Headwater catchments provide substantial streamflow to rivers even during long periods of drought. Documenting the mean transit times (MTT) of stream water in headwater catchments and therefore the retention capacities of these catchments is crucial for water management. This study uses time series of ³H activities in combination with major ion concentrations, stable isotope ratios and radon activities (²²²Rn) in the Lyrebird Creek catchment in Victoria, Australia to provide a unique insight into the mean transit time distributions and flow systems of this small temperate headwater catchment. At all streamflows, the stream has ³H activities (<$<$2.4 TU) that are significantly below those of rainfall (∼$\sim$ 3.2 TU), implying that most of the water in the stream is derived from stores with long transit times. If the water in the catchment can be represented by a single store with a continuum of ages, mean transit times of the stream water range from ∼$\sim$6 up to 40 years, which indicates the large retention potential for this catchment. Alternatively, variations of ³H activities, stable isotopes and major ions can be explained by mixing between of young recent recharge and older water stored in the catchment. While surface runoff is negligible, the variation in stable isotope ratios, major ion concentrations and radon activities during most of the year is minimal (±$\pm$ 12%) and only occurs during major storm events. This suggests that different subsurface water stores are activated during the storm events and that these cease to provide water to the stream within a few days or weeks after storm events. The stores comprise micro and macropore flow in the soils and saprolite as well as the boundary between the saprolite and the fractured bed rock. Hydrograph separations from three major storm events using Tritium, electrical conductivity and selected major ions as well a δ¹⁸${\delta }^{18}$O suggest a minimum of 50% baseflow at most flow conditions.

We demonstrate that headwater catchments can have a significant storage capacity and that the relationship between long-water stores and fast storm event subsurface flow is complex. The study also illustrates that using ³H to determine mean transit times is probably only valid for baseflow conditions where the catchment can be represented as a single store.

The results of this study reinforce the need to protect headwater catchments from contamination and extreme land use changes.

即使在长期干旱期间，源头集水区也为河流提供了大量的水流。记录源头流域中溪流水的平均运输时间（MTT），因此记录这些流域的保留能力对于水管理至关重要。这项研究结合澳大利亚维多利亚州Lyrebird Creek流域的³ H活度时间序列，主要离子浓度，稳定的同位素比和ra活度（²²² Rn），提供了对澳大利亚平均传播时间分布和流动系统的独特见解。这个温带的小水源流域。在所有流中，流都具有^3个H活动（<$<$2.4 TU）明显低于降雨量（〜$〜$3.2 TU），这意味着溪流中的大部分水来自运输时间较长的商店。如果集水区中的水可以由一个具有连续年龄的单一商店来代表，则溪流水的平均通过时间为〜$〜$长达40年的6年，这表明该流域具有很大的保留潜力。另外，³ H活度，稳定同位素和主要离子的变化可以通过新近注入的新水和流域中存储的较老水之间的混合来解释。尽管表面径流可以忽略不计，但一年中大部分时间里稳定同位素比，主要离子浓度和ra活度的变化很小（±$\pm$12％），并且仅在重大风暴事件期间发生。这表明在暴风雨事件期间激活了不同的地下蓄水设施，并且在暴风雨事件发生后的几天或几周内这些蓄水设施不再向溪流提供水。储层包括土壤和腐泥土中微孔和大孔的流动，以及腐泥土和裂隙基岩之间的边界。使用氚，导电性和选定的主要离子以及一个从三大风暴事件过程线分离δ ¹⁸${\delta }^{\mathrm{18岁}}$O建议在大多数流动条件下至少有50％的基流。

我们证明了源头集水区可以具有很大的存储能力，并且长期蓄水量与快速风暴事件地下流量之间的关系很复杂。该研究还表明，使用³ H来确定平均渡越时间可能仅对将集水区表示为单个商店的基流条件有效。

这项研究的结果加强了保护源头集水区免受污染和极端土地利用变化的需求。