Regional Flow Regime Research Articles

Estimation of instantaneous peak flows in Canadian rivers: an evaluation of conventional, nonlinear regression, and machine learning methods.

Instantaneous peak flows (IPFs) are often required to derive design values for sizing various hydraulic structures, such as culverts, bridges, and small dams/levees, in addition to informing several water resources management-related activities. Compared to mean daily flows (MDFs), which represent averaged flows over a period of 24 h, information on IPFs is often missing or unavailable in instrumental records. In this study, conventional methods for estimating IPFs from MDFs are evaluated and new methods based on the nonlinear regression framework and machine learning architectures are proposed and evaluated using streamflow records from all Canadian hydrometric stations with natural and regulated flow regimes. Based on a robust model selection criterion, it was found that multiple methods are suitable for estimating IPFs from MDFs, which precludes the idea of a single universal method. The performance of machine learning-based methods was also found reasonable compared to conventional and regression-based methods. To build on the strengths of individual methods, the fusion modeling concept from the machine learning area was invoked to synthesize outputs of multiple methods. The study findings are expected to be useful to the climate change adaptation community, which currently heavily relies on MDFs simulated by hydrologic models.

The changing nature of groundwater in the global water cycle.

In recent decades, climate change and other anthropogenic activities have substantially affected groundwater systems worldwide. These impacts include changes in groundwater recharge, discharge, flow, storage, and distribution. Climate-induced shifts are evident in altered recharge rates, greater groundwater contribution to streamflow in glacierized catchments, and enhanced groundwater flow in permafrost areas. Direct anthropogenic changes include groundwater withdrawal and injection, regional flow regime modification, water table and storage alterations, and redistribution of embedded groundwater in foods globally. Notably, groundwater extraction contributes to sea level rise, increasing the risk of groundwater inundation in coastal areas. The role of groundwater in the global water cycle is becoming more dynamic and complex. Quantifying these changes is essential to ensure sustainable supply of fresh groundwater resources for people and ecosystems.

Collateral benefits: River flow normalization for endangered fish enabled riparian rejuvenation

AbstractLike most rivers worldwide, the transboundary North American Kootenay/i River has experienced multiple impacts including watershed developments, river channelization, and floodplain clearing, draining, and diking. Construction of Libby Dam was authorized by the 1964 Columbia River Treaty (CRT) between the United States and Canada, and in 1975 began regulating downstream flows for flood risk management and hydropower generation. Following cumulative impacts, the endemic Kootenai River White Sturgeon population collapsed and was designated as endangered in 1994 (U.S. Endangered Species Act). Subsequent Biological Opinions from the U.S. Fish and Wildlife Service prescribed Libby Dam operations to provide springtime flow pulses for sturgeon spawning. These provided the unanticipated benefit of substantial seedling recruitment of native and introduced riparian cottonwoods and willows. The regulated flow regime was further adaptively managed to provide a more normative (natural) regime, to balance ecological functions with flood risk management and hydropower generation. The broadened ecological considerations would be consistent with the proposed priorities for the modernization of the international CRT. The observed responses revealed that (1) diverse aquatic and riparian organisms are dependent on common river flow characteristics; (2) a normalized flow regime provided substantial ecological benefits; and (3) due to multiple influences, hybrid ecosystems develop along regulated rivers, with a blending of natural and altered processes and communities. For other regulated rivers, we recommend that (1) high springtime flows be allowed, as feasible; (2) followed by the gradual post‐peak recession; and (3) the maintenance of sufficient flows through the warm and dry interval of mid to late summer.

