A comprehensive exploration of streamflow dynamics at the watershed scale in non-perennial rivers is an arduous task. In the lower Himalayan region, the presence of numerous intermittent and ephemeral streams contributes to high volume of water for small duration and transports significant amount of sediment to downstream. Fluvial alterations reshape stream geomorphology, triggering flash floods. To map those head water streams, a comprehensive study within the lower Himalayan watershed of area 56.61 km2 has been done by developing the low-cost capacitive soil moisture sensors. This real time monitoring sensor is a microcontroller-based system and an indirect method for indicating the soil moisture content. These sensors have been strategically deployed across three distinct sub-watersheds within the headwater watershed to capture the continuous soil moisture response during the monsoon period in 2023. For analyzing this study, on-field data was collected from automated weather stations (AWS) to obtain rainfall data, which was complemented by the utilization of stage-discharge curves for a more thorough understanding of discharge fluctuation. During 2023 monsoon period 9 rainfall events were recorded and identified as small, medium, and high to get the rainfall- runoff relationship with antecedent moisture condition (AMC). From the analysis different signatures in capacitance value are found to be affected by several factors which include slope, % area, stream order and land cover. These thresholds will aid in accurately mapping streams, and by quantifying discharge capacity, sediment transportation analyses can be facilitated in future. This study will enhance management strategies for sediment transport and ecological health within the high-gradient headwater watersheds. 

How to cite: Choudhary, D., Sen, S., and Kulkarni, R.: Development of low-cost soil moisture sensor to capture the response of headwater streams in lower Himalayan region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15164, https://doi.org/10.5194/egusphere-egu24-15164, 2024.

In recent times, several countries all around the world are experiencing groundwater droughts that are drying up surface water bodies (SWBs), such as rivers, marshes, lakes, etc. For implementing proper water management strategies, it is important to identify the SWBs that are continuously dependent upon the local groundwater reserve to feed them. SWBs that have some reserve throughout the year are fed by the local groundwater during the dry seasons. The rivers, lakes, and wetlands that exhibit these characteristics are referred to as perennial SWBs. Losing SWBs refers to the rivers, lakes, and wetlands for which the groundwater table is lower than the surface water elevation, and thus do not possess perennial characteristics. The water spread areas of SWBs in the Godavari basin are mapped by utilizing Normalized Difference Water Index (NDWI) or Automatic Water Extraction Index (AWEI). The NDWI or AWEI were obtained by using multi-temporal Landsat or Sentinel Satellite datasets in the Google Earth Engine (GEE) platform. Due to the limited spatial resolution of the satellite data, this analysis only considers water bodies with a surface area greater than 3,600 m². The standardized water spread area index (SWSAI) is used to calculate the magnitude of the surface water drought of different water bodies with respect to space and time. The SWSAI is determined by using the water spread area from NDWI or AWEI by assuming that the water spread area increases due to increase in water surface elevation.  The standardized groundwater table index (SGWTI) is used here to compute the magnitude of groundwater table drought by using the depth of the water table in different observation wells obtained from various central and state government agencies in India. The primary goal of this study is to identify and map the drought sensitive zones responsible for river aridity by plotting correlation matrix for SGWTI of different observation wells. The second objective of this study is to map the spatio-temporal variation of SWSAI of different surface water bodies like ponds, lakes, and wetlands, etc. in the Godavari River Basin, India. The third aim is to determine the correlation between the SGWTI and SWSAI as well as identify the surface water bodies that are influenced by groundwater drought. By this procedure, it would be feasible to determine whether or not there is a connection between the travel time for the groundwater drought propagating from minor surface water bodies (wetlands, lakes, ponds, etc.) to major ones (rivers). It can thus be proved that the surface water dryness in wetlands, lakes progresses towards the rivers due to presence of groundwater drought in the river basin. A correlation (ranging from 0.81 to 0.9) between the depth of connectivity of surface water-groundwater with the SGWTI is computed in this study to demonstrate that the upper Godavari River is highly affected by the groundwater drought, whereas, the middle Godavari river is moderately influenced and the lower Godavari river is less influenced by it.

