Search

There is a design-to-function knowledge gap regarding how engineered stream restoration structures can maximize hyporheic contaminant attenuation. Surface and subsurface structures have each been studied in isolation as techniques to restore hyporheic exchange, but surface-subsurface structures have not been investigated or optimized in an integrated manner. Here, we used a numerical model to systematically evaluate key design variables for combined surface (i.e., weir height and length) and subsurface (i.e., upstream and downstream baffle plate spacing) structures. We also compared performance metrics that place differing emphasis on hyporheic flux versus transit times. We found that surface structures tended to create higher flux, shorter transit time flowpaths, whereas subsurface structures promoted moderate-flux, longer transit time flowpaths. Optimal combined surface-subsurface structures could increase fluxes and transit times simultaneously, thus providing conditions for contaminant attenuation that were many times more effective than surface or subsurface structures alone. All performance metrics were improved by the presence of an upstream plate and the absence of a downstream plate. Increasing the weir length tended to improve all metrics, whereas the optimal weir height varied based on metrics. These findings may improve stream restoration by better aligning specific restoration goals with appropriate performance metrics and hyporheic structure designs.

Rivers are important ecosystems under continuous anthropogenic stresses. The hyporheic zone is a ubiquitous, reactive interface between the main channel and its surrounding sediments along the river network. We elaborate on the main physical, biological, and biogeochemical drivers and processes within the hyporheic zone that have been studied by multiple scientific disciplines for almost half a century. These previous efforts have shown that the hyporheic zone is a modulator for most metabolic stream processes and serves as a refuge and habitat for a diverse range of aquatic organisms. It also exerts a major control on river water quality by increasing the contact time with reactive environments, which in turn results in retention and transformation of nutrients, trace organic compounds, fine suspended particles, and microplastics, among others. The paper showcases the critical importance of hyporheic zones, both from a scientific and an applied perspective, and their role in ecosystem services to answer the question of the manuscript title. It identifies major research gaps in our understanding of hyporheic processes. In conclusion, we highlight the potential of hyporheic restoration to efficiently manage and reactivate ecosystem functions and services in river corridors.

In this reply we thank both authors for their thoughtful insights on our original opinion piece "Guiding principles for hydrologists conducting interdisciplinary research and fieldwork with participants." We believe these discussions will help to inspire and guide current and future researchers and illustrate how to continue to bring together physical and social data, experiences, and perspectives, and bridge the gap between the two disciplines with respect to socio-hydrological topics. Furthermore, we are confident that these insights and experiences will help foster a deeper understanding for hydrologists and natural scientists engaging with these discussions and research. Here we focus on two important themes that cut across both Quandt and Haeffner's replies: (1) further discussions on the importance of perceptions and lived experiences; and (2) further discussions on collaborative working and some of the major external barriers.

In this reply to Thaler, we take the opportunity to explore two main aspects of his piece to continue the discussion: (1) the integration of data from the social and natural sciences, and (2) the importance of transdisciplinary research. We agree, and highlight that necessary learning, reflections and participation processes are time-intensive for researchers, practitioners and participants. We believe that these discussion pieces are important for informing, engaging, and debating challenges and practices, providing continued opportunities to learn from one another, enabling new forms of research and collaborations to flourish.

To explore and address complex water-related issues, true collaborative, interdisciplinary research at the interface of hydrology and social science is necessary. Accordingly, hydrologists are increasingly working with social sciences and becoming involved in fieldwork with participants. With the overarching aim of facilitating collaboration and interdisciplinary water research, here we discuss important considerations and guiding principles for hydrologists, both those new to and those already familiar with interdisciplinary research, who are: (i) involved in fieldwork with participants; and (ii) working more collaboratively with social scientists. Drawing on first-hand experiences, this paper combines theory and experience from hydrologists and social scientists from their various interdisciplinary research projects to better understand key ethical, theoretical and practical considerations when working with participants. Complementary to this, we discuss the barriers and opportunities in collaborative interdisciplinary research. Facilitating these practices and understandings for hydrologists is essential to strengthen collaboration and to develop more holistic, successful research.

Groundwater is often relied on to provide secure drinking water, particularly in rural Africa, where other options are limited. The increased incidence of drought and its likely escalation due to climate change raise questions as to how resilient groundwater is to drought, and how the performance of different technologies used to access groundwater compares during drought. Here we report the results of three research studies undertaken in Ethiopia to directly address these questions. We first examine hydrographs from 19 wells, springs and boreholes during the 2015/16 El-Niño drought and the years following. Secondly, we report the results of a survey of groundwater recharge for 50 sampled boreholes from 4 woredas (districts) and, lastly, we examine the response of >5,000 different water points from across Ethiopia from January to April 2016 as the drought evolved. The results from the three studies all give a consistent story: groundwater supplies, particularly those accessing groundwater deeper than 15 metres, are resilient to the short-term effects of drought and become increasingly important as other water sources (e.g., springs) fail. Hand-pumpoperated boreholes were often the most reliable sources during drought periods, although motorized boreholes, if accompanied by active monitoring and maintenance, also proved so. Springs and hand-dug wells were generally, but not universally, severely impacted by drought, with those at higher elevations most affected. Recharge studies using environmental tracers suggested that the mean residence time of groundwater (<100 metres deep) is in the order of several decades across the Ethiopian Highlands. This indicates modern recharge is occurring but is not reliant on very recent rainfall; thus, groundwater is both resilient to drought and renewable when managed appropriately. Additional pressures put on groundwater supplies by the drought were shown to be mitigated by an active and sustained campaign of monitoring and mainten

Poor performance of water supply has been a persistent problem in rural Africa. The UPGro Hidden Crisis project (2015 – 2020) has brought together an interdisciplinary research team to investigate and identify different factors affecting the functionality status of boreholes equipped with hand pumps (HPs). A three-tiered survey approach to define and measure functionality was applied to 600 hand pumped boreholes across Ethiopia, Uganda and Malawi. The results, in agreement with national surveys, show that c.80% of hand pumped boreholes produce some water. However, <50% can deliver HP design yield reliably for more than 11 months of the year and far fewer provide water that meet WHO guidelines on chemical parameters and total thermo-tolerant coliforms (TTC). To determine the major contributing factors to functionality outcomes, detailed hydrogeological and engineering investigations, combined with social, institutional and economic factors, were conducted on a subset of 150 HPBs. Within this second survey a full range of HPB functionality outcomes (e.g. aquifer properties, borehole construction and the condition of HP components) were generated. In all three countries water level, aquifer yield, borehole construction and materials, and pump cylinder placement interact to produce conditions that are sub-optimal for HPs to meet design capacity (pumping head and yield). In many instances, the apparent groundwater age from the shallow HPs was at odds with the measured positive counts of e-coli, suggesting a mixture of different age waters and/or contamination issues related to well construction and completion. Improving our knowledge and understanding of handpump borehole functionality in rural Africa will provide the necessary hydrogeological and social frameworks (e.g. functionality monitoring and asset mapping and assessment) that are necessary in evaluating groundwater as a safe and secure water supply to meet the local demands and regional development pressures with