Water harvesting with Small Agricultural Reservoirs (SmAR) represents a solution for sustainable water management at a global scale. Early estimates showed that globally there were about 277,400,000 SmAR with an area of less than one hectare, and 24,120,000 water bodies between one and 10 hectares, representing more than 90% of the world’s standing water bodies. One of the most relevant challenges for the sustainable management of SmAR is represented by the loss of storage volume caused by the inflow of sediments. However, the analysis of the dynamics of sedimentation for SmAR received relatively little interest so far in the Mediterranean and on a global scale.

The purpose of this study is to implement a fully calibrated and validated model simulating the hydrology and erosion dynamics of the catchment of a SmAR in the Tuscany Region (Italy). The area is in the hilly area of Crete Senesi, about 15 km from Siena, where wine production is particularly developed, but not within the catchment of study, where the cultivation of cereals, renewal crops, and forage is practiced and there is a large grazing area. Our analysis aimed at estimating how much the rate of sediment accumulation in the reservoir would vary with the replacement of currently arable land with vineyards.

A model was implemented on the HEC-HMS software, maximizing the value of existent low-cost data (Google Earth imagery and regional erosion maps) for its validation, despite its use at a very small scale for a SmAR in a single farm. The validated model was then used for testing alternative land use scenarios in the upstream catchment, showing its flexibility for supporting decision-making over SmAR management.

The model performed with an error always below 10% on the SmAR area detected by satellite and a Nash-Sutcliffe efficiency of 0.675. Erosion values calculated with HEC-HMS were in line with the estimation made by the Tuscany region with a GIS-based procedure. The results of scenario analysis showed that the simulated land use change led to a high value of annual sediment accumulation in the reservoir (216% of the original value of erosion obtained with cereals and other crops). Such information should be considered at least at the agronomic design stage, as well as in the estimation phase of the costs of water supply, which must include the cost of the reservoir volume restoration after sediment accumulation. The approach can be replicated at the local scale in all other contexts where similar, and relatively easy-to-get, data are available.

This research was carried out within the AG-WaMED project, funded by the Partnership for Research and Innovation in the Mediterranean Area Programme (PRIMA), an Art.185 initiative supported and funded under Horizon 2020, the European Union’s Framework Programme for Research and Innovation, Grant Agreement Number No. [Italy: 391 del 20/10/2022, Egypt: 45878, Tunisia: 0005874-004-18-2022-3, Greece: ΓΓP21-0474657, Spain: PCI2022-132929]

The content of this abstract reflects the views only of the author, and the Commission cannot be held responsible for any use that may be made of the information contained therein.

How to cite: Castelli, G., Degli Innocenti, E., Pozzolini, S., Bresci, E., and Caporali, E.: Modelling the effect of land use and crop changes on water harvesting agricultural reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-936, https://doi.org/10.5194/egusphere-egu24-936, 2024.

Freshwater availability in coastal cities is severely threatened by saltwater intrusion during the dry season. Some reservoirs are typically installed in the upper reaches to regulate the temporal distribution of water resources to ensure a steady supply. However, studies quantifying this effect are limited. This study improved a framework proposed by our previous work and conducted some scenario-based experiments to evaluate this effect. The study considered the following: First, a comprehensive matrix index is developed based on the D-vine copula function and Kendall distribution transformation method (KF) using historical monthly streamflow. Then, several monthly-based management scenarios, i.e., flat, descending, ascending, convex, and concave, are designed based on the index. The scenarios provide inputs to the water supply system facing saltwater intrusion. The Zhuhai-Macao water supply system was taken as a case study. Results demonstrated that the index performed satisfactorily in devising scenarios and holistically describing the temporal streamflow distribution characteristics and hydrological wetness-dryness conditions. The security situation of scenarios followed ascending>convex>descending>flat>concave with KF=0.10 and convex>ascending>flat>descending>concave with KF=0.05. Hence, the securest scenario for regulating reservoirs was the convex pattern, which avoided shortages by 100% and improved the increment of the remaining water in reservoirs by 4.92 times under KF=0.05 and 6.13 times under KF=0.10, separately, compared to the original streamflow. The worst scenario for regulating reservoirs was the concave pattern. Moreover, the ascending pattern can also be considered as a distribution for regulation, but the long period of extremely low streamflow in the early dry season should be avoided. The scenarios experiment can be applied as a management tool to alleviate water supply pressures in coastal cities facing saltwater intrusion.