How to cite: Prashanth, T., Ganguly, S., Gummadi, M., and Teppala, D.: Identification and mapping the surface water bodies that are sensitive to groundwater drought in the Godavari basin, India , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-55, https://doi.org/10.5194/egusphere-egu24-55, 2024.

At present there is a great lack of hydrological information on non-perennial rivers. In many cases, there is no knowledge of which river reaches are subject to non-flow periods, and the duration of non-flow and dry periods remains unknown. Few hydrometric stations are present along non-perennial rivers, and these stations provide point information, limiting the ability to describe the flow conditions across a river reach. For example, they do not allow to distinguish a continuous line of flow from an isolated pools condition. In contrast, approaches based on field surveys or citizen science can provide information on flow condition over entire river reaches but their temporal resolution is generally poor. Within this framework, satellite remote sensing provides significant opportunities due to the possibility of monitoring large areas with high temporal resolution. However, the use of satellite images for monitoring non-perennial river regimes has so far been limited by the availability of images with adequate spatial resolution and their accessibility in terms of cost. Multispectral satellite data freely distributed by the European Space Agency's Copernicus Sentinel-2 mission, with a spatial resolution of 10 m and an acquisition frequency of approximately five days, represent an appropriate trade-off point for monitoring non-perennial rivers with active channels not covered by vegetation and larger than about 40 m.

In this study, we investigated the capability of Sentinel-2 data to differentiate among three flowing states of non-perennial rivers: "flowing" (F), "ponding" (P), and "dry" (D). The analysis was performed for 5 reaches of the streams Sciarapotamo, Mingardo and Lambro (Campania region, Italy). By analyzing the spectral signatures of land cover within river corridor, we identified the bands in which land cover classes are most differentiated. Utilizing these specific bands, we created a false-color image in which the pixels covered by water stand out from the background. The comparison between false color images and field acquired ground truth showed very good agreement. For all the archive data (since 2015) we identified one of the three possible flowing status: F, P and D. The acquired dataset was utilized to train a Random Forest model capable of predicting the daily occurrence of specific flowing statuses (F, P, D), using spatially interpolated rainfall and air temperature data as predictors. The model demonstrated strong performance in terms of accuracy (ranging from 82% to 97%) and true skill statistic (ranging from 0.65 to 0.95). In each of the five years of the observation period, all the reaches underwent no-flow condition for at least a few days and in some cases up to four months. Three of the five reaches were completely dry each year while the other two never dried completely. With its ability to monitor the presence of water in a cost-effective manner, this method has the potential to significantly improve the knowledge on non-perennial rivers regimes.

How to cite: Cavallo, C., Papa, M. N., Negro, G., Gargiulo, M., Ruello, G., and Vezza, P.: Estimating the duration of flow status along non perennial rivers by satellite data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17373, https://doi.org/10.5194/egusphere-egu24-17373, 2024.

How to cite: Durighetto, N. and Botter, G.: The shape of the active length vs streamflow relation in temporary streams, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9748, https://doi.org/10.5194/egusphere-egu24-9748, 2024.

Temporary streams (i.e., non-perennial streams) cover more than half of the global stream network. They are highly dynamic systems and important habitats. Still, they have so far not been thoroughly monitored because gauging stations are expensive, not well suited for measuring zero flows, and provide only data for a single location in the stream network. An alternative way to monitor temporary streams is by visual assessment. However, on-the-ground surveys of stream networks tend to be highly time-consuming. Hence, visual observations by citizen scientists provide a great opportunity to collect high spatial- and temporal resolution data, even though there are challenges regarding the accuracy and irregularity of the observations.

To assess the potential of citizen science data to obtain temporal resolved information on the state of temporary streams, we used the observations submitted by citizen scientists using the CrowdWater app for 63 locations on a 5 km² forested hill in Zurich, Switzerland. The number of observations per location during the last three years varied from 1 to 257 (median: 40). There was at least one stream state observation for 402 days, with a maximum of 42 observations per day and a median of 10 observations per day. In addition, trained staff monitored 59 streams (30 overlap with the citizen science data set) at an almost bi-weekly resolution during six months (24 days of observations at all 59 points).

