Alluvial fans often support ephemeral streams whose flow regimes are strongly controlled byfan sedimentary characteristics and interactions with shallow groundwater aquifers. Thehydrogeology of such fans has most often been documented for large fans located within aridclimate regions. This research focuses on a small (0.075 km2) alluvial fan situated in atemperate, high rainfall climate region (the Lake District, North West England). Via anephemeral stream that flows across it, the fan plays a key role in supplying water andsediment to the mainstem River Ehen, which is the focus of a restoration initiativedesigned to conserve populations of the endangered pearl mussel (Margaritiferamargaritifera). The research used Ground Penetrating Radar (GPR) and Electrical ResistivityTomography (ERT), along with high temporal resolution stream flow, groundwater level andstream temperature data, to develop a conceptual model of the fan and its role in controllingthe hydrology of the ephemeral stream. This model is presented here and used to provideinsights into fan and aquifer properties that affect the frequency and magnitude of flowswithin the ephemeral stream and, in turn, delivery of water and sediment to the RiverEhen. Approximately 2.14 km of high resolution (<5m) ERT and 4.11 km of GPR data revealedheterogeneous sedimentary deposits within the fan consisting of debris flow, transitional andsheet flood deposits along with buried palaeochannels and fluvial deposits, all underlain byimpermeable clay till. The upper fan is composed of coarse permeable sediments with high infiltration capacity.Deposits generally become finer and debris flow deposits become increasingly transitionalwith distance from the apex. The conceptual model suggests that buried palaeochannelsprovide preferential groundwater flow pathways. Significant infiltration occurs along much ofthe ephemeral channel, although a less permeable zone occurs around mid-fan. Hydrologicalmonitoring data and observations indicate that the ephemeral stream contributes togroundwater but there appears negligible groundwater contribution to the ephemeral stream. [ABSTRACT FROM AUTHOR]