloride concentrations and robust ⁸⁷Sr/⁸⁶Sr ratios reveal an apparent groundwater-flow paradox as follows. According to chloride mass balance and spatial distribution of hydrogeological units, the low-salinity groundwater type has seven times more recharge than the high-salinity type. Over the 28-year record, low-salinity groundwater contributed 25% of stream water, whereas high-salinity groundwater contributed 2–5%. During the drought year, however, annual stream flow from the high-salinity groundwater contributed 50%, whereas low-salinity groundwater contributed 18%. High-salinity groundwater dominated dry-season base flow during all years. The paradox can be resolved as follows: The meta-sandstone terrane drains quickly following wet-season recharge and therefore contributes little to dry-season base flow. Conversely, the meta-shale terrane drains slowly and therefore provides stream flow during dry seasons and drought years.

集水规模补给和水平衡估算通常是为了水资源管理的目的而进行的。几乎没有集水区对这些估计值进行了证实。一个令人困惑的方面是，全年通常会发生径流和土壤水的输入。但是，在干燥季节旺盛的气候中，可以直接采样基本流量。在山的一个实验集水区。在南澳大利亚的崇高范围内，监测了上游的水化学参数。在千年干旱（2001-2009年）的这种地中海气候中，河流被减少到不连接地下水的水池中。确定了两种地下水类型：（1）来自具有厚质粘土重生砾岩的间页岩基岩的高盐度类型，和（2）来自具有砂质重生砾岩的间层砂岩基岩的低盐度类型。⁸⁷ Sr / ⁸⁶Sr比率显示出明显的地下水流悖论，如下所示。根据氯化物的质量平衡和水文地质单位的空间分布，低盐度地下水类型的补给量是高盐度类型的七倍。在28年的记录中，低盐度地下水贡献了溪流水的25％，而高盐度地下水贡献了2％至5％。然而，在干旱年份，高盐度地下水的年流量贡献了50％，而低盐度地下水的年流量贡献了18％。在所有年份中，高盐度地下水占旱季基本流量的主要部分。可以解决以下矛盾问题：湿季补给后，超砂岩地层迅速流失，因此对干季基流的贡献很小。反过来，