Proglacial fields typically have complex topography and heterogeneous sediments, resulting in highly variable flow and temperature regimes in surface runoff and groundwater. Using data from the Damma glacier forefield (Switzerland), we examined how longitudinal stream temperature changes can be used to infer reach-averaged hydrological and thermal processes in proglacial riparian zones. A simple energy balance showed that (1) radiative forcing and frictional warming largely explained the observed temperature patterns in three stream reaches, and that (2) groundwater inflow and/or hyporheic exchange appear to influence stream warming along a fourth reach. Daytime stream warming depends on channel width, and here we show that stream temperature measurements can be used to infer reach-averaged hydraulic geometry relationships between stream width and discharge, which are normally difficult to obtain by other methods in braided gravel bed streams. Our results illustrate how proglacial stream temperatures can yield spatially integrated information about hydrological and thermal processes in glacial forefields, where extreme spatial heterogeneity makes conventional methods difficult to apply.