Predicting the impact of changing climate and anthropogenic influences on stream discharge dynamics and baseflow conditions requires insight into the main factors that regulate storage and transfer of water from hillslope aquifers to surface streams. Classically, it is assumed that above a certain scale, hydrological laws involved at small-scale can be simplified, allowing the representation of the landscape and its subsurface in models as a homogeneous hillslope with effective slope, length and hydraulic properties. From a comprehensive analysis of hydrological, geological and geomorphological databases available in the Swiss Alps we provide evidence that such simplification might lead to inaccurate estimates of streamflow dynamics at baseflow. We reveal that recession behavior strongly deviates from that predicted by idealized homogeneous theories. A correlation analysis allows us to identify which key features of the landscape might control this deviation, with particular attention to slope, drainage density, depth to bedrock, and lithology as the main drivers. We summarize the current knowledge of physical mechanisms that could lead to complex hydrological behavior in Alpine contexts, and we finally discuss implications in defining modeling strategies for the Critical Zone community.

Despite significant investments in watershed-scale restoration projects, evaluation and documentation of their impacts is often limited by inadequate experimental design. This project aimed to strengthen study designs by quantifying and elucidating sources of error in paired-watershed experiments and evaluating the statistical tools that detect and quantify population-level changes from watershed-scale restoration. Meta-analysis of 32 BACI experiments revealed that synchrony between paired-populations was both weak ( ρ ̵̅ = 0.18) and unrelated to the primary experimental error (r = 0.01), the degree to which paired-populations vary independently in time ( independent variance). Instead, it was found that the sum of the paired-population temporal variances ( total variance), accounted for 91% of the variability that controls statistical power. These findings demonstrate that 1) synchrony in paired-populations does not influence the primary error in BACI field experiments and 2) the magnitude of temporal fluctuations is primarily responsible for this error. The second study component, hypothetical BACI simulations, mathematically relates spatial, temporal and sampling errors to the independent variance and power. Design guidance based on these findings are provided to ensure that future restoration experiments have maximum probability of detecting a present restoration impact. We recommend planners quantify error sources directly from pilot studies and apply the tools provided by this research to estimate statistical power in their monitoring designs. Lastly, we propose a paired-reach design which provides a powerful platform to conduct replicated local-scale restoration experiments, which can build understanding of restoration-ecological mechanisms.

Steam sediment transport is a convolution of climate, weather, geology, topography, biology, and human influence. In addition to providing water and food security for dryland rural communities, sand dams—small weirs designed to trap only the coarse fractions of transported sediments in seasonal and ephemeral streams—illuminate many complexities of geomorphological dynamics. Sand dams store water in interstitial riverbed pores and the size of deposited sediment particles largely determines the recoverability of stored water: fine materials limit transmission and provide lower volumetric yield. Can a sand dam be designed for a particular reach-scale, hydro-sedimentary context to limit capture of fine particles? We argue that the Rouse number provides a useful criterion for identifying regimes where the target material grades are trapped. These ideas were tested using sediment data collected in Kenya and HEC-RAS numerical simulations to evaluate the sensitivity of sedimentation processes to spillway height. We show that constructing sand dams in stages results in more targeted trapping of coarse material. Surprisingly, sedimentation is shown to be more sensitive to variation in spillway height than the flood hydrograph, especially when a dam is short. A method for evaluating the need for spillway staging (essentially controlling the bedform) based on the modeled Rouse number allows evaluation of costs and expected benefits. Beyond sand dams, this supports the observation that for dryland streams with peaky flows and high sediment loading, local hydraulic controls are typically more diagnostic of streambed sediment composition than is the sediment source.