Hydrologic Flow Regime Research Articles

How economically and environmentally viable are multiple dams in the upper Cauvery Basin, India? A hydro-economic analysis using a landscape-based hydrological model

Abstract. The construction of dams threatens the health of watershed ecosystems. The purpose of this study is to show how multiple dams in a basin can impact hydrological flow regimes and subsequently aquatic ecosystems that depend on river flows. The approach assesses the ecosystem services (ESs), including the tradeoffs between economic and ecological services due to altered flow regimes. It uses a previously developed model that integrates a landscape-based hydrological model with a reservoir operations model on a basin scale. The approach is novel because not only does it offer the analysis of alterations in ecosystem services on a daily scale when pre-dam data are unavailable but also allows for dams to be synthetically placed anywhere in the river network and the corresponding alterations in flow regimes to be simulated in a flexible manner. As a proof of concept, we analyse the economic and ecological performances of different spatial configuration of existing reservoirs instead of synthetically placed reservoirs in the upper Cauvery River basin in India. Such a study is timely and conducted for the first time, especially in light of calls to assess the cascade of reservoirs in India and regions elsewhere where pre-dam data are unavailable. The hydrological impact of different configurations of reservoirs is quantified using indicators of hydrologic alteration (IHAs). Additionally, the production of two major ecosystem services that depend on the flow regime of the river, as indicated by irrigated agricultural production and the normalized fish diversity index (NFDI), is estimated, and a tradeoff curve, i.e. a production possibility frontier, for the two services is established. Through the lens of the indices chosen for the ecosystem services, the results show that smaller reservoirs on lower-order streams are better for the basin economy and the environment than larger reservoirs. Cultivating irrigated crops of higher value can maximize the value of stored water and, with lower storage, generate a better economic value than cultivating lower-value crops while reducing hydrological alterations. The proposed approach, especially when simulating synthetic spatial configurations of reservoirs, can help water and river basin managers to understand the provision of ecosystem services in hydrologically altered basins, optimize dam operations, or even prioritize dam removals with a goal of achieving a balanced provision of ecosystem services.

Impact of LULC changes on hydrological flow regimes and runoff coefficient in Upper Jhelum Basin, India

Impact of LULC changes on hydrological flow regimes and runoff coefficient in Upper Jhelum Basin, India

Climate Change Risks to Freshwater Subsistence Fisheries in Arctic Alaska: Insights and Uncertainty from Broad WhitefishCoregonus nasus

Arctic freshwater ecosystems and fish populations are largely shaped by seasonal and long‐term watershed hydrology. In this paper, we hypothesize how changing air temperature and precipitation will alter freeze and thaw processes, hydrology, and instream habitat to assess potential indirect effects, such as the change to the foraging and behavioral ecology, on Arctic fishes, using Broad WhitefishCoregonus nasusas an indicator species. Climate change is expected to continue to alter hydrologic pathways, flow regimes, and, therefore, habitat suitability, connectivity, and availability for fishes. Warming and lengthening of the growing season will likely increase fish growth rates; however, the exceedance of threshold stream temperatures will likely increase physiological stress and alter life histories. We expect these changes to have mixed effects on Arctic subsistence fishes and fisheries. Management and conservation approaches focused on preserving the processes that create heterogeneity in aquatic habitats, genes, and communities will help maintain the resilience of Broad Whitefish and other important subsistence fisheries. Long‐term effects are uncertain, so filling scientific knowledge gaps, such as identifying important habitats or increasing knowledge of abiotic variables in priority watersheds, is key to understanding and potentially mitigating likely impacts to Arctic fishes in a rapidly changing landscape.