How to cite: Wu, H.: Effect of regulating upstream reservoir on water supply security facing saltwater intrusion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7491, https://doi.org/10.5194/egusphere-egu24-7491, 2024.

The compliance of environmental flows following the recommendations of the Water Framework Directive (WFD) is a crucial aspect in the management of reservoir water allocation. This issue is especially challenging in catchments with long and recurrent drought periods, such as those affected by the Mediterranean climate. There are still some gaps to be addressed by managers and water authorities. For instance, the correct definition of minimum environmental flow (MEF) to be fulfilled. These MEF values, which are set in the River Basin Management Plan (RBMP), commonly vary slightly throughout the year. Sometimes, this assumption is not accomplished because these values are above those that would have been observed under natural conditions. Therefore, in these regions it is decisive to adapt the MEF requirements to the local hydrometeorological seasonally.      

This work proposes the combination of historical streamflow and precipitation data to assess the viability of using seasonal hydrometeorological patterns in the definition of the MEF rates. For that, several monitored water bodies were analysed. Streamflow information from gauging stations and precipitation data were selected in the two main river basin districts in the South of Spain: the Guadalquivir River Basin, and the Andalusian Mediterranean Watersheds River Basin. First, for each case, we reviewed the compliance of the MEF rates analysing when these threshold values were or not achieved at the monthly scale.  In addition, we analysed the seasonal variability in terms of both precipitation and streamflow and compared these outcomes with the seasonal variations of the MEF. This analysis was carried out during 10 hydrological years, from September 2010 to August 2020.

According to our results, most of the locations were below 28% of accomplishment during the summer months. This percentage increased when the period analysed was the winter. However, this percentage was below 50% in some locations. On the contrary, only in those locations which are fed by mountain catchments, the accomplishment was fulfilled in 73-100% during the whole year. The joint seasonal analysis of precipitation and streamflow highlights that the MEF established in the RBMP were oversized in most of the cases, overlooking the precipitation patterns.

This work showed that a revision of the MEF values set by the RBMP is required. That is especially significant in locations where seasonal variations of the MEF are null or imperceptible. Our outcomes will help to set the basis for the design of a new methodology when defining MEF. Hence, this new approach will consider not only water quantity but also hydrometeorological seasonal variability as the main step to truly address water management from the perspective of the WFD. 

Acknowledgments: This work has been funded by the project TED2021-130937A-I00, ENFLOW-MED “Incorporating climate variability and water quality aspects in the implementation of environmental flows in Mediterranean catchments” with the economic collaboration of MCIN/AEI/10.13039/501100011033 and European Union “NextGenerationEU”/Plan de Recuperación, Transformación y Resiliencia.

How to cite: Contreras, E., Aparicio, J., Pimentel, R., Andreu, A., Gómez-Beas, R., Martín, L., Aguilar, C., and Polo, M. J.: Combining meteorological and streamflow information for defining minimum environmental flow requirements in Mediterranean catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8692, https://doi.org/10.5194/egusphere-egu24-8692, 2024.