Macroscale controls determine the recovery of river ecosystem productivity following flood disturbances

River ecosystem function depends on flow regimes that are increasingly modified by changes in climate, land use, water extraction, and flow regulation. Given the wide range of variation in flow regime modifications and autotrophic communities in rivers, it has been challenging to predict which rivers will be more resilient to flow disturbances. To better understand how river productivity is disturbed by and recovers from high-flow disturbance events, we used a continental-scale dataset of daily gross primary production time series from 143 rivers to estimate growth of autotrophic biomass and ecologically relevant flow disturbance thresholds using a modified population model. We compared biomass recovery rates across hydroclimatic gradients and catchment characteristics to evaluate macroscale controls on ecosystem recovery. Estimated biomass accrual (i.e., recovery) was fastest in wider rivers with less regulated flow regimes and more frequent instances of biomass removal during high flows. Although disturbance flow thresholds routinely fell below the estimated bankfull flood (i.e., the 2-y flood), a direct comparison of disturbance flows estimated by our biomass model and a geomorphic model revealed that biomass disturbance thresholds were usually greater than bed disturbance thresholds. We suggest that primary producers in rivers vary widely in their capacity to recover following flow disturbances, and multiple, interacting macroscale factors control productivity recovery rates, although river width had the strongest overall effect. Biomass disturbance flow thresholds varied as a function of geomorphology, highlighting the need for data such as bed slope and grain size to predict how river ecosystems will respond to changing flow regimes.

The role of water management and river morphology on stranding pool formation

Fish can be stranded in pools during flow recessions that may occur naturally or as a result of dam operations. Past studies have recommended dam operation guidelines that only consider water surface elevation (WSE) recession rate to reduce fish stranding potential. Here, we holistically consider the role of flow, WSE recession rate, and river-floodplain topography under unregulated and regulated flow regimes to predict the potential of stranding pool formation. The proposed methodology leverages advances in two-dimensional (2D) surface hydraulic (HD) modeling and high-resolution topobathymetric LiDAR surveys. We applied this method to the South Fork Boise River (SFBR), Idaho, USA. We developed a 2D HD model supported by meter-resolution topobathymetric data to simulate channel and floodplain hydraulics and stranding pool formation for different flow scenarios.Comparison between modeled and fieldsurveyed stranding pool locations shows good match, supporting the use of this method to predict stranding pool potential. Results show that potential for stranding pool formation (number of pools and their surface area) increases with flow for the same flow recession rate. Contrary to expectations, our model predicts that unregulated flows have a considerably higher number of potential fish stranding pools than for regulated flows in the SFBR. The reach-average WSE recession rates were higher for unregulated (0.07 to 0.09 cm/h) than for regulated (0.02 to 0.04 cm/h) flow based on daily mean flows. Our study has shown the importance of river and floodplain morphology and hydraulics to predict fish stranding pool locations and analyze impacts of flow regulations on fish stranding. This approach may provide helpful information to identify potential fish stranding pools and mitigation and to manage for fish stranding issues in regulated and unregulated river systems.

Exploring functional flow heterogeneity in regulated flow regime: Fish species turnover along hydraulic gradients in an artificial waterway network

AbstractHumans have altered river flows leading to a loss of connection with floodplain habitats. The expansion of agriculture in floodplains has resulted in landscapes dominated by irrigated farmland. A key challenge in water management is to conserve existing ecological communities and habitat heterogeneity, while simultaneously maintaining engineered infrastructure for agriculture. In this study, we focused on an artificial channel network for irrigation with a regulated flow regime and its function as habitat for various fish species. Differences in hydraulic conditions among channels and compositional changes in fish species were examined to clarify functional flow heterogeneity. Analyzed using pairwise Simpson dissimilarity among sampling reaches, species turnover was positively associated with Froude number (flow intensity) differences at intermediate discharges, and with differences in cross‐sectional areas (flow magnitude) at low discharges. Drastic changes in inflows should be considered for the effective conservation of flow heterogeneity, even under a regulated flow regime. Improved engineering design to manage the hydraulic environment is one option for maintaining the ecological value of lateral waterbodies in human‐dominated landscapes. Our findings provide insights into the importance of functional flow heterogeneity to conserve fish species diversity.

Assessment of ecological state of serially impounded Himalayan River using diatoms-based matrices: Identification of critical stretches for management

The ecological state of the serially impounded Himalayan river Bhagirathi is assessed using benthic diatom-based matrices. Six stations (S1-S6) located in stretches receiving constant low flow (S2, S4,S5) and regulated flow regimes (S3, S6) along the continuum were sampled for the diatom community at monthly intervals from October 2016 to September 2017. The samples were processed and identified according to standard literature. The van Dam ecologic values revealed identical prevailing condition based on their percent abundance, reflecting the existing state of riverine ecosystem. Compared to S1 (located upstream in natural flow) the percent share of the dominant category tolerant-N-autotroph for nitrogen-uptake; polyoxybiontic (100% O2 saturation) for oxygen requirement; and β-mesosprobe (BOD 2–4 mg l−1) for saprobity valuesshow decline in the modified stretches except for S6 and being serious at S3 followed by S2, S4 and S5. On the contrary, obligatory-N-heterotrophs (taxa needing continuously elevated organically bounded nitrogen), low to moderate oxygen saturation (30–70%), and α-meso-poly saprobous (biological oxygen demand 8–12 mg l−1) appeared in these modified stretches. The eutrophic (high level of nutrients) and hypereutrophic (nutrient rich water characterised by algal blooms) catagories occurred at S2, S3 and S4, reflecting enhanced organic load, which is further demonstrated by water quality indices. Some tolerant taxa (Nitzschia palea, Nitzschia paleacae) contributed a considerable share in the flow modified stretches and hence are considered taxa of concern for future studies as they are rarely reported from Himalayan rivers. The anomalies in ecological state confirm deterioration and hence the sections along the modified stations are called critical stretches, S3 followed by S2 and S4 being the most stressed and recommended for proper management. The study also affirms the applicability of diatom-based matrices for Hydroelectric project (HEP) impact assessment in the Himalayan rivers.

Groundwater flow reversal between small water bodies and their adjoining aquifers: A numerical experiment

AbstractThe countless kettle holes in the Late Pleistocene landscapes of Northern Europe are hotspots for biodiversity and biogeochemical processes. As a rule, they are hydraulically connected to the shallow groundwater system. The rapid, intensive turnover of carbon, nutrients and pollutants in the kettle holes therefore has a major impact on the quality of the shallow groundwater downstream. As a result of high‐evapotranspiration rates from their riparian vegetation or strong storm events, the process of downstream groundwater flow may stagnate and reverse back towards the kettle hole, making interactions between the groundwater and kettle hole more complex. Furthermore, the highly heterogeneous soil landscape in the catchment contributes to this complexity. Therefore, the present study aims to enhance our understanding of this complicated interaction. To this end, 24 model variants were integrated into HydroGeoSphere, capturing a wide range of uncertainties in quantifying the extent and timing of groundwater flow reversal between a kettle hole and the adjacent aquifer. The findings revealed that the groundwater flow reversal lasted between 1 month and 19 years at most and occurred in a distance of more than 140 m downstream of the kettle hole. Our results demonstrated that the groundwater flow reversal arises especially often in areas where the shallow aquifer possesses low‐hydraulic conductivity. There may also be a recurrent circulating flow between the groundwater and kettle hole, resulting in solute turnover within the kettle hole. This holds particularly true in dry periods with medium to low‐water levels within the kettle hole and a negative water balance. However, shallow groundwater flow reversals are not necessarily a consequence of seasonal effects. In this respect, the properties of the local shallow aquifer by far outweigh the effect of the kettle hole location in the regional flow regime.