Determining the biogeochemical transformations of organic matter composition in rivers using molecular signatures

Inland waters are hotspots for biogeochemical activity, but the environmental and biological factors that govern the transformation of organic matter (OM) flowing through them are still poorly constrained. Here we evaluate data from a crowdsourced sampling campaign led by the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium to investigate broad continental-scale trends in OM composition compared to localized events that influence biogeochemical transformations. Samples from two different OM compartments, sediments and surface water, were collected from 97 streams throughout the Northern Hemisphere and analyzed to identify differences in biogeochemical processes involved in OM transformations. By using dimensional reduction techniques, we identified that putative biogeochemical transformations and microbial respiration rates vary across sediment and surface water along river continua independent of latitude (18°N−68°N). In contrast, we reveal small- and large-scale patterns in OM composition related to local (sediment vs. water column) and reach (stream order, latitude) characteristics. These patterns lay the foundation to modeling the linkage between ecological processes and biogeochemical signals. We further showed how spatial, physical, and biogeochemical factors influence the reactivity of the two OM pools in local reaches yet find emergent broad-scale patterns between OM concentrations and stream order. OM processing will likely change as hydrologic flow regimes shift and vertical mixing occurs on different spatial and temporal scales. As our planet continues to warm and the timing and magnitude of surface and subsurface flows shift, understanding changes in OM cycling across hydrologic systems is critical, given the unknown broad-scale responses and consequences for riverine OM.

Multiscale Variability of Hydrological Responses in Urbanizing Watershed

Anthropically-induced land-use/land cover (LULC) changes create an imbalance between water and energy fluxes by affecting rainfall-runoff partitioning. This alters the catchment’s flow regime, generating increased highs and reduced low flows, triggering socio-economic and environmental damages. The focus of this study is two-fold (i) to quantify the hydrological changes induced in the urbanizing watershed and (ii) to analyze changes in streamflow variability and generation of extremes (high- and low-flow), using the soil and water assessment tool (SWAT) for Peachtree Creek, USA. The results indicate that the change in LULC significantly influences the availability of soil moisture, ET, and contribution to groundwater flow. It is observed that the variations in these processes regulate the water availability from the surface and sub-surface sources, thus affecting the generation of extreme flows. The spatio-temporal analysis, in response to LULC changes, indicates that (i) urbanization significantly affects baseflow, and its variability depends on the degree of urbanization and the predominant land-use class of the subwatersheds, and (ii) the seasonal variations in the baseflow contribution to the streams depend on ET and the timing and magnitude of groundwater outflow to streams. These variations in ET and groundwater lead to water excess/deficit regions, thus increasing the susceptibility to floods during heavy precipitation events and reducing the reliability of streams during dry periods. Thus, in an urbanizing watershed, the hydrological regime of the watershed may not always be a function of changes in the surface runoff, but will be modified by ET and groundwater dynamics. Further, the study shows that the changes in model parameters can provide insight into the implications of LULC changes on hydrological processes and flow regimes. Evaluating the implications on the basin water balance is paramount for deriving any management operations and restoration activities. The study also outlines the significance of analyzing the spatial and temporal scale streamflow variations for managing water resources to reduce damage to lives and properties.

The Numerical Formulation of Simple Hysteretic Models to Simulate the Large‐Scale Hydrological Impacts of Prairie Depressions

AbstractTopographic depressions have large impacts on the hydrology, ecology, and biogeochemistry in prairie environments. Topographic depressions control the hydrological flow regime through their role in storing water from precipitation and snow melt, and the storage dynamics of topographic depressions affect the retention, transformations, and transport of sediment, carbon, and nutrients. The water stored in topographic depressions supports a diversity of animal and plant species. More generally, depressional wetlands are an integral component of global water, energy, and biogeochemical cycles. In this technical note, we present simple models to simulate hysteretic relationships between storage and contributing area. We consider both spatially distributed and spatially integrated models. The spatially distributed models (the ensemble‐depression model) explicitly simulate storage dynamics for a distribution of discrete depressions. In these spatially distributed models, the large‐scale storage‐contributing fraction relationships are an emergent property of the modeled system. The spatially integrated models (the meta‐depression model) parameterize the large‐scale storage‐discharge relationships. The spatially integrated models are formulated in a way to represent hysteretic behavior. We present a suite of numerical experiments and demonstrate that the ensemble‐depression and meta‐depression models have similar large‐scale behavior. The simple hysteretic models defined here are formulated in a way so that they can easily be incorporated in conventional hydrological models.