The year-end water level of multi-year regulation reservoirs is key in harmonizing current-year and future power generation benefits. Taking the multi-year regulating Longyangxia Reservoir and Liujiaxia Reservoir in the upper reaches of the Yellow River as a case study, a multi-objective stochastic optimization model for cascade reservoirs considering the uncertain inflow was established. Then, the best scheme from the Pareto solution set of the current-year power output and the year-end water level was obtained based on the TOPSIS decision-making method. Finally, the effects of runoff frequency and initial water level on year-end water level and power output were investigated, and the reliability of year-end expected water level on multi-year power output was verified. The results show a competitive relationship between the year-end expected water level of Longyangxia Reservoir and the annual expected power output of Longyangxia Reservoir and Liujiaxia Reservoir under the uncertainty inflow scenarios. The lower the frequency of runoff and the higher the year-start water level to Longyangxia Reservoir, the higher the year-end water level of Longyangxia and the higher the power output of Longyangxia Reservoir and Liujiaxia Reservoirs. The optimal year-end water level of Longyangxia Reservoir calculated by the stochastic optimization model should be controlled between 2580~2590 meters, which greatly reduces the range of year-end water level under the current dispatching mode. When the optimal year-end expected water level obtained by stochastic optimization is used to control Longyangxia Reservoir, the reliability of guaranteeing the power generation benefit is above 98%.

Keywords: multi-year regulating reservoir; year-end water level; uncertainty; stochastic optimal operation

How to cite: Li, J., Zheng, J., Li, H., and Wang, Y.: Study on year-end water level optimization of  multi-year regulation reservoirs under uncertain inflow conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8500, https://doi.org/10.5194/egusphere-egu24-8500, 2024.

Retention of sediment in lakes and reservoirs is a major problem that impacts drinking water supplies, irrigation, recreation, hydropower production, and flood control globally. Sediment loads to lakes and reservoirs are likely to increase due to changing climate, e.g. increases in high intensity precipitation events. However, this impact is often not considered in large scale hydrological assessments of climate changes.

An ongoing challenge with assessing reservoir sedimentation at a large scale is that many basins are ungauged, and information about sediment management and decision making is not available. Large-scale dynamic hydrological models are fortunately becoming more commonly established as tools not only for flood forecasting and climate impact analyses, but also for estimating time-dynamic water fluxes and their transport into sea basins. One such tool is the dynamic, semi-distributed, process-based rainfall-runoff and water quality model, Hydrological Predictions for Environment (HYPE, see Lindström et al., 2010; https://hypeweb.smhi.se/).

While many hydrological models do not explicitly consider the sediments accumulating in reservoirs, HYPE was recently updated to dynamically simulate (1) the effect of sediments on the available volume of lakes and reservoirs and (2) selected sediment management strategies. The new routines were tested on several reservoirs globally using different types of data for calibration: instream sediment concentrations (Banja in Albania), storage capacity loss (Enguri in Georgia), and upstream sediment yield (dams in Greater uMngeni River Basin in South Africa). The current annual rate of storage capacity loss varied greatly among cases (0.004-4.15%). The routines were then incorporated into a pan-European HYPE model, E-HYPE (Brendel et al., 2023), and calibrated against observed sediment concentrations. The change in storage capacity loss in European reservoirs and lakes was then evaluated for 3 climate models. We present current and future losses of lake and reservoir storage and analyze sediment regimes in water bodies with water management structures such as hydropower or drinking water reservoirs.

Lindström, G., Pers, C., Rosberg, J., Strömqvist, J., Arheimer, B., 2010. Development and testing of the HYPE (Hydrological Predictions for the Environment) water quality model for different spatial scales. Hydrol. Res. 41, 295–319. https://doi.org/10.2166/nh.2010.007

Brendel, C. E., Capell, R., Bartosova, A. (2023) To tame a land: Limiting factors in model performance for the multi-objective calibration of a pan-European, semi-distributed hydrological model for discharge and sediments. Journal of Hydrology: Regional Studies, 50(2023) 101544. https://doi.org/10.1016/j.ejrh.2023.101544

How to cite: Bartosova, A., Brendel, C., and Capell, R.: Fate of reservoir storages due to sedimentation in changing climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10225, https://doi.org/10.5194/egusphere-egu24-10225, 2024.

The Allier River is a tributary of the Loire, the longest river in mainland France. It covers a watershed of 14,310 km². To maintain an objective flow in the Middle Loire, two reservoirs are used to release water during summer including Naussac on the Allier River (190 hm³). These operations are monitored by the Loire River Basin Authority (Établissement Public Loire). The 2022 and 2023 droughts in France highlighted the vulnerability of Naussac water supply in summer. This risk will be more important in the future, as global warming leads to lower flows in the watershed.

To evaluate the impacts of global change on electricity production across the Loire watershed at Saumur (81,200 km²), a framework that encompasses water usage demand (considering water withdrawals) in hydrological simulations has recently been developed. We propose to complete this framework with the introduction of hydraulic structure management rules (Fig.1), to evaluate the long-term performance of the low water level support system for two future timeframes, 2035-2065 (mid-term) and 2070-2099 (long-term), relative to the current climate (1976-2005).

Our analysis focuses on the management of the Naussac dam and the provision of low-water support for the Allier River [2]. In wet periods, Naussac can be filled in three ways: via natural inflows from the Donozau river, a detour on the Chapeauroux river, and pumping into the Allier. In dry periods, it provides low-water support for the Allier at various strategic points, known as nodal points, to satisfy the multiple uses of water downstream (agriculture, drinking water supply, etc.). Explicit integration of these constraints at nodal points allows for global performance analysis.

The Naussac management model was validated over the historical period, then projected into future climates using 4 climate models from CMIP5, forced by the RCP 8.5 greenhouse gas emissions scenario. The drop in flows forecasted for the end of the century would lead to more frequent interruption in low-water support, that can be highlighted with several indicators analysis [3]. This situation is characterized by a drastic fall in the average stock of the Naussac reservoir over the year by the end of the 21st century (Fig.2). Management rules can be adapted to a certain extent and help reduce vulnerability of the low-water support, but limited by the need to maintain downstream water uses and the good ecological status of the hydro system.

Figure 1: Schematic view of the water management system of Naussac dam.

Figure 2: Model validation over the historical (top) period and visualization of average stock in future (bottom).

References:

[1] Sauquet, E., Robin, Y., Corre, L., Marson, P., Bernus, S., Projections climatiques régionalisées : Correction de biais et changements futurs, Explore2, Recherche Data Gouv, V2, 2022.

[2] Sonnet, O., Etude HMUC : étude d’adaptation du mode de gestion du barrage de Naussac sous l’effet du changement climatique, Phase 1, Technical report, Etablissement Public Loire, 2016.

[3] Francois, B., Thèse : gestion optimale d'un réservoir hydraulique multiusages et changement climatique. Modèles, projections et incertitudes : Application à la réserve de Serre-Ponçon, 2013.

How to cite: Vermeil, V., Debein, C., Monteil, C., Hendrickx, F., Zaoui, F., Samie, R., and Lamouroux, R.: Assessing long-term performance of a low water level support system under climate change using influenced streamflows models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11425, https://doi.org/10.5194/egusphere-egu24-11425, 2024.

River impoundments play a substantial role in altering the global water cycle and terrestrial water storage (TWS) dynamics. In light of the vulnerability of the global water cycle to both climate change and human activities, there is a pressing need for an integrated approach to water management that combines scientific insights with sustainable reservoir operation strategies. In this context, the integration of the advanced computational model Noah-MP and an innovative satellite-based reservoir operation scheme called HyMAP offers a comprehensive understanding of the reservoir dynamics of Tawa reservoir situated along the Narmada River in India. To accurately depict absolute water storage, a ground-based lake bathymetry is incorporated into the analysis, merging it with global satellite-based topography. Additionally, radar altimetry data is integrated into the hydrodynamic model to serve as a proxy for reservoir operation practices. Comparing the results against an idealized naturalized system (assuming no anthropogenic impacts) during the period from 2005 to 2022, the study reveals that reservoir operation has a substantial impact on water elevation, extent, storage, and outflow. These operational practices exert control over lake dynamics and TWS, emphasizing the need for a sustainable and informed approach to reservoir management.

How to cite: sharma, P. and saharia, M.: "Reservoir Dynamics: Assessing Sustainable Operations' Impact on Water Cycle", EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18597, https://doi.org/10.5194/egusphere-egu24-18597, 2024.

Globally there are over 24,000 dams that greatly alter river connectivity and streamflow regimes of the world’s large rivers. To capture the impact of dams, global hydrological models implement simplified reservoir operations that use modelled inflow, static storage capacity values, and downstream demand to calculate reservoir releases and better understand large-scale streamflow dynamics. According to Steyaert et al., 2023, these approaches typically overestimate the amount of water stored in reservoirs, smooth out the seasonality in storage, and may miss long term trends. All of which can underestimate the impact on streamflow regimes as the operations are not necessarily derived from historic time series. To assess the importance of reservoir operations on global streamflow regimes, we update the number of reservoirs in the PCRGLOBWB 2.0 hydrologic model from 6,000 to 24,000 using the georeferenced global dams and reservoirs dataset (GeoDAR (Wang et al., 2022)) and derive dynamic storage thresholds using freely accessible remotely sensed storage data and a new reservoir algorithm developed by Turner et al., 2021. We obtained the reservoir specific parameters required for the Turner algorithm using a ML based approach to enable global simulations of all 24,000 dams. We also employ a sensitivity analysis across multiple command areas (250, 650 and 1100 km) to assess the impact reservoirs have on the global streamflow and downstream water demand. Preliminary results in the Rhine basin show that increasing the number of dams and using data derived methods provides more realistic streamflow regimes. We observe an improvement in the KGE of discharge simulations from 0.43 to 0.67, also reducing the bias from -2012.23 to -316.94 compared to the old reservoir implementation currently used in PCR-GLOBWB 2.0. This significant improvement in model performance highlights the importance of observation derived rule curves for reservoir management in global hydrological models.

How to cite: Steyaert, J., Wanders, N., and Bierkens, M.: ML-derived reservoir operations for 24,000 dams implemented in a global hydrological model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11194, https://doi.org/10.5194/egusphere-egu24-11194, 2024.

Uncoordinated development plans in rivers upstream coupled with climate change and variability have resulted in hydrological disturbances and their consequent social conflicts and environmental issues in downstream. Dams and hydrosystems are known as one of the main causes of such issues, however, they can be victimized by upstream developments themselves which result in failure in operation, fulfilling historical downstream allocations, and wasting large amounts of financial resources due to multiple investments. Giving some critical examples from Iran, an arid and semi-arid country, such failures can be observed in Karkheh and Sefidrud dams with 56 and 65% inflow reduction respectively. The impacts and consequences of such mismanagements will be demonstrated in this study. For this purpose, a new concept and methodology called “Mirage Water” is defined as the downstream flow deficit caused by upstream water development ignoring historical allocations. Firstly, the year of abrupt change (YAC) in precipitation and flow time series is assessed by the Pettiit test and then the annual flow characteristics before and after that abrupt change will be compared. The contribution level of anthropogenic activity and precipitation deficit in flow reduction is estimated using Simple linear regression and double mass curve methods. Meanwhile, the meteorological and hydrological drought is assessed using SPI and SDI and hybridized. Finally, the river impact in critical stations is presented. The results show that the YAC in Sefidrud’s inflow happened after its construction year due to a 57% contribution of anthropogenic activities. In the other case, Karkheh experienced the YAC in its inflow 2 years before the construction year with 44% anthropogenic impact.

How to cite: Ghadimi, S., Sharifi Garmdareh, A., and Torabi Haghighi, A.: What you see is mirage: even dams can die of thirst, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19951, https://doi.org/10.5194/egusphere-egu24-19951, 2024.

How to cite: Omer, A., Elagib, N., Wada, Y., Pokhrel, Y., and Kim, H.: Toward Holistic Perspective on Dam Efficacy in Transboundary Hydro-Extremes Management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8627, https://doi.org/10.5194/egusphere-egu24-8627, 2024.