Assessing the occurrence of egg stranding for trout and salmon in a regulated river

AbstractA key challenge in many regulated rivers is to define adequate flow levels to protect aquatic organisms. Provisioning of suitable flow can be pivotal bottlenecks for fishes such as salmon and trout that use the riverbed as an incubation habitat. Additionally, the locations where females spawn will define the probability that embryos will be dewatered during the incubation period in a regulated flow regime. We investigated the water flow, dewatering, and incubation mortality in Atlantic salmon and brown trout in natural nests over 19 years in the regulated Bjoreio River in western Norway. During the study period, different flow strategies were applied to mitigate the dewatering of incubating salmon and trout embryos. Average survival in nests sampled in late winter ranged from 54% to 92% among years and was significantly correlated with the minimum water flow occurring during the incubation period. Mortality was significantly higher in nests in shallow areas, reflecting nests exposed to dewatering. The results demonstrate a strong link between incubation mortality and managed flow regimes for river spawning salmonids. Using detailed information on the nest location and incubation mortality, we estimate minimum flow requirements for this river and demonstrate an approach to effectively mitigate the impact of river regulations on embryo survival in Atlantic salmon and brown trout.

Особенности условий среды обитания, режима рыболовства и состояния популяции налима Lota lota L. в озерах-водохранилищах бассейна Белого моря (Республика Карелия)

The fishery water fund of the North and North-West of the European part of Russia is characterized by a high specific gravity of water bodies with a regulated flow regime. Recently, some reservoir lakes in the region have been decreasing their fishery importance. The Vygozero (Vygozersko-Ondskoe) and the Topo-Pyaozero (Kumskoe) reservoirs located in the Republic of Karelia and belonging to the White Sea basin which differ in some limnological parameters have been chosen as model lakes-reservoirs. The results of the research works carried out as part of forecasting themes and economic and contractual tasks (SevNIORKh, NFRI PetrSU, NWPI KarRC RAS, KarelNIRO) are presented. The actual industrial facilities and types of economic activities in the Vygozero and the Topo-Pyaozero reservoirs have already affected and continue to exert their negative impact on fish stocks. The greatest damage to fish resources including burbot is done in terms of reproduction due to the anomalous level regime, water discharge, erosion of shallows, irrational fishing, hydro-construction, hydropower, pollution of the aquatic environment and soils with industrial wastes, etc. The main biological and structural-population indicators of burbot in the reservoirs have been studied. The analysis of its abundance and biomass at the present stage that are necessary for the rational regulation of the fishery have been carried out. Calculating the burbot stock abundance based on materials of 2000-2020 will allow to recommend the volume of the total allowable catch for the Topo-Pyaozero (Kumskoe) Reservoir - 37 tons (21% of the commercial reserve) and for the Vygozero (Vygozersko-Ondskoe) Reservoir - 20 tons (25% of the commercial reserves), which is within the seizure rate (20-27%). The intensity of fishing and increasing catches of burbot in these reservoirs should be considered as mandatory measures in terms of biological reclamation in the reservoirs.

Flow regime changes in the Lancang River, revealed by integrated modeling with multiple Earth observation datasets

The flow regime change of rivers, especially transboundary rivers, affected by reservoir regulations is evident worldwide and has received much attention. Investigating dam-induced flow regime alterations is essential for understanding potential adverse downstream effects and facilitating dialogue around coordinated water use in transboundary basins, such as the Lancang River Basin (LRB). This study explored the value of combining several types of satellite Earth observation (EO) datasets that monitor different water balance components to constrain the parameter space of lumped conceptual hydrological models. Thus, we aimed to reconstruct the natural flow regimes upstream and downstream of the cascade reservoirs. Specifically, reservoir water storage changes were first estimated using satellite imagery and altimetry datasets. Then, storage changes were combined with hydrological model simulations of reservoir inflow to estimate the regulated flow regime downstream. Our results showed that integrated hydrological modeling combined with EO datasets exhibited better overall performance. Continuous warming and drying of the LRB resulted in a decrease in discharge of approximately 47 %. By comparing the simulated natural and regulated flow regimes, we revealed the pivotal role of the Xiaowan and Nuozhadu reservoirs in regulating natural flows. The wet season shortens (approximately 45 days), the flood peak flattens, and the low flow in the dry season has primarily increases. The two reservoirs attenuated 50 % of the flood peaks in the wet seasons and mitigated droughts by releasing up to 100 % of the natural flows in the dry seasons at the China–Laos border. Overall, these results enhance the understanding of upper reservoir operation, and the approaches can be applied to studies of dammed basins under climate change scenarios when knowledge of the upstream area is limited.

Impeding access to tributary spawning habitat and releasing experimental fall-timed floods increase brown trout immigration into a dam’s tailwater

River ecosystems have been altered by flow regulation and species introductions. Regulated flow regimes often include releases designed to benefit certain species or restore ecosystem processes, and invasive species suppression programs may include efforts to restrict access to spawning habitat. The impacts of these management interventions are often uncertain. Here, we assess hypotheses regarding introduced brown trout ( Salmo trutta) movement in a regulated river. We model mark–recapture data in a multistate framework to assess whether movement was affected by the operation of a tributary weir (restricting access to spawning habitat), experimental releases of fall-timed high flow experiments (Fall HFEs), or simply increased during the fall, spawning season. Our results suggest that the presence of the weir led to reduced tributary homing and the release of Fall HFEs stimulated upstream movement and straying. Both effects are of a similar magnitude, however the Fall HFE effect is more certain. Our results suggest the expansion of an invasive species was stimulated by management interventions, and demonstrate the potential for unanticipated outcomes of restoration in highly altered river ecosystems.

Low flows in a regulated river system are associated with reduced breeding bird abundance and diversity in Yosemite National Park, California

AbstractRiver regulation can alter the magnitude, frequency, duration, and timing of flows, which influences the function of downstream ecosystems. Bird communities can be useful indicators of ecosystem function as individual species respond to varied changes in habitat structure and food availability. We examined the relative importance of different aspects of a regulated flow regime (average daily flow, the number of days flows fell below the 25th percentile, the timing and magnitude of maximum flows, and the inter‐annual duration of flows below the historical median) on predicted bird abundance and diversity using 11 years of data collected within a floodplain meadow system located downstream of Hetch Hetchy Reservoir in Yosemite National Park, California. We found that prolonged periods of low flows were negatively associated with the number of breeding birds detected, as well as the species richness of the breeding bird community. Species richness was also negatively correlated with delays in spring runoff delivery. We opportunistically looked at the same hydrologic variables in a parallel unregulated system, the Merced River through Yosemite Valley, and did not find the same strong relationship with bird community data. This suggests that the dam may be exacerbating the effects of drought.

Experimental reductions in subdaily flow fluctuations increased gross primary productivity for 425 river kilometers downstream.

Aquatic primary production is the foundation of many river food webs. Dams change the physical template of rivers, often driving food webs toward greater reliance on aquatic primary production. Nonetheless, the effects of regulated flow regimes on primary production are poorly understood. Load following is a common dam flow management strategy that involves subdaily changes in water releases proportional to fluctuations in electrical power demand. This flow regime causes an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production. In collaboration with dam operators, we designed an experimental flow regime whose goal was to mitigate negative effects of load following on ecosystem processes. The experimental flow contrasted steady-low flows on weekends with load following flows on weekdays. Here, we quantify the effect of this experimental flow on springtime gross primary production (GPP) 90-to-425km downstream of Glen Canyon Dam on the Colorado River, AZ, USA. GPP during steady-low flows was 41% higher than during load following flows, mostly owing to nonlinear reductions in sediment-driven turbidity. The experimental flow increased weekly GPP even after controlling for variation in weekly mean discharge, demonstrating a negative effect of load following on GPP. We estimate that this environmental flow increased springtime carbon fixation by 0.27g C m-2 d-1, which is ecologically meaningful considering median C fixation in 356US rivers of 0.44g C m-2 d-1 and the fact that native fish populations in this river are food-limited.

Hydrogeomorphic Scaling and Ecohydraulics for Designing Rescaled Channel and Floodplain Geometry in Regulated Gravel–Cobble Bed Rivers for Pacific Salmon Habitat

Societies are increasingly restoring and/or rehabilitating rivers below dams for keystone species such as salmon. A fundamental concept for rehabilitating river morphology below dams for salmon is that a rescaled version of the river corridor synchronized to the regulated flow regime can restore habitat quantity and quality. Downscaled and resized hydrographs have been shown to provide environmental benefits to fish communities including salmon as well as riparian vegetation communities. However, less research exists on how this can be achieved through the topographic rescaling of heavily modified and regulated river corridors. The goal of this paper is to review analytical methods to determine initial of size of rescaled channel and floodplain mesohabitat units in regulated gravel–cobble bed rivers for Pacific salmon (Oncorhynchus spp.) habitat using hydrogeomorphic scaling and ecohydraulics. Hydrogeomorphic flow scaling is the prediction of river morphology and geometry using empirical and analytical relationships. Ecohydraulic scaling refers to the use of ecohydrology, habitat suitability curves, and fish density relationships to determine the size of mesohabitat units for ecologically relevant flows. In practice, these are complimentary first order estimates of channel and floodplain configurations followed by iterative design in a hierarchical manner. This review advances the science of river design by synthesizing these complimentary ideologies for Pacific salmon habitat restoration in regulated rivers. Following the review, the layout of features is briefly discussed followed by a discussion of important considerations beyond the physical and topographic rescaling of river corridors for salmonid habitat restoration.

River ecosystem endangerment from climate change-driven regulated flow regimes

Major threats of freshwater systems are river damming and habitat degradation, further amplified by climate change, another major driver of biodiversity loss. This study aims to understand the effects of climate change, and its repercussions on hydropower production, on the instream biota of a regulated river. Particularly, it aims to ascertain how mesohabitat availability downstream of hydropower plants changes due to modified flow regimes driven by climate change; how mesohabitat changes will influence the instream biota; and if instream biota changes will be similar within and between biological groups. We used a mesohabitat-level ecohydraulic approach with four biological elements – macrophytes, macroalgae, diatoms and macroinvertebrates – to encompass a holistic ecosystem perspective of the river system. The ecological preferences of the biological groups for specific mesohabitats were established by field survey. The mesohabitat availability in three expected climate change-driven flow regime scenarios was determined by hydrodynamic modeling. The biota abundance/cover was computed for the mesohabitat indicator species of each biological group. Results show that climate-changed flow regimes are characterized by a significant water shortage during summer months already for 2050. Accordingly, the regulated rivers' hydraulics are expected to change towards more homogeneous flow conditions where run habitats should prevail. As a result, the biological elements are expected to face abundance/cover modifications ranging from decreases of 76% up to 67% increase, depending on the biological element and indicator taxa. Diatoms seem to endure the greatest range of modifications while macrophytes the slightest (15% decrease to 38% increase). The greatest modifications would occur on decreasing abundance/cover responses. Such underlies an important risk to fluvial biodiversity in the future, indicting climate change as a significant threat to the fluvial system in regulated rivers.

Climatic signatures in regulated flow regimes across the Central and Eastern United States

Study region: 42 catchments distributed throughout Central and Eastern U.S. Study focus: Enhanced hydroclimatic variability threatens human water uses, and there is an urgent need to quantify projected alterations of flow regimes. This issue has been largely addressed in unregulated rivers through the development of similarity frameworks relating climate properties with the hydrologic response of catchments. However, the impact of damming on climate signatures of river flow regimes is largely unexplored. To fill this gap, this study investigates unregulated streamflows of a selection of sites using a climate-based similarity framework. Then, the corresponding regulated regimes are analyzed to understand how the obtained regime classification is affected by regulation. New hydrological insights for the region: Our results reveal that flood control dams retain but dampen climate signatures of flow regimes, reducing the regional heterogeneity of downstream hydrographs. Conversely, in the study area, urban water supply structures promote climate-independence of river regimes and tend to break the link between climate and river flows, thereby promoting the spatial diversification of the hydrologic response. The observed impact of each specific water use is explained based on quantitative indexes that relates to the regulation capacity of reservoirs and their degree of exploitation. Overall, climatic signatures are still detectable in most regulated streamflows, though climatic control on river regimes is largely concealed by the profound hydrological alterations induced by dams.

Review: origin, heating process, and groundwater flow system of non-volcanic thermal aquifers in Tunisia

Thermal groundwater is of great economic and social importance. Tunisia is characterized by its hot groundwater spread over several regions. Hydrothermal resources need further investigation and diagnosis to determine their local, Mediterranean, or regional thermal sources and flow regimes. This study aims to differentiate origin and heating process of non-volcanic thermal aquifers. For this, three thermal provinces in Tunisia were reviewed and studied: Cap Bon thermal province (Korbous), Fluorinated Province of Zaghouan (Zriba Hammam), and Southern thermal province (El Hamma). A multidisciplinary approach, integrated with hydrogeological, geochemical, and isotopic data from the various studied provinces, was used. Results reveal that the studied thermal waters are of meteoric origin heated by deep circulation and acquire their thermal energy from the Earth’s heat during long-time residence. The thermal waters of El Hamma are the oldest and the northern waters are younger, influenced by the recent recharge. Thermal groundwater chemistry is influenced by minerals related to rock-water interaction. This study confirms that thermal waters, in non-volcanic areas, are of meteoric origin; their temperature and salinity depend on the residence time and their depth of circulation. This makes it possible to rationalize for their use in the appropriate sectors and ensure sustainable management.

Modeling groundwater flow under chaotic urbanization constraints in Kinshasa Capital Region (D.R. Congo)

Groundwater is used as an alternative source of drinking water in the chaotically urbanized African mega city of Kinshasa (DR Congo). However, groundwater abstraction without proper management leads to aquifers mining. The main objective of this study was to better understand the regional groundwater flow regime and to build a groundwater management tool for an area of 2187.36 km2 using Visual MODFLOW Flex. The model's input data were collected from various databases of national agencies and companies in charge of water engineering and management. Large scale steady-state and transient regional model was set up for the period 2000–2014, calibrated and validated to optimize groundwater development scenarios. The recharge in the area is estimated at an average of 236.21 mm/yr and is high in the southwest and less in paved areas and sandy-clayey soils in the east. The calibrated model had Nash-Sutcliffe Efficiency (NSE) coefficient of 0.9 and correlation coefficient of 0.98 and 0.96 for the steady-state and transient state, respectively. The accuracy of the calculated ground water levels was also judged by standard error of estimation which was 0.24 m and root mean squared of 16.8 m. The results for the three (3) scenarios from the baseline, which comprised increasing pumping rates by 10, 25 and 50%, indicated a further decrease in groundwater levels by 0.05m, 0.076m and 0.12 m, respectively. The modeled groundwater flow indicated that the flow direction for the whole study area is mainly from highlands towards lowlands, heading north, where the Congo River is located.

Classification and Prediction of Natural Streamflow Regimes in Arid Regions of the USA

Understanding how natural variation in flow regimes influences stream ecosystem structure and function is critical to the development of effective stream management policies. Spatial variation in flow regimes among streams is reasonably well understood for streams in mesic regions, but a more robust characterization of flow regimes in arid regions is needed, especially to support biological monitoring and assessment programs. In this paper, we used long-term (41 years) records of mean daily streamflow from 287 stream reaches in the arid and semi-arid western USA to develop and compare several alternative flow-regime classifications. We also evaluated how accurately we could predict the flow-regime classes of ungauged reaches. Over the 41-year record examined (water years 1972–2013), the gauged reaches varied continuously from always having flow > zero to seldom having flow. We predicted ephemeral and perennial reaches with less error than reaches with an intermediate number of zero-flow days or years. We illustrate application of our approach by predicting the flow-regime classes at ungauged reaches in Arizona, USA. Maps based on these predictions were generally consistent with qualitative expectations of how flow regimes vary spatially across Arizona. These results represent a promising step toward more effective assessment and management of streams in arid regions.