Assessment of dam-induced changes in ecogeomorphological behaviour and fluvial functionality in the Damodar River, West Bengal, India

Abstract Anthropogenic interventions in the form of dams and barrages often alter the fluvial functionality and eco-geomorphological (geomorphology, hydrology, and ecology) behaviour of river systems. The present work examines the environmental flow, channel metamorphosis, and fluvial functionality of the Damodar River in the context of Damodar Valley Corporation (DVC) dams and development. Structural (dams, barrages, weirs, etc.) and non-structural (urban–industrial and agricultural disposal with effluents, sand mining, etc.) interventions hinder the ecological functionality of the river. This study portrays that the eco-geomorphological behaviour and fluvial functionality of the river have changed due to flow alteration and diversion by dams and barrages and due to rapid urban–industrial and agricultural growth in the basin area. These changes have affected riverine ecological integrity. The ecological functionality level of this study area ranges from 85 to 181, i.e. from poor to good–fair. The ecological functionality level in the sample channel sections (i.e., the immediate upstream and downstream of the Durgapur Barrage) is poor, and the value ranges from 61 to 100 due to the hydrological impact of the barrage and the Durgapur urban–industrial belt. This assessment work will help to restore the fluvial environment for humans as well as riverine biota. HIGHLIGHTS Dams and barrages have altered the hydrological flow regimes, affecting the eco-geomorphological behaviour of alluvial channels. Dam-induced fluvial metamorphosis is evident in the channel morphological parameters and channel classification. The fluvial functionality index has been applied to evaluate the ecological functionality level for the restoration of the riverine environment.

Evaluation of Gangetic dolphin habitat suitability under hydroclimatic changes using a coupled hydrological-hydrodynamic approach

The aquatic ecosystems are an integral part of the global environment and play a critical role in hydrogeological processes in the rivers. In recent decades, the external stressors on the aquatic species have significantly increased due to hydrologic alterations, human activities, and anthropogenic changes to their natural habitat. Global climate change has led to rivers' hydrological flow regime shifts, leading to unsuitable habitat conditions. It is, therefore, crucial to assess the potential implications of climate change on habitat suitability to ensure the long-term sustainability of freshwater species. In this direction, we investigated the association between endangered Gangetic dolphin populations and climate-driven hydrologic flow regime alterations in the Kulsi river, India. We developed a coupled eco-hydraulic framework comprising hydrological and hydrodynamic modeling to study the impact of past and projected climate change scenarios on the habitat suitability of target species. The framework was tested on a 15-km stretch of the Kulsi River, where the dolphin population has significantly declined in recent years. The temporal changes in the Weighted Usable Area (WUA) were analyzed using flow parameters and habitat suitability curves. Our findings suggest that the dolphin population decline coincided with a decrease in WUA, indicating a strong association between flow regimes and habitat suitability. Under climate change scenarios, multi-model climate projections and hydrological-hydrodynamic simulations show a rising trend in precipitation and streamflow in the basin, with substantial uncertainty. Higher flow depth and velocity would enhance WUA (habitat suitability). Still, the proposed river development projects in upstream regions could pose a serious threat to fragile dolphin communities by changing the seasonal flow patterns. The findings of this study can be included in conservation action plans and flow regulations strategies in upstream projects to ensure the long-term survival of endangered species.

Hydrologic flow regimes in humid tropics river basin.

The study is carried out to understand the impact of the land-use change in terms of alteration in flow regimes, which are understood to be a leading cause of ecological and environmental deterioration in riverine systems. Meenachil river in the humid tropical region of Kerala, India, is one of a kind river with human settlement along the banks for all its 78 kms of flow through the Kottayam District. The analysis of streamflow from four stream gauge stations was done using Range Variability Approach. The analysis was down as a two-time period analysis with the parametric approach with the period separation taken according to prior studies on land-use change. The analysis shows a high degree of alteration, which can be attributed to the land-use change and can be understood as the root cause for the deterioration of water quality and also the ecological distress, which is well documented in the downstream and watershed regions of the river.

