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Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In regions characterized by a high concentration of small reservoirs, there is often public debate about the effectiveness of these structures in locally adapting to and mitigating drought impacts, bearing in mind their potential to modify or induce drought events in downstream areas. In this study, we investigated the influence of a Dense Network of Small Reservoirs (DNR) on the emergence and intensification of drought impacts at catchment scale, as well as their local social benefits. This analysis was based on the Socio‐Hydrological‐Agricultural‐Reservoir (SHARE) model, specially developed for this purpose, with a medium‐sized catchment in the semi‐arid region of Brazil as a case study. We identified that, while a DNR can prolong the effects of a hydrological drought on storage in a large strategic reservoir at the catchment outlet by obstructing surface‐runoff connectivity, it plays a crucial role in mitigating drought impacts at a local level. Specifically, the presence of small reservoirs has the potential to boost local agricultural production by up to 5 times compared to scenarios without these structures. In addition, our simulation results suggest there is a notable reduction in the need for emergency water distribution by water trucks in the presence of a DNR. This study highlights the need for a balanced approach to implementing public policies, weighing the local benefits of small reservoirs against the possible downstream impacts on large reservoirs. Plain Language Summary: This study analyzed the impact of a dense network of small reservoirs in a semi‐arid region of Brazil on drought effects. Although there is criticism about the use of these structures because they can influence drought events in neighboring areas, our results showed that, locally, these reservoirs are essential for mitigating the impacts of drought. They may prolong the drought in large reservoirs, but they play a crucial role in reducing local impacts, increasing agricultural production by up to five times. In addition, the presence of these reservoirs considerably reduces the need for emergency water distribution by water trucks. The study highlights the importance of a balanced approach when implementing public policies, considering the local benefits of small reservoirs in relation to the possible impacts on more distant areas. Key Points: We explore the pro's and con's of small reservoirs as drought coping strategyEvaporation puts more pressure on surface water storage in semi‐arid regions than the demands of small farmersSmall reservoirs boost the local agricultural production up to five times while reducing the need for emergency water supply [ABSTRACT FROM AUTHOR]

Abstract In regions characterized by a high concentration of small reservoirs, there is often public debate about the effectiveness of these structures in locally adapting to and mitigating drought impacts, bearing in mind their potential to modify or induce drought events in downstream areas. In this study, we investigated the influence of a Dense Network of Small Reservoirs (DNR) on the emergence and intensification of drought impacts at catchment scale, as well as their local social benefits. This analysis was based on the Socio‐Hydrological‐Agricultural‐Reservoir (SHARE) model, specially developed for this purpose, with a medium‐sized catchment in the semi‐arid region of Brazil as a case study. We identified that, while a DNR can prolong the effects of a hydrological drought on storage in a large strategic reservoir at the catchment outlet by obstructing surface‐runoff connectivity, it plays a crucial role in mitigating drought impacts at a local level. Specifically, the presence of small reservoirs has the potential to boost local agricultural production by up to 5 times compared to scenarios without these structures. In addition, our simulation results suggest there is a notable reduction in the need for emergency water distribution by water trucks in the presence of a DNR. This study highlights the need for a balanced approach to implementing public policies, weighing the local benefits of small reservoirs against the possible downstream impacts on large reservoirs.

Early warning of safety risks downstream of small reservoirs is directly related to the safety of people's lives and property and the economic and social development of the region. The lack of data and low collaboration in downstream safety management of small reservoirs makes the existing safety risk warning methods for small reservoirs no longer fully applicable. The data from flood control and drought relief departments, small reservoir operation and management departments, etc., are used comprehensively. A machine learning model suitable for a large number of samples, a small amount of data, and the condition of incomplete information is applied and innovated, and from the holistic perspective of 'upstream reservoir—downstream region', the safety risk factors of the upstream reservoir are identified with the help of the Granger causality test. The risk losses of the disaster behavior are predicted with the three-dimensional k ~ ε two-equation model coupled with the VOF (Volume of fluid) method and the neural network model. The safety risk dynamics prediction, the prediction of the disaster-causing environment, and the prediction of the risk losses are integrated to construct the early warning method of the downstream safety risk of small reservoirs, and the simulation effect is verified with the example of the J Reservoir. The results show that the model can clarify the causal relationships and time lag dependencies between hydro-meteorological factors and the water level of small reservoirs, and calculate the inundation depth, inundation range, and flood velocity downstream of small reservoirs. The downstream safety warning model of small reservoirs constructed in this article can effectively integrate upstream and downstream information, further improve the timeliness and accuracy of warning, and provide a reference for downstream safety risk management of small reservoirs. [ABSTRACT FROM AUTHOR]

There are an estimated 800,000 small reservoirs globally with a range of uses. Given the collective importance of these reservoirs to water resource management and wider society, it is essential that we can monitor and understand the hydrological dynamics of ungauged reservoirs, particularly in a changing climate. However, unlike large reservoirs, continuous and systematic hydrological observations of small reservoirs are often unavailable. In response, this study has developed a retrieval framework for water levels of small reservoirs using a deep learning algorithm and remotely sensed satellite data. Demonstrated at four reservoirs in California, satellite imagery from both Sentinel-1 and Sentinel-2 along with corresponding water level field measurements was collected. Post-processed images were fed into a water level inversion convolutional neural network model for water level inversion, while different combinations of these satellite images, sampling approaches for training/testing data, and attention modules were used to train the model and evaluated for accuracy. The results show that random sampling of training data coupled with Sentinel-2 satellite imagery was generally the most accurate initially. Performance is improved by incorporating a channel attention mechanism, with the average R2 increasing by 8.6% and the average RMSE and MAE decreasing by 15.5% and 36.4%, respectively. The proposed framework was further validated on three additional reservoirs in different regions. In conclusion, the retrieval framework proposed in this study provides a stable and accurate methodology for water level estimation of small reservoirs and can be a powerful tool for small reservoir monitoring over large spatial scales. [ABSTRACT FROM AUTHOR]

There are an estimated 800,000 small reservoirs globally with a range of uses. Given the collective importance of these reservoirs to water resource management and wider society, it is essential that we can monitor and understand the hydrological dynamics of ungauged reservoirs, particularly in a changing climate. However, unlike large reservoirs, continuous and systematic hydrological observations of small reservoirs are often unavailable. In response, this study has developed a retrieval framework for water levels of small reservoirs using a deep learning algorithm and remotely sensed satellite data. Demonstrated at four reservoirs in California, satellite imagery from both Sentinel-1 and Sentinel-2 along with corresponding water level field measurements was collected. Post-processed images were fed into a water level inversion convolutional neural network model for water level inversion, while different combinations of these satellite images, sampling approaches for training/testing data, and attention modules were used to train the model and evaluated for accuracy. The results show that random sampling of training data coupled with Sentinel-2 satellite imagery was generally the most accurate initially. Performance is improved by incorporating a channel attention mechanism, with the average R2 increasing by 8.6% and the average RMSE and MAE decreasing by 15.5% and 36.4%, respectively. The proposed framework was further validated on three additional reservoirs in different regions. In conclusion, the retrieval framework proposed in this study provides a stable and accurate methodology for water level estimation of small reservoirs and can be a powerful tool for small reservoir monitoring over large spatial scales.

Early warning of safety risks downstream of small reservoirs is directly related to the safety of people’s lives and property and the economic and social development of the region. The lack of data and low collaboration in downstream safety management of small reservoirs makes the existing safety risk warning methods for small reservoirs no longer fully applicable. The data from flood control and drought relief departments, small reservoir operation and management departments, etc., are used comprehensively. A machine learning model suitable for a large number of samples, a small amount of data, and the condition of incomplete information is applied and innovated, and from the holistic perspective of ‘upstream reservoir—downstream region’, the safety risk factors of the upstream reservoir are identified with the help of the Granger causality test. The risk losses of the disaster behavior are predicted with the three-dimensional k~ε two-equation model coupled with the VOF (Volume of fluid) method and the neural network model. The safety risk dynamics prediction, the prediction of the disaster-causing environment, and the prediction of the risk losses are integrated to construct the early warning method of the downstream safety risk of small reservoirs, and the simulation effect is verified with the example of the J Reservoir. The results show that the model can clarify the causal relationships and time lag dependencies between hydro-meteorological factors and the water level of small reservoirs, and calculate the inundation depth, inundation range, and flood velocity downstream of small reservoirs. The downstream safety warning model of small reservoirs constructed in this article can effectively integrate upstream and downstream information, further improve the timeliness and accuracy of warning, and provide a reference for downstream safety risk management of small reservoirs.

Small reservoirs play an important role in providing water to rural communities. Increased construction of small reservoirs to mitigate the effects of droughts leads to a High-density Reservoirs Network (HdRN) of small reservoirs, which can potentially modify the streamflows both in dry and wet periods. However, there is a lack of understanding of the interannual behavior of flow retention and the impact of future increases in the number of small reservoirs, mainly for HdRN in dryland catchments. This research aims to determine the possible impact of the increase in the number of small reservoirs on dry hydrological networks, evaluating the annual flows generated at the outlet of a dryland watershed for scenarios with different densities of small reservoirs (number of reservoirs per area). The study area was the Conceição river catchment (3347 km2) in the semiarid of Brazil. The hydrological model of the study area was developed in SWAT. The model obtained appropriate results for daily streamflows, with values of 0.63, 0.81, and 0.53% for NSE, KGE, and PBIAS, respectively. The current density of small reservoirs in the region was estimated at 0.068 reservoirs per square kilometer (res/km2). Eight expansion scenarios were defined for densities between 0.1 res/km2 and 3.0 res/km2. The results showed that the influence of the HdRN on runoff reduction mostly occurs for a probability of exceedance between 1% and 10% of month flows and is very small for months with very high peaks of flow. The reduction in the outlet flow due to the increase in the number of small reservoirs was stronger during dry years (up to 30%) than during wet years (up to 8%), and it tended to increase in years with a consecutive lack of rain (from about 7% in the first year to about 20% in the last year and in the worst scenario), which may intensify the period of extended droughts. This research provides insights about the impact of the increase in the number of small reservoirs on the interannual variability of flow retention, and the understanding of the influence of small reservoirs on runoff reduction may help water resources agencies better prepare for hydrologic extremes (droughts and floods). [ABSTRACT FROM AUTHOR]

Copyright of Eurasian Journal of Ecology is the property of Al-Farabi Kazakh National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water scarcity is a growing challenge in semi-arid and sub-humid areas. There are over 2000 small reservoirs (SRs) with storage capacities of up to 1 × 106 m3 across West Africa's dry areas. Based on a comprehensive literature review, we found strong evidence that SRs enable improved food security, livelihoods, and income diversification through fishing and livestock production. However, their productivity is far below their potential. Evidence on water quantity and quality is scattered, making deriving conclusions difficult. Review findings suggest that, unlike large dams, SRs have minimal impact on water balance and rainfall-runoff. There is, therefore, considerable potential to develop more SRs. However, high rates of sedimentation substantially reduce reservoir storage capacity. Poor irrigation management and agronomic practices also contribute to low productivity. Water quality is not systematically monitored, so SRs can increase health risks such as malaria and schistosomiasis. With the intensification of settlements, livestock, and agriculture around the reservoirs, it is critical to improve water quality and quantity monitoring. We conclude that SRs are important nature-based solutions, but need more investment to support the climate-proofing of agriculture and livelihoods. We recommend governments develop long-term small reservoir support programs to strengthen local capacities to manage the reservoirs and their watersheds sustainably. [ABSTRACT FROM AUTHOR]

The paper presents an attempt to forecast heavy metal pollution of sediments of four designed reservoirs in southern Poland. For this purpose, concentration of dissolved heavy metals (lead, cadmium and nickel) was determined in water of watercourses on which the designed reservoirs will be constructed and also in sediments and water flowing into six reservoirs that are already in use. Based on the results of the heavy metal concentrations of six exploited reservoirs, a relationship was developed between heavy metal concentration in the sediment as a function of the concentration of these metals in the inflowing water. Using these relationships, the forecast concentrations of these metals in the sediments of the designed reservoirs were estimated. The mean concentrations of these metals in the planned reservoirs were 20.5 mg.kg-1 for lead, 3.4 mg.kg-1 for cadmium and 14.8 mg.kg-1 for nickel. No dangerous pollution of analyzed metal of water inflows to the planned reservoirs was found. The calculated geoaccumulation index indicates that in terms of the lead and nickel concentrations, sediments in the planned reservoirs will be unpolluted to moderately polluted, while for cadmium concentrations - they will be moderately to strongly polluted. [ABSTRACT FROM AUTHOR]

The topmouth gudgeon Pseudorasbora parva Temminck et Schlegel, 1846, has become one of the most widespread piscivores on the Eurasian continent [1]. The natural habitat of the species is inland water bodies of Japan, Taiwan, Hainan, China, and Korea. The species dispersed into the Balkhash-Ili basin during large-scale acclimatization of herbivorous fish from water bodies of China. The article presents the results on the study of the variability of morphological and biological parameters of the Amur chebok Pseudorasbora parva from different types of reservoirs in the Balkhash basin. Materials for the studies were caught from the irrigation canal near the Bakanas settlement, from the pond near the Beskainar settlement and from Lake Alakol. According to the results of the trapping, the wide distribution of this species in the most different conditions was established. At comparison of dimensional – weight parameters of 3 samples from the investigated reservoirs, the maximal values for a sample from the reservoir of settlement Beskainar are established. The big variability is shown in position and the sizes of dorsal, pectoral, pelvic fins. According to the position of anal fin, the sample from the pond near Beskainar differs from the other two. Significant differences in the shape of the head and body were also found between the samples studied. [ABSTRACT FROM AUTHOR]

The names of 152 river courses and water bodies located in the same watershed in central Burkina Faso have been inventoried by the authority charged with implementing the Integrated Water Resources Management scheme. The purpose was to set up a base for a nomenclature of the hydrographic network. 125 of these water bodies are named in the vernacular (in mòoré). The meaning of these toponyms is indicated in French in the technical report which summarizes the survey results. This sample offers the possibility of comparing the meaning of the names given to natural ('river courses') and artificial ('water bodies', i.e. dams) features of the hydrographic network in this watershed. Water' names were first intuitively classified on a logical basis. In fine, the database and resulting classification were discussed with three independent reviewers who were experts of the region and fluent in mòoré. Seven classes were identified, with river courses being present in each of them while small reservoirs occurred in only four. Clearly, water names vary, as do the perceptions local inhabitants have of these water bodies. These social representations of the two groups of these water bodies, considered here by our toponymic analysis, make a clear distinction between natural river courses, which are familiar and useful sites, and dams that are generally anonymous or even neglected. Explanations relating to the more or less claimed appropriation of artificial reservoirs and the methods of their development may be suggested. The study highlights the importance of involving anthropological studies in interdisciplinary projects focused on water resources. [ABSTRACT FROM AUTHOR]

Evaporative losses from small seasonal water reservoirs in semiarid regions may significantly diminish storage and water availability to rural communities. Motivated by finding effective and economically feasible measures for suppressing evaporation, we study the efficacy of self‐assembling floating covers in suppressing evaporation under field conditions and potential ecological ramifications of the covers. We conducted a multi‐season study with eight identical small reservoirs (13.5 m2 area and 1.5 m deep) using ethylene‐vinyl acetate foam disks (200 mm in diameter, 15 mm thick) in white and black to cover six reservoirs (cover fraction of 91%), leaving two uncovered reservoirs for control. Physical attributes such as evaporative losses, radiative balance, temperature, and heat fluxes were measured and compared with modeling results. Evaporation suppression under field conditions ranged between 65% and 80% in the summer. Despite significant differences in energy partitioning, evaporation from white and black disks were relatively similar (∼20% for white and ∼30% evaporation for black disks compared to uncovered reservoir). Replacing black disks with water filled black polyethylene balls improved suppression efficiency and diminished seasonal variations (∼80% suppression irrespective of season). We developed a physically based model to describe and extend the experimental findings by exploring effects of reservoir management regimes on evaporation and to optimize cover and reservoir characteristics for different climatic conditions. Key Points: A multi‐season field experiment using eight small reservoirs revealed 65%–80% reduction in evaporation using floating disks and spheresCover color had small effect on evaporation suppression; black spheres were most efficient followed by white and black disksIn contrast to white covers with higher suppression efficiency in summer, black covers did not show seasonality in evaporation suppression [ABSTRACT FROM AUTHOR]

Water scarcity is a growing challenge in semi-arid and sub-humid areas. There are over 2000 small reservoirs (SRs) with storage capacities of up to 1 × 106 m3 across West Africa’s dry areas. Based on a comprehensive literature review, we found strong evidence that SRs enable improved food security, livelihoods, and income diversification through fishing and livestock production. However, their productivity is far below their potential. Evidence on water quantity and quality is scattered, making deriving conclusions difficult. Review findings suggest that, unlike large dams, SRs have minimal impact on water balance and rainfall-runoff. There is, therefore, considerable potential to develop more SRs. However, high rates of sedimentation substantially reduce reservoir storage capacity. Poor irrigation management and agronomic practices also contribute to low productivity. Water quality is not systematically monitored, so SRs can increase health risks such as malaria and schistosomiasis. With the intensification of settlements, livestock, and agriculture around the reservoirs, it is critical to improve water quality and quantity monitoring. We conclude that SRs are important nature-based solutions, but need more investment to support the climate-proofing of agriculture and livelihoods. We recommend governments develop long-term small reservoir support programs to strengthen local capacities to manage the reservoirs and their watersheds sustainably.

Purpose: This paper investigates the morphological and location features influencing the sediment texture of small reservoirs located within the embanked floodplain of a lowland river. Bed and suspended loads deposited in these reservoirs, settle as sediments, whose texture could indicate factors shaping processes within the embanked floodplains. Materials and methods: Sediment samples were extracted from three sections of each of 10 reservoirs and measured with respect to the grain size distribution. The statistical analyses determined factors affecting the texture and enabled the comparison of the reservoirs and their initial, middle, and final sections. Results and discussion: Factors such as the length of the reservoir, its area, the distance from the river, the width of the embankment area, and the location along the river were found to have a negligible effect on proportion of sediment fractions. The maximum depth and the angle between the reservoir axis and the riverbed were the only two characteristics that notable contributed to the differences in the sediment texture. In deeper reservoirs the content of sand fraction was considerably higher, while simultaneously the share of silt was lower. The angle value influenced the sediment texture of each reservoir in general as well as considering their final parts. As the angle increased, the sand content increased as well, whereas the shares of silt and clay decreased. Conclusions: The maximum depth and the angle between the river and the reservoir can be considered as the key determinants of the sediment texture in small floodplain reservoirs. [ABSTRACT FROM AUTHOR]

Fulfilling both "Water and soil conservation" and "Integrated rural development" objectives, hillside reservoirs are very popular components of water and/or rural management strategies. In Central Tunisia, more than 800 reservoirs have been built since the 1950s. These have been the subject of an abundant literature by both social and physical scientists. However, this literature, which is highly segmented and often centred on the technical and economic assessment of development programs, does not help understand the different logics at work in the appropriation of these technical objects by the different actors involved. To achieve this goal, our research based on a "sociohydrological negotiation", articulates the methods and research questions of hydrology and anthropology on a same case study in Central Tunisia. An initial survey of water use and management practices around hillside reservoirs in the Merguellil Catchment revealed the wide variety of the infrastructures and the multiple functions they fulfil. These initial observations underpinned the process of negotiating an interdisciplinary framework to analyze the social, physical and technical dimensions of hillside reservoirs. To trace the history of watershed development policies implemented in the Merguellil Catchment, we first examined the multiple embedded logics underlying Tunisian hillside reservoir planning. This led to the production of "sociohydrological narratives" for four hillside reservoirs that both combined and enabled us to analyze the inhabitants' own accounts of their reservoir history. This ethnographical material was then examined through the lense of a "resource making process". Considering the way in which hydraulic objects function in a landscape that is both socio-political and hydrological enabled us to analyze the different aspects of this resource making process, from water valuation to the production of "hydraulic localities". • Interdisciplinary field research reveals the multiple functions of hillside reservoirs. • Tunisian hillside reservoirs are unreliable hydrological and economic resources. • Hillside reservoirs support a process of relational resource making. • Sociohydrological negotiations yield new insights into water-society relations. [ABSTRACT FROM AUTHOR]

Specific hydrological characteristics of small reservoirs and insufficiency of data on them determine the need for their integrate investigation to reveal the patterns of their ecosystems formation that could help to estimate their state in the future monitoring. The article presents the data on water chemistry and the main biological components (phyto – and zooplankton, zoobenthos, vascular plants, and mosses) of three small reservoirs situated in middle taiga subzone of Komi Republic. It was established that hydrochemical characteristics and flora and fauna species composition reflect regional specificity of the studied water bodies. Present stage of development of the reservoirs ecosystems was identified based on the analysis of the community structure. Characteristics of flora and fauna spatial distribution along the water body were studied. Ecological states of the investigated ecosystems were evaluated. Our results can be applied for prognosis of development of small river-type reservoirs

Distributed attenuation in flood management relies on small and low-impact runoff attenuating features variously distributed within a catchment. Distributed systems of reservoirs, natural flood management, and green infrastructure are practical examples of distributed attenuation. The effectiveness of attenuating features lies in their ability to work in concert, by reducing and slowing runoff in strategic parts of the catchment, and desynchronizing flows. The spatial distribution of attenuating features plays an essential role in the process. This article proposes a framework to place features in a hydrologic network, group them into spatially distributed systems, and analyze their flood attenuation effects. The framework is applied to study distributed systems of reservoirs in a rural watershed in Iowa, USA. The results show that distributed attenuation can be an effective alternative to a single centralized flood mitigation approach. The different flow peak attenuation of considered distributed systems suggest that the spatial distribution of features significantly influences flood magnitude at the catchment scale. The proposed framework can be applied to examine the effectiveness of distributed attenuation, and its viability as a widespread flood attenuation strategy in different landscapes and at multiple scales.

• Small lakes support agricultural diversification and rise in fruit tree farming. • Landsat time series characterise water availability of multiple ungauged lakes. • Water scarcity and unreliability on 86% of lakes impedes agricultural intensification. • Economic water scarcity and mismanagement further constrain agricultural development. • Interdisciplinary multi-scalar approach improves understanding of socio-hydrosystems. Millions of small reservoirs built across semi-arid areas present a potential to support agricultural livelihoods of rural smallholders. The scale and geographical dispersion of these multiple lakes restrict the understanding of these coupled human-water systems and the identification of adequate strategies to support riparian farmers. This research developed a multi-scalar interdisciplinary approach to characterise the hydrological and wider drivers of agricultural water use around multiple small reservoirs in semi-arid central Tunisia. The combination of field surveys, quantitative questionnaires and qualitative, semi-structured interviews confirmed minimal withdrawals, but highlighted the diversification of practices, the rise in fruit farming and peripheral benefits generated here by the development of 56 lakes. 48% of lakes provide residual benefits for the occasional watering of on average 300 fruit trees and support to downstream wells exploited for irrigation. A further 13 lakes (23%) provide high levels of benefits (900 fruit trees each), albeit with low equity, supporting essentially established farmers. The analysis of surface water assessments every 8 days from Landsat 5–8 imagery over 1999–2014, provides unprecedented insights into the significant water scarcity and unreliability that impedes agricultural intensification on 86% of small lakes. Limited storage capacities and prolonged droughts highlight the need for small reservoirs in this climatic context to retain a supplementary irrigation objective and not strive to support widespread intensification of irrigated practices. Many farmers lack the capabilities to increase their withdrawals and suffer physical and economic water access difficulties, mismanagement, compounded through limited and short-term government assistance. Individual successes resulted from farmers' economic resilience and means to secure alternate water supplies during dry spells. [ABSTRACT FROM AUTHOR]

Abstract The number of small reservoirs has increased due to their reduced cost, the availability of many favourable locations, and their easy access due to proximity. The cumulative impacts of such small reservoirs are not easy to estimate, even when solely considering hydrology, which is partially due to the difficulty in collecting data on the functioning of such reservoirs. However, there is evidence indicating that the cumulative impacts of such reservoirs are significant. The aim of this article is to present a review of the studies that address the cumulative impacts of small reservoirs on hydrology, focusing on the methodology and on the way in which these impacts are assessed. Most of the studies addressing the hydrological cumulative impacts focused on the annual stream discharge, with decreases ranging from 0.2% to 36% with a mean value of 13.4 % ± 8 % over approximately 30 references. However, it is shown that similar densities of small reservoirs can lead to different impacts on stream discharge in different regions. This result is probably due to the hydro-climatic conditions and makes defining simple indicators to provide a first guess of the cumulative impacts difficult. The impacts also vary in time, with a more intense reduction in the river discharge during the dry years than during the wet years. This finding is certainly an important point to take into consideration in the context of climate change. Two methods are mostly used to estimate cumulative impacts: i) exclusively data-based methods and ii) models. The assumptions, interests and shortcomings of these methods are presented. Scientific tracks are proposed to address the four main shortcomings, namely the estimation of the associated uncertainties, the lack of knowledge on reservoir characteristics and water abstraction and the accuracy of the impact indicators. Graphical Abstract Highlights • The number of small dams is still increasing and is approaching 39 dams per square kilometre. • Small dams lead to a decrease in annual stream discharge of 13% ± 8%. • Cumulative impacts cannot be estimated using simple indicators. • Cumulative impacts are difficult to estimate and are most often quantified from modelling. • The lack of information on small reservoir characteristics is a real shortcoming for properly estimating their cumulative impacts. [ABSTRACT FROM AUTHOR]

Small reservoirs (SRs) are essential water storage infrastructures for rural populations of Sub-Saharan West Africa. In recent years, rapid population increase has resulted in unprecedented land use and land cover (LULC) changes. Our study documents the impacts of such changes on the water quality of SRs in Burkina Faso. Multi-temporal Landsat images were analyzed to determine LULC evolutions at various scales between 2002 and 2014. Population densities were calculated from downloaded 2014 population data. In situ water samples collected in 2004/5 and 2014 from selected SRs were analyzed for Suspended Particulate Matter (SPM) loads, an integrative proxy for water quality. The expansion of crop and artificial areas at the expense of natural covers controlled LULC changes over the period. We found a very significant correlation between SPM loads and population densities calculated at a watershed scale. A general increase between the two sampling dates in the inorganic component of SPM loads, concomitant with a clear expansion of cropland areas at a local scale, was evidenced. Results of the study suggest that two complementary but independent indicators (i.e., LULC changes within 5-km buffer areas around SRs and demographic changes at watershed scale), relevantly reflected the nature and intensity of overall pressures exerted by humans on their environment, and locally on aquatic ecosystems. Recommendations related to the re-greening of peripheral areas around SRs in order to protect water bodies are suggested.

This article discusses the environmental issues facing small hydropower plants (SHPs) operating in temperate lowland rivers of Lithuania. The research subjects are two medium head reservoir type hydro schemes considered within a context of the global fleet of SHPs in the country. This research considers general abiotic indicators (flow, level, water retention time in the reservoirs) of the stream that may affect the aquatic systems. The main idea was to test whether the hydrologic regime has been altered by small hydropower dams. The analysis of changes in abiotic indicators is a complex process, including both pre- and post-reservoir construction and post commissioning of the SHPs under operation. Downstream hydrograph (flow and stage) ramping is also an issue for operating SHPs that can result in temporary rapid changes in flow and consequently negatively impact aquatic resources. This ramping has been quantitatively evaluated. To avoid the risk of excessive flow ramping, the types of turbines available were evaluated and the most suitable types for the natural river flow regime were identified. The results of this study are to allow for new hydro schemes or upgrades to use water resources in a more sustainable way.

Agricultural water management, particularly management of multi-purpose small reservoirs (SRs) in drier savanna areas of the northern Ghana, is being promoted as a key solution to improve agricultural production, enhance food security and livelihoods of smallholder farm households. However, little empirical evidence exist on how effective these small water infrastructures are in terms of delivering multiple benefits and their impact on the livelihood of smallholder farmers. This study assessed the effectiveness and impact of the small reservoirs on smallholder vegetable farmers in northern Ghana. A participatory rating method using a 5-point Likert-scale was used to assess the effectiveness of SRs in delivering multiple livelihood benefits and an endogenous switching regression model was applied to assess the SRs’ impact using a primary data collected from 328 randomly sampled vegetable farmers. Results from the Likert scale analysis show that most of the SRs are either dysfunctional or underutilized and not effective in delivering multiple benefits. Results from the endogenous switching regression model show that there is only about 3% increase in the income of vegetable farmers participating in irrigated vegetable production using SRs against the counterfactual situation but this change is insignificant statistically. The current low level effectiveness and impact of SRs could be enhanced by improving their management, for example, through the provision of incentive mechanisms such as subsidies to the private sector involvement in rehabilitation, management and irrigation service provision and strengthening the capacity of existing water users associations. Furthermore, small reserviors should be recognized not only as water sources for small scale irrigation but also as providers of multiple livelihood benefits to local communities and consequently should attract due attention in public resource allocation in their rehabilitation and management/institutional capacity building. [ABSTRACT FROM AUTHOR]

One hundred and eight species and forms of planktonic organisms have been revealed in three small reservoirs in the Komi Republic (the northeast of European Russia). Species that were not previously known for the water bodies of the Vychegda River Basin (Limnosida frontosa) and the Republic of Komi (Lecane mira, Macrochaetus subquadratus, Filinia longiseta limnetica, and Rhynchotalona falcata) have been found. It has been established that the richness of the planktonic fauna depends on the age of the water body: the maximum number of species is found in the oldest reservoir, namely, the Kazhim Reservoir. The planktonic communities of artificial reservoirs are distinguished by a low level of similarity of faunas both with each other and in comparison with the natural lakes of the region. The fauna distribution in the old reservoirs is uneven. The relatively large fauna richness of planktonic communities in the littoral zones is due to the water-level regime in the reservoirs. [ABSTRACT FROM AUTHOR]

Small reservoirs (SR) are structures that capture and store run-off from upstream catchment area for multiple uses including irrigation, fishing, livestock watering, domestic purpose and groundwater recharge. Though livestock watering is one of the major uses of small reservoirs in the Volta River basin of West Africa, there is limited information on how livestock management practices co-exist with other use of SRs. This study was carried out in a typical Sudano-Sahelian zone within the Volta basin in Burkina Faso, covering five reservoirs to 1) document multiple uses of the reservoirs with a focus on their utilization for livestock production. 2) identify proximate and long-term causes of livestock-related conflicts with regard to multiple uses of the water infrastructure and 3) explore strategies to manage the SR equitably for various uses. Adult males and boys accounted for at least 60% of the users of small reservoirs in our study. Livestock watering was done mainly by adult males. In addition to provision of water for livestock, small reservoirs also contributed to feed resources for animals by providing green forage (pasture grown on residual moisture) in the dry season which accounted for at least 5% of the total dry matter diet of cattle and small ruminant in late dry season. None of the 5 small reservoirs we studied was used for irrigated fodder production. Increased competitions over the use of small reservoirs, damage to irrigated crops by the animals, and increased number of livestock using the small reservoirs were ranked as the most important causes of conflict in the communities. Peaceful co-habitation of the use of the small reservoirs for irrigated vegetable production and livestock watering are essential for reduction of the incidence of conflict. [ABSTRACT FROM AUTHOR]

Whether or not reservoirs contain water throughout the dry season is critical to avoiding late season crop failure in seasonally-arid agricultural landscapes. Locations, volumes, and temporal dynamics, particularly of small (<1 MmX) reservoirs are poorly documented globally, thus making it difficult to identify geographic and intra-annual gaps in reservoir water availability. Yet, small reservoirs are the most vulnerable to drying out and often service the poorest of farmers. Using the transboundary Volta River Basin (∼ 413,000 sq km) in West Africa as a case study, we present a novel method to map reservoirs and quantify the uncertainty of Landsat derived reservoir area estimates, which can be readily applied anywhere in the globe. We applied our method to compare the accuracy of reservoir areas that are derived from the Global SurfaceWater MonthlyWater History (GSW) dataset to those that are derived when surface water is classified on Landsat 8 OLI imagery using the Normalised Difference Water Index (NDWI), Modified NDWI with band 6 (MNDWI1), and Modified NDWI with band 7 (MNDWI2). We quantified how the areal accuracies of reservoir size estimates vary with the water classification method, reservoir properties, and environmental context, and assessed the options and limitations of using uncertain reservoir area estimates to monitor reservoir dynamics in an agricultural context. Results show that reservoir area estimates that are derived from the GSW data are 19% less accurate for our study site than MNDWI1 derived estimates, for a sample of 272 reservoir extents of 0.09 to 72 ha. The accuracy of Landsat-derived estimates improves with reservoir size and perimeter-area ratio, while accuracy may decline as surface vegetation increases. We show that GSW derived reservoir area estimates can provide an upper limit for current reservoir capacity and seasonal dynamics of larger reservoirs. Data gaps and uncertainties make GSW derived reservoir extents unsuitable for monitoring reservoirs that are smaller than 5.1 ha (holding ∼ 49,759 m3), which constitute 674 (56%) reservoirs in the Volta basin, or monitoring seasonal fluctuations of most small reservoirs, limiting its utility for agricultural planning. This study is one of the first to test the utility and limitations of the newly available GSW dataset and provides guidance on the conditions under which this, and other Landsat-based surface water maps, can be reliably used to monitor reservoir resources. [ABSTRACT FROM AUTHOR]

Small reservoirs are characterised by extreme fluctuations in water levels, but how this affects fish communities is not well understood. The aim of the study was to investigate fish communities in two small reservoirs which experience large water level fluctuations over two study years, wet and dry. Six fish species were caught in both reservoirs during the sampling period. The numerically dominant fish species was Enteromius paludinosus in both reservoirs, with Clarias gariepinus contributing the high overall fish biomass. The cyprinids Enteromius lineomaculatus and Enteromius trimaculatus occurred in small numbers, as well as the cichlids Oreochromis mossambicus and Tilapia sparrmanii. Using GLMM, the abundance of both C. gariepinus and E. paludinosus across the two reservoirs was found to be significantly associated with total nitrogen and inorganic nitrogen. C. gariepinus abundances were also associated with water transparency and reactive phosphorus whilst E. paludinosus abundances were associated with ammonia, alkalinity, total dissolved solutes and water depth. E. paludinosus bred mostly during the rainy year. Fish migrations and spawning events were largely triggered by rainfall. Differences between the fish populations in the two reservoirs were small based on fisheries metrics due to the biological attributes of the dominant species, E. paludinosus and C. gariepinus. The shallowness and frequent water level fluctuations in small reservoirs possibly do not allow for specialised habitats to develop, which could lead to high fish species diversity. Their suitability for small-scale fisheries has to be reconsidered as the demand for water for irrigation far outweighs that of the fishery. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a novel framework for small reservoirs extraction in semiarid environment. The task is accomplished through the introduction of a pseudoprobability index derived from multitemporal synthetic aperture radar RGB images. These products are characterized by the ease of interpretation for nonexpert users, and the possibility to be processed using simple algorithms, allowing, in this case, for the definition of an ad hoc band ratio for feature extraction. The reliability of the proposed approach is demonstrated through a case study in Burkina Faso in which 19 reservoirs up to about 6000 m$^2$ extent were tested. The obtained accuracy with respect to the available ground truth is higher than 88%. [ABSTRACT FROM PUBLISHER]

Atmospheric stability conditions over the water surface can affect the evaporative and convective heat fluxes from the water surface. Atmospheric instability occurred 72.5% of the time and resulted in 44.7 and 89.2% increases in the average and maximum estimated evaporation, respectively, when compared to the neutral condition for a small shallow lake (Binaba) in Ghana. The proposed approach is based on the bulk-aerodynamic transfer method and the Monin-Obukhov similarity theory (MOST) using standard meteorological parameters measured over the surrounding land. For water surface temperature, a crucial parameter in heat flux estimation from water surfaces, an applicable method is proposed. This method was used to compute heat fluxes and compare them with observed heat fluxes. The heat flux model was validated using sensible heat fluxes measured with a 3-D sonic anemometer. The results show that an unstable atmospheric condition has a significant effect in enhancing evaporation alongside the sensible heat flux from water surfaces. [ABSTRACT FROM AUTHOR]

The need of water for human use has led the impact on running waters of flow regulation to be of a global-scale. Although the effects of this impact have been widely investigated, efforts have been focused on large dams, so information about small reservoirs and their effects on ecosystem functioning is lacking. A recent collaborative project (IMPARIOS) addressed the effects of flow regulation by small impoundments on leaf-litter decomposition, a key function in low order streams which contributes greatly to the global carbon cycle. Flow regulation was found to affect ecosystem functioning reducing decomposition rate by altering shredders, but the magnitude of change varied among the different sub-climatic regions. The current project examined whether climatic variables modulate the effect of flow regulation on decomposition. For this, 19 bioclimatic variables were studied in relation to the leaf-litter decomposition rate and associated variables (sporulation rate and richness of aquatic hyphomycetes, and richness, density and biomass of total macroinvertebrates and shredders) in 17 streams impacted by regulation structures distributed in four sub-climatic regions within Spain. Overall, decomposition was slower below structures and climate influenced the magnitude of reduction. Effect sizes were negatively related to the seasonal changes in temperature and precipitation and to the general water deficit of the locations. In the future, the forecasted increase of seasonality in precipitation and temperature and the expected increase of number of dams to meet the needs of growing population may exacerbate the effects of flow regulation, altering nutrient recycling and the carbon cycle globally. [ABSTRACT FROM AUTHOR]

During the workshop "Interdisciplinarity around small reservoirs" (at the French Institut de Recherche pour le Développement [IRD], Montpellier, December 2015), twenty researchers from a wide range of academic fields - including hydrology, sociology and agronomy - experienced the development of an interdisciplinary reflexive dialogue. Encouraged to share their research experience on a common object - small reservoirs - the participants explored their different practices and conceptions of interdisciplinarity between natural and social sciences. This exploratory experience highlighted two distinct interdisciplinary postures. The first one emerges from the perception that understanding hydrosystems requires associating multiple scientific approaches to account for the multidimensional water-society relations. Seen as a way to analyse and represent complex objects and systems, the objective of this interdisciplinary posture is to favour linkages and complementarities between academic disciplines. The second posture's objective is rather to explore disciplinary boundaries and identify new research issues by combining and confronting the approaches of multiple researchers. Researchers explore their mutual methodological and conceptual boundaries, draw out the contradictions resulting from their respective approaches and build upon these conclusions to define innovative research questions. While interdisciplinarity is often expressed in the singular form, this workshop invites us to see it as a being plural and built through the multiple practices that nurture interactions between people and disciplines. [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHG) emissions from reservoirs and global urbanization have gained widespread attention, yet the response of GHG emissions to the watershed urbanization is poorly understood. Meanwhile, there are millions of small reservoirs worldwide that receive and accumulate high loads of anthropogenic carbon and nitrogen due to watershed urbanization and can therefore be hotspots of GHG emissions. In this study, we assessed the GHG concentrations and fluxes in sixteen small reservoirs draining urban, agricultural and forested watersheds over a period of one year. The concentrations of p CO 2 , CH 4 and N 2 O in sampled urban reservoirs that received more sewage input were higher than those in agricultural reservoirs, and were 3, 7 and 10 times higher than those in reservoirs draining in forested areas, respectively. Accordingly, urban reservoirs had the highest estimated GHG flux rate. Regression analysis indicated that dissolved total phosphorus, dissolved organic carbon (DOC) and chlorophyll-a ( Chl-a ) had great effect on CO 2 production, while the nitrogen (N) and phosphorus (P) content of surface water were closely related to CH 4 and N 2 O production. Therefore, these parameters can act as good predictors of GHG emissions in urban watersheds. Given the rapid progress of global urbanization, small urban reservoirs play a crucial role in accounting for regional GHG emissions and cannot be ignored. [ABSTRACT FROM AUTHOR]

Resumen. Se evaluó la aptitud del suelo de la región costera del departamento de Córdoba (Colombia), para el cultivo de peces. Se tomaron muestras de suelos, a tres profundidades, en 62 sitios; a las cuales se les midió pH, materia orgánica (MO), fósforo (P), textura e hierro (Fe). Mediante un SIG, los resultados de los parámetros estudiados, las coordenadas de los sitios y la cartografía relacionada se incorporaron en la base de datos del software ArcGIS 9.3 y asociados a las herramientas de análisis espacial para realizar interpolación y generación de mapas temáticos de la aptitud del suelo para piscicultura. Los valores promedio de pH (6,67±0,76), MO (0,51±0,34%) y P (19,62±26,99 ppm) se encontraron dentro del rango para cultivo de peces. La alta concentración de Fe (26,34±22,65 ppm) fue considerada la variable más crítica para la aptitud del suelo para la piscicultura, principalmente en las áreas con pH bajo. El mapa de aptitud del suelo, generado con la integración de las variables estudiadas, permitió identificar 123.625 ha como moderadamente aptas (67,4%), 53.909 ha como aptas (29,3%) y solamente 6.093 fueron consideradas no aptas (3,3%). Sin embargo, este resultado debe ser correlacionado con otras variables como topografía, cobertura vegetal, uso del suelo, disponibilidad hídrica, calidad hídrica, capacidad de drenaje, restricciones ambientales y aspectos socioeconómicos de la región.Abstract. The study was doing to assess the suitability of soil in the coastal region of Cordoba department (Colombia), for fish farming. Soil samples were taken in 62 locations at 20, 70 and 140 cm deep and measured pH, organic matter (OM), phosphorus (P), texture and iron (Fe). Using GIS, results of the studied parameters, coordinates and cartography of related sites were built into the software database of ArcGIS 9.3 and associated to spatial analysis tools for interpolation and generation of thematic maps of soil suitability for fish farming. The average values of the parameters for pH (6.67 ±0.76), MO (0.51 ± 0.34%), P (19.62 ± 26.99 ppm), were within the range to fish farming. The high concentration of Fe (26.34 ± 22.65 ppm) was considered the most critical parameter, especially for areas with low pH. The soil suitability map generated by the integration of the parameters studied, identified 123,625 ha as moderately suitable (67.4%), 53,909 ha were considered suitable (29.3%) and only 6,093 ha were rated unfit (3.3%). However, this result should be correlated with other attributes such as topography, vegetation, land use, water availability, water quality, drainage capacity, environmental constraints and socio-economics of the region.

Burkina Faso is actively pursuing the implementation of Integrated Water Resources Management (IWRM) in its development plans. Several policy and institutional mechanisms have been put in place, including the adoption of a national IWRM action plan (PAGIRE) and the establishment so far of 30 local water management committees (Comités Locaux de l’Eau, or CLE). The stated purpose of the CLE is to take responsibility for managing water at sub-basin level. The two case studies discussed in this paper illustrate gaps between the policy objective of promoting IWRM on the one hand, and the realities associated with its practical on-the-ground implementation on the other. A significant adjustment that occurred in practice is the fact that the two CLE studied have been set up as entities focused on reservoir management, whereas it is envisioned that a CLE would constitute a platform for sub-basin management. This reflects a concern to minimise conflict and optimally manage the country’s primary water resource and illustrates the type of pragmatic actions that have to be taken to make IWRM a reality. It is also observed that the local water management committees have not been able to satisfactorily address questions regarding access to, and allocation of, water, which are crucial for the satisfactory functioning of the reservoirs. Water resources in the reservoirs appear to be controlled by the dominant user. In order to correct this trend, measures to build mutual trust and confidence among water users 'condemned' to work together to manage their common resource are suggested, foremost of which is the need to collect and share reliable data. Awareness of power relationships among water user groups and building on functioning, already existing formal or informal arrangements for water sharing are key determinants for successful implementation of the water reform process underway.

Whether or not reservoirs contain water throughout the dry season is critical to avoiding late season crop failure in seasonally-arid agricultural landscapes. Locations, volumes, and temporal dynamics, particularly of small (

Analisou-se o crescimento dos peixes, a composição das espécies e a produtividade de quatro policultivos (P75, P78, P87 e P207), visando melhorar o manejo e a produtividade pesqueira dos pequenos açudes (0,1-5,0ha) do Semi-Árido brasileiro. Simulou-se as condições desses açudes em viveiros com 120 e 5.000 m² de área, sem renovação de água, utilizando moderada quantidade de adubo e fertilizante. A biomassa inicial variou de 75 a 207kg ha-1, sendo formada por: tilápia do Nilo (Oreochromis niloticus), curimatã pacu (Prochilodus argenteus), carpa comum (Cyprinus carpio), tambaqui (Colossoma macropomum) e tucunaré (Cichla ocellaris). Os peixes apresentaram baixo crescimento (< 0,01g g-1 d-1) após 75 dias de criação (P78 e 87). O crescimento do tambaqui, da tilápia e da curimatã foi reduzido após 53 dias (P75). Em moderada biomassa, o crescimento do tambaqui foi inferior ao da carpa e da curimatã (P207). A produtividade da tilápia atingiu 720 kg ha-1ano-1 (P78), sendo reduzida para 220 kg ha-1ano-1 devido ao processo reprodutivo (P75 e P207). A produtividade da carpa de 1.600 kg ha-1ano-1 foi superior a dos outros peixes (P87). A biomassa inicial de 75 kg ha-1 (60:30:4:3:3% de tilápia, tambaqui, carpa, curimatã e tucunaré, respectivamente) otimizou o crescimento e a produtividade dos peixes. A utilização de tilápias monossexadas e o fornecimento da alimentação suplementar ao tambaqui tornam-se imprescindíveis ao policultivo.The analysed species composition, fish growth, and productivity of four polycultures (P75, P78, P87, and P207) with the objective to improve the small reservoir (0.1-5 ha) fishery management and productivity in the Brazilian semiarid region were conducted a experiment. To mimic reservoir conditions, we used 120 and 5,000m² ponds and evaporation and infiltration water loss was replaced. In addition, manure and fertilizers were used only moderately. The initial biomass of Nile tilapia Oreochromis niloticus, 'tambaqui' Colossoma macropomum, 'curimatã pacu' Prochilodus argenteus, common carp Cyprinus carpio, and 'tucunaré' Cichla ocellaris ranged from 75 to 207kg ha-1. The fish showed low growth rates (

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Reservoir siltation is one of the most important off-site effects of soil erosion. In Burkina Faso a large number of small dams have been built to store rainfall and runoff water in the rainy season, which is much needed for domestic use, irrigation and stock watering in the dry season. This study quantifies the siltation rates of two small reservoirs in southwestern Burkina Faso by comparing the initial and current reservoir bed morphology and by analyzing variations in accumulated sediment in terms of stratigraphical changes and 137Cs concentrations. Results of a bathymetric survey show that both reservoirs have already lost approximately 10% to 15% of their original storage capacity at normal pool level and more than 60% of their initial inactive storage volume at spillway level in the last 15 to 20 years. During this period, inflow sediment had accumulated on the bottom of the reservoir to a thickness of 0.3 m to 0.5 m. Sediment core measurements confirmed this thickness by showing a clear stratigraphical change in core properties with significant variations in the 137Cs concentrations at these specific depths. The thickness of accumulated sediment on top of the relict soil indicates that the reservoirs have a 'half-life' of about 40 to 45 years before siltation might affect its water supply and flood control. Compared with other reservoir studies in West Africa these siltation rates can be seen as reasonable but not alarmingly high. Nevertheless, many of the small dams built during the 1980s are likely to reach their 'half-life' in about 10 to 20 years causing hydrological and geomorphological changes upstream and downstream of the dams. Therefore, further research studies should focus on prevention measures to reduce the off-site effects of erosion and thus to slow down the process of siltation. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]