The hierarchical structure of channel network dynamics postulates the existence of a fixed, unique order according to which stream segments are activated during network expansion (from the most to the least persistent). To understand the hierarchical structure of stream wetting and drying at the study site, we applied the graph-based method developed by Durighetto et al. (2023) on the available data. This data-driven method would allow us to fill the gaps of the irregular citizen science data (leading to 25,728 reconstructed observations compared to the 4,354 original observations). The hierarchical structures for the two datasets differed, even if only locations that were part of both data sets and the same period were used to determine the hierarchical structure. In the citizen science dataset, the order of activation of the observed stream locations is less clearly identifiable (i.e., more uncertain). This is likely due to the non-systematic and sporadic nature of the data, i.e., only a few stream observations on the same date, as well as errors in the data. Nonetheless, this information can be used to give guidance to the citizen scientists on which streams to observe more frequently because they provide the most crucial information about the wetting and drying patterns of the network.

Reference: Durighetto, N., Noto, S., Tauro, F., Grimaldi, S., & Botter, G. (2023). Integrating spatially-and temporally-heterogeneous data on river network dynamics using graph theory. Iscience, 26(8).

How to cite: Scheller, M., Durighetto, N., van Meerveld, I., Seibert, J., and Botter, G.: Combining citizen science data and the hierarchical structuring of temporary streams to reconstruct the patterns of channel wetting and drying, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15302, https://doi.org/10.5194/egusphere-egu24-15302, 2024.

While the role of climate conditions in controlling streamflow intermittence is well recognised, the assessment and modelling of the role of groundwater remains a challenge. In this study, we use process-based 3D groundwater flow models to simulate stream intermittency in groundwater-fed headwaters. Streamflow measurements and stream network maps are considered together to constrain the effective hydraulic properties of the aquifers. The modelling framework has been applied and validated in pilot catchments with unconfined crystalline aquifers (France) with contrasting geomorphological settings. We present the calibration framework, the analysis of uncertainties and discuss the underlying mechanisms governing the different dynamics of streamflow intermittency. The models are then used to predict streamflow intermittence under future climate scenarios. Intuitively, with decreasing recharge rates, systems with lower storage capacities lead to higher water table fluctuations, increasing the proportion of intermittent streams and reducing future perennial flows. However, the pilot sites reveal nuanced feedback mechanisms among future climate variations, groundwater recharge dynamics, and stream intermittence, where the geomorphic characteristics of the landscapes are key to regulating these feedbacks.

How to cite: Abhervé, R., Roques, C., de Dreuzy, J.-R., Datry, T., Brunner, P., Longuevergne, L., and Aquilina, L.: Process-based 3D groundwater flow model to simulate current and future stream intermittence in headwaters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17603, https://doi.org/10.5194/egusphere-egu24-17603, 2024.

Intermittent rivers and ephemeral streams (IRES) are watercourses that stop flowing at some point during the year. IRES are found in all climates and biomes and their occurrence is predicted to increase with climate change and increasing demand for freshwater. Knowledge of biogeochemical cycles in IRES is mainly based on research in the Mediterranean region. The region of Brittany in western France, characterised by a temperate oceanic climate and intensive agriculture, offers research opportunities to understand C-N-P dynamics in temperate IRES with high nutrient loadings.

In this work, we analyse the spatial variability of C-N-P concentrations in the intermittent stream network of the Kervidy-Naizin catchment (7 km²) during the different phases of intermittency. We hypothesise that the spatial variability of C-N-P concentrations increases during the stream fragmentation, as the formation of isolated pools leads to different physico-chemical conditions due to variable solar radiation, temperature, and nutrient availability. To investigate this, we conducted repeated synoptic sampling campaigns at a high spatial resolution (every 100 to 200 m) along the stream network during the spring-summer of 2023. We sampled forty sites and analysed, among others, DOC, DIN and TP and physico-chemical parameters (conductivity, redox potential, temperature and pH) during four field campaigns spanning from stream recession to the rewetting phase after the summer dry period.

The results showed an increasing spatial variability of concentrations with stream fragmentation, with spatial coefficients of variation increasing from 27% to 49% for DOC, from 15% to 64% for DIN and from 44% to 74% for TP. During the stream fragmentation, mean DOC concentrations increased from 2.43 to 4.76 mg.L^-1, mean DIN concentrations decreased from 15.1 to 8.47 mg.L^-1 and mean TP concentrations increased from 0.023 to 0.071 mg.L^-1. Spatial patterns of concentrations observed during the flowing phase tended to be disrupted by the stream fragmentation, with isolated pools exhibiting extremely high or low concentration values. We interpret these changes in spatial patterns as a consequence of redox processes and nutrient assimilation.

How to cite: Casanova, A., Dupas, R., Jaffrezic, A., and Fovet, O.: Spatial variability in C-N-P concentrations during the fragmentation of an intermittent stream in a temperate agricultural catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9917, https://doi.org/10.5194/egusphere-egu24-9917, 2024.

Hydrological studies on temporary streams are crucial for understanding their activation and response during wet and dry conditions. Additionally, the use of geochemical tracers (e.g., electrical conductivity, water stable isotopes, major ions) can help assess the impact of climate change on these ephemeral water bodies. This study aims to i) investigate the relation between discharge and tracer concentration at different spatial scales and at the seasonal and event scales; ii) analyze the effect of antecedent conditions on tracer temporal variability at different spatial scales; iii) compare the contribution of rainwater to stream runoff at three scales during selected rainfall-runoff events. The work relies on an integrated database of isotopic and geochemical compositions of water samples coupled with hydrometeorological data from the Regional Environmental Agency (ARPAV) in the 116 km² Posina catchment in the Italian pre-Alps. The lithology consists mainly of carbonate rocks, and the typical fracturing of dolomites and limestones facilitates water infiltration, thus favoring the presence of temporary streams during dry periods. Conversely, the limited presence of volcanic rocks in some sub-catchments tends to favor perennial streams characterized by a rapid response to rainfall events. In this work, water samples were collected from the Posina river and its main tributaries between September 2015 and March 2019. Temperature and electrical conductivity were measured in the field by portable probes, whereas major ions and water stable isotopes were analyzed by ion chromatography and laser spectroscopy, respectively. Preliminary results show that relationships between discharge and tracer concentration reveal significant associations: δ¹⁸O increases with discharge, whereas electrical conductivity (EC) shows a decreasing trend with discharge, better represented by logarithmic and polynomial functions for different selected sections of the main streams and tributaries. Similar trends are observed for sulphates and sodium.  Discharge data at Ressi (a tributary flowing on volcanic rocks) and Posina at catchment outlet have also been compared with selected tracer data from water samples from these two sections. Positive correlations are found between average tracer concentration (δ²H, δ¹⁸O, and nitrates) and peak antecedent discharge, while negative correlations exist for δ²H, EC, chloride, sulphates, bicarbonate ions, sodium, magnesium, and calcium. Antecedent precipitation positively correlates with δ²H and nitrates but negatively with sulphates and sodium. EC shows positive (negative) correlations with δ²H and nitrates (sulphates and sodium), respectively, with varying patterns along different sections and tributaries. The 5-day antecedent rainfall exhibits the highest correlations with tracer compositions, particularly for EC, δ²H, and nitrates. The obtained results suggest the importance of an interdisciplinary approach in the analysis of the hydrological and geochemical connectivity of temporary stream networks.

How to cite: Marchina, C., William, A., Ylenia, G., Marco, B., and Giulia, Z.: Exploring tracer dynamics at different spatial scales in a pre-Alpine catchment with a temporary stream network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12388, https://doi.org/10.5194/egusphere-egu24-12388, 2024.

This study investigates the spatio-temporal dynamics of water quality in a 70 km² mixed land use, lowland catchment in NE Germany over a four-year period (2018-2022). During this period with a consistent negative rainfall anomaly compared to the long-term average, the intermittent stream network exhibited three distinct hydrological phases each year, with important implications for water quality. Autumn and early winter featured a connecting phase, where spatially variable stream flows responded to rising water tables following increased rainfall and reduced evapotranspiration. The winter and early spring saw a fully connected phase, marked by increased stream flows throughput the catchment. Late spring and early summer experienced a disconnecting phase as flow gradually reduced and stopped in various parts of the catchment before ceasing altogether. A peat wetland in the centre of the catchment exhibited both the earliest and latest stream flows.

Water quality was characteristic of a eutrophic lowland catchment and displayed spatial variations linked to catchment soils and land use. During the connecting phase, stream water quality mirrored that of groundwater and saw mobilization of dissolved organic carbon from wetland areas. In the fully connected phase, stream water became enriched with contributions from soil water and a higher nitrate load from agricultural areas. The disconnecting phase was characterized by lower flows and higher temperatures, contributing to increasingly anoxic conditions which saw nitrate reduction, mobilization of redox elements (Fe and Mn) and release of P. Intermittency caused a transition in stream water quality from hydrological process control in the connecting phase to joint control of hydrological and biogeochemical processes in the fully connected phase and then to biogeochemical process control in the disconnecting phase.

Inter-annual water quality variation was associated with hydroclimate and catchment wetness dynamics, involving flushing and accumulation. Considering intermittency as an influencing variable changed the inter-annual characteristics of flow-concentration relationships compared with the previous perennial river stage, especially for nitrate. These findings have significant implications for the ecology and management strategies in similar catchments, highlighting the need to consider the seasonal hydrological phases for effective water quality management and ecological preservation.

How to cite: Wang, F., Tetzlaff, D., Freymueller, J., and Soulsby, C.: Hydrological connectivity dynamics in a mixed land use lowland catchment drive intra- and inter-annual variation in water quality in an intermittent stream network under drought conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-153, https://doi.org/10.5194/egusphere-egu24-153, 2024.

River network is usually not a static item. More than half of global river exhibit an intermittent pattern, ceasing to flow during drought and rewetting again as the environment getting wetter seasonally. Recently, climate change has led to intensified droughts in central and southern Europe, causing even perennial streams to transition to intermittent flow patterns. Understanding and estimating to what extent drought can affect river network expansion and contraction is important and remains challenging.

This study aims to link river network dynamics and subsurface flow and to identify the potential influence of prolonged drought periods on the groundwater-river connection, and concomitant river network dynamics changes. To this end, we have coupled a fully-distributed hydrological model (mHM) with a groundwater model (Modflow) to investigate how prolonged droughts affect river network dynamics at the meso-catchment scale. The model was implemented in the Bode catchment, spanning 3200 km^² in central Germany, from 2000 to 2022, in which the period 2018-2022 is considered as drought. We calibrated the model using discharge and groundwater table depth data from 2004 to 2008. Subsequently, we validated it using observations of discharge, groundwater table depth, and river dryness and wetness from 2009 to 2022.

The results demonstrate that the model could reproduce the dryness and wetness of river networks. For the groundwater-river exchange, the length of streams with net water loss increased by 6% in the period 2018-2022 compared to 2004-2017. For the river network dynamics, temporally, total river network length shows an apparent decline. The mean and minimum river network length during recent drought years (2018-2022) decreased by 10.4% and 10.9% compared to 2004-2017, respectively. While the maximum river network of each year was reduced only by 4.37%.  Spatially, the decline of river network length mainly occurs in first and second order streams (60.2% and 25.8%). Further analysis of stream persistence shows that approximately 3% of stream reaches shift from perennial to intermittent pattern and around 8% of stream reaches transfer from intermittent pattern to permanently dry due to the drought from 2018 to 2022. This is likely not only to harm aquatic biota but to have a major impact on stream biochemistry as well.

How to cite: Li, Y., Jomaa, S., Lischeid, G., and Rode, M.: How drought can affect river network dynamics in a central Germany lowland river catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16283, https://doi.org/10.5194/egusphere-egu24-16283, 2024.

How to cite: Magee, E., Sefton, C., Parry, S., Allen, S., and England, J.: Increasing intermittence of the UK’s chalk streams into the future , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11267, https://doi.org/10.5194/egusphere-egu24-11267, 2024.