Quantifying flow–ecology relationships across flow regime class and ecoregions in South Carolina

The natural flow regime (i.e. magnitude, frequency, duration, timing and rate of change of flow events) is crucial for maintaining freshwater biodiversity and ecosystem services. Protecting instream flow from anthropogenic alterations first requires an understanding of the relationship between aquatic organisms and the flow regime. In this study, we used a unique framework based on random forest modeling to quantify effects of natural flow regime metrics on fish and macroinvertebrate assemblages across ecoregions and flow regime types in the state of South Carolina, USA. We found that all components of the natural flow regime affected both fish and benthic macroinvertebrate assemblages, suggesting that maintaining natural aspects of all flow regime components is critical for protecting freshwater diversity. We identified hydrologic metrics and flow regime components such as magnitude, frequency, and duration of flow events, that were associated with the greatest ecological responses for individual stream classes to help managers prioritize hydrologic and biological metrics of interest during environmental flow standard development. The response of aquatic organisms to hydrologic metrics varied across stream classifications and ecoregions, highlighting the importance of accounting for differences in flow regime and ecoregion when designing environmental flow standards. We provide a flexible framework based on statistical flow-ecology relationships that can be used to inform instream flow management and assess effects of flow alteration on riverine assemblages.

Changing Ecological and Hydrological Conditions in the Himalayan Mountains and Measures of Future Adaptation

The Himalayan mountains are one of the important geographical settings of the planet Earth for the source of global freshwaters. The freshwaters from the Himalayas are life supporting systems of the millions of people residing in downstream Asia. However, the high-altitude mountains of the Himalayas have gone through considerable transformations in hydrology and ecology over the recent past. In the 21st century, the hydrological flow regimes of glacial-fed rivers are threatened by both climate change and human disturbances. Rapidly changing temperature and the frequency, duration and timing of monsoonal precipitation have altered glacier melt, river flow, flood, and downstream volume of water. As a result, the ecosystems and biodiversity as well as irrigation-dependent agriculture in the region is profoundly impacted. The fundamental challenge today is therefore to address the issue of water resources through understanding of hydrological and ecological changes of lake and river systems in the region. Ecohydrology is a sustainability concept, which addresses water resource management through understanding of water cycle, including hydrological processes of rivers and lakes and the structure, and function of ecosystems. Putting ecohydrology at the center of the water resource management program, this mini review discusses rapid ecological and hydrological changes of freshwater systems in the Himalayan mountains and suggested some of the key future adaptation strategies of water resources to rapidly changing regional environment.

Submerged Vegetation Responses to Climate Variation and Altered Hydrology in a Subtropical Estuary: Interpreting 33 Years of Change.

Links between hydrologic modifications, flow and salinity regimes, and submerged aquatic vegetation (SAV) species composition and abundance were assessed with an empirical analysis of 33 years of monitoring data collected at nine sites in Florida's Caloosahatchee River Estuary (CRE). Freshwater inflows to the estuary (30-day means) were often outside the previously recommended envelope of 12.74 to 79.29 m3 s-1. Discharges from Lake Okeechobee through a synthetic hydrologic link were responsible for 43% of the above-envelope flows, but reduced the incidence of below-envelope flows by 30%. A salinity model and salinity stress indices developed for each SAV species indicated that the observed flows generated variable salinity conditions likely to harm both seagrasses and freshwater SAV in the estuary. Regression modeling of SAV abundance generally confirmed the flow and salinity responses expected for each species: Halodule wrightii and Thalassia testudinum in the lower estuary were both harmed by high-flow, low-salinity conditions, while Vallisneria americana in the upper estuary was decimated by low-flow, high-salinity conditions. There was a species-specific effect of the seasonal timing of high flows-T. testudinum was more negatively correlated with high flows in the dry season; H. wrightii in the wet season. The regression analyses also highlighted strong, year-to-year autocorrelations in SAV abundance, indicating reduced resilience after severe losses, particularly for V. americana. Large residual variation in some regression models suggested that factors other than salinity (e.g., optical water quality or grazing impacts) may also influence the system dynamics and should be incorporated in continuing research. This analysis suggests that use of artificial water management infrastructure to reduce extreme high and low flows to the Caloosahatchee and other estuaries could help maintain SAV health in light of intensifying climate variability and degraded watershed flow regulation capacity.

Distinct stores and the routing of water in the deep critical zone of a snow-dominated volcanic catchment

Abstract. This study combines major ion and isotope chemistry, age tracers, fracture density characterizations, and physical hydrology measurements to understand how the structure of the critical zone (CZ) influences its function, including water routing, storage, mean water residence times, and hydrologic response. In a high elevation rhyolitic tuff catchment in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve (VCNP) of northern New Mexico, a periodic precipitation pattern creates different hydrologic flow regimes during spring snowmelt, summer monsoon rain, and fall storms. Hydrometric, geochemical, and isotopic analyses of surface water and groundwater from distinct stores, most notably shallow groundwater that is likely a perched aquifer in consolidated collapse breccia and deeper groundwater in a fractured tuff aquifer system, enabled us to untangle the interactions of these groundwater stores and their contribution to streamflow across 1 complete water year (WY). Despite seasonal differences in groundwater response due to water partitioning, major ion chemistry indicates that deep groundwater from the highly fractured site is more representative of groundwater contributing to streamflow across the entire water year. Additionally, the comparison of streamflow and groundwater hydrographs indicates a hydraulic connection between the fractured welded tuff aquifer system and streamflow, while the shallow aquifer within the collapse breccia deposit does not show this same connection. Furthermore, analysis of age tracers and oxygen (δ18O) and stable hydrogen (δ2H) isotopes of water indicates that groundwater is a mix of modern and older waters recharged from snowmelt, and downhole neutron probe surveys suggest that water moves through the vadose zone both by vertical infiltration and subsurface lateral flow, depending on the lithology. We find that in complex geologic terrain like that of the JRB-CZO, differences in the CZ architecture of two hillslopes within a headwater catchment control water stores and routing through the subsurface and suggest that shallow groundwater does not contribute significantly to streams, while deep fractured aquifer systems contribute most to streamflow.

Development of water and energy Budget-based Rainfall-Runoff-Inundation model (WEB-RRI) and its verification in the Kalu and Mundeni River Basins, Sri Lanka

Distributed Hydrological Models (DHMs) with the capability of simulating catchment-scale water and energy budgets as well as rainfall-runoff-inundation processes are essential tools for Integrated Water Resource Management (IWRM) as well as Water-related Disaster Risk Reduction (WDRR) under changing climate. This research developed a new DHM, the Water and Energy Budget-based Rainfall-Runoff-Inundation (WEB-RRI) model, by integrating the RRI model’s diffusive wave flow equations into a land surface model (hydro-SiB2) to incorporate water and energy budget processes, land-vegetation-atmosphere interactions, soil moisture dynamics, and 2-D lateral water flows to improve interception, evapotranspiration (ET), soil moisture, runoff, and inundation processes. The performance of the new model was assessed using river discharge data, MODIS and GLEAM ET data, and ground as well as satellite inundation extents in the Kalu (wet) and Mundeni (dry) River basins in Sri Lanka. The model was well calibrated and validated (Nash > 0.9) and confirmed to be highly capable of reproducing the long-term (~20 years) observed river discharges (Nash > 0.89) and hydrological flow regime properties for both basins. Particularly, the simulated low flow just before the flood and the peak discharges during the flood, as well as their timings, coincided well with the observed discharges in both basins, which indicates that the model is capable of reproducing soil and vegetation water storages reasonably well, and therefore it can be used for real-time and forecasting applications with the re-starting capability. The model-simulated basin averaged ET fluxes and their trends agreed better with GLEAM (RMSE: ~0.7–0.95 mm/day, correlation: ~0.35–0.39) than with MODIS (RMSE: ~0.96–1.04 mm/day, correlation: ~0.14–0.25). The simulated inundation extents were also consistent with the ground- and MODIS-driven inundation extents. The future focus of this research will be on expanding the model applicability for basin-wide IWRM and WDRR, including flood- and drought-related risk assessments, by employing the model to operational applications (e.g., flood forecasting and seasonal flow prediction) and long-term applications (e.g., catchment responses to past and future climatology, water cycle variability, hydrological extremes, and land-use changes).

The relationship between suspended solids and nutrients with variable hydrologic flow regimes

The hypothesis that “freshwater inflow variability over space and time can drive suspended solids and nutrient concentrations” was tested by comparing three micro-tidal estuaries (Guadalupe, Lavaca-Colorado, and Nueces) in Texas with different hydrologic flow regimes over three years with wet and dry conditions. In all three estuaries, Total suspended solids (TSS) was less than 50 mg/L most of the time. In the Nueces Estuary, TSS of higher than 100 mg/L occurred during frontal events. Dissolved inorganic nitrogen (ammonia+nitrite+nitrate) concentrations were most of the time lowest in the Nueces Estuary (i.e. ≤0.5μmol/L), with low inflow rates and high average salinity of 37.6. Salinity was highest in the river-estuary mouth (average salinity 38.3) of the Nueces Estuary relative to the other oceanic-side stations (average salinity 37), indicating that the system was a “reverse estuary” where evaporation exceeds freshwater inflow, resulting in net inflow of marine water into the estuary. The inverse correlation between ammonium and salinity in all three estuaries and the corresponding negative correlation between nitrite+nitrate concentrations and salinity in the Guadalupe Estuary indicate that the quantity of inflow controls nitrogen concentrations and transformations in the three estuaries. Drought conditions limited riverine transport of nitrogen and sediment to the three estuaries, demonstrating the importance of freshwater inflow to maintaining these constituents. Average silica and orthophosphate concentrations correlated positively with chlorophyll-a in combined data from all three estuaries. Silica and orthophosphate concentrations remained constant over the study period, but correlated with chlorophyll-a when suspended solid was low. Therefore, inflow dynamics drive changes in the salinity regime, suspended solids, and act to maintain nutrient concentrations.

Detecting and quantifying hydromorphology changes in a chilean river after 50 years of dam operation

This study identifies and characterizes hydromorphological changes along the Rapel River downstream of the first large dam built in Chile (1968). A hydromorphological analysis is carried out to assess changes on the hydrological flow regime, bed sediments, and fluvial morphology along a 19 km river reach. Results classify current global hydrological quality as “Moderate” (according to the Indicator for Hydrological Alteration in RIverS, IAHRIS), however specific indicators within this classification scheme identified quality as “Poor”. The morphological quality decreased from “Very Good” to “Good” (assessed by the Morphological Quality Index, MQI). Changes in the planform were particularly intense during the post dam period when intensive lateral mobility occurred, with the corresponding loss of secondary river branches, and with generation of straighter and regular river sections with presence of an armor layer observed along the entire river reach. Between 1991 and 2015 channel stabilization with less lateral mobility was observed, which thought to be associated with the river new equilibrium trend. River width, sinuosity and braiding index changed at different rates along the studied river reach. Our investigation demonstrates that the Rapel River experienced changes differently than those described in the literature given its lower gradient and hydraulic interaction with the Pacific Ocean.

Response to Comments on "Designing river flows to improve food security futures in the Lower Mekong Basin".

Sabo et al presented an empirically derived algorithm defining the socioecological response of the Tonle Sap Dai fishery in the Cambodian Mekong to basin-scale variation in hydrologic flow regime. Williams suggests that the analysis leading to the algorithm is flawed because of the large distance between the gauge used to measure water levels (hydrology) and the site of harvest for the fishery. Halls and Moyle argue that Sabo et al's findings are well known and contend that the algorithm is not a comprehensive assessment of sustainability. We argue that Williams' critique stems from a misunderstanding about our analysis; further clarification of the analysis is provided. We regret not citing more of the work indicated by Halls and Moyle, yet we note that our empirical analysis provides additional new insights into Mekong flow-fishery relationships.

Quantification of Environmental Flow Requirement of the Khun Dan Prakan Chon Dam Using Hydrological-Hydraulic-Habitat Simulation Methods

With increased water demand, reservoir operation has become more complex with the need to quantify the exact amount of water needed for each demand sector. The environmental flow requirement, also known as instream flow is regarded as the first-prioritized objective of the multipurpose water resources projects in Thailand. The capability of reservoirs in Thailand to allocate water for environmental needs depends on available supply, strategies and operating policy. Therefore, this study aims to assess the environmental flow requirements of Khun Dan PrakanChon Dam using three methods; 1) the hydrological method (Tennant, Tessmann, 7Q10, FDC, and VMF), 2) hydraulic method (R2CROSS and wetted perimeter) and 3) habitat simu-lationmethod, using the PHABSIM model for physical habitat simulation of aquatic organisms in the Nakhon Nayok River. The hydrological approach was performed under the historically-naturalized flow data of the NY.1B station and established hydrologic flow regime during low flow and high flow months. The environmental flow rates obtained from two hydraulic methods were based upon field observations at the NY.1B station significantly. However, the biological conditions and interactions of aquatic organisms in the river were not principally characterized in hydrologic and hydraulic approaches. In addition, the estimated results performed by habitat simulation model gave an additional meaning of ecological flow needs mainly for aquatic habitat conservation in the river. By integrating the conditions of hydrologic and hydraulic flow regimes as well as the habitat conservation objectives, environmental flow rates of 8-10 cm were recommended to determine the downstream release of Khun Dan Prakan Chon Dam; these recommendations were very close to those derived using the Tessmann, 7Q10 and PHABSIM methods-Tennant and flow duration curve methods.

Garnierite mineralization from a serpentinite-derived lateritic regolith, Sulawesi Island, Indonesia: Mineralogy, geochemistry and link to hydrologic flow regime

Garnierite represents a significant nickel ore in many lateritic Ni deposits worldwide. To gain a better understanding of its nature and origin, a well-developed garnierite-hosting transect from the Kolonodale area of East Sulawesi, Indonesia, has been investigated using field geology, mineralogy and geochemical data. Garnierite occurs mainly in veins in the lower saprolite of a serpentinite-derived regolith. Mineralogically, it can be determined as an intimate mixture of Ni-rich serpentine-like (lizardite-Népouite) and talc-like (kerolite-pimelite) phases. Results of EMP analyses indicate that Ni is preferentially enriched in the talc-like phases rather than the serpentine-like phases. A sequential precipitation of mineral phases progressively enriched in Ni and Si to form garnierite during weathering is suggested. The Ni-lizardite (2.63–8.49 wt% Ni) with elevated Fe (4.02–6.44 wt%) may have been inherited from saprolite in a first instance and enriched in Ni by cation exchange processes. Newly precipitated minerals are kerolite-pimelite (7.84–23.54 wt% Ni) and then followed by Ni-free quartz. Minor amount of Népouite (23.47–28.51 wt% Ni) occur in laths along shrinkage cracks of previously formed minerals, indicating a late stage paragenetic sequence. With emphasis on a hydrologic consideration, indicators of a preferential flow regime are identified in the garnierite-hosting regolith, including: (i) non-uniform pattern of the garnierite field occurrence, (ii) syn-weathering active nature of the garnierite-hosting structures, (iii) close relationship between the garnierite occurrence and vertical FeMn oxides pipes as well as FeMn oxides patched areas, and (iv) specific physico-chemical property of the garnierite location with higher organic matter concentrations but lower pH values compared to surroundings. It is proposed that the origin of garnierite is closely linked to a preferential flow of oversaturated solutions through accessible conduits in the regolith. Garnierite features as colloidal nature, high organic matter and low pH are key-parameters in metal transport and deposition.

Projected climate change impacts on hydrologic flow regimes in the Great Plains of Kansas

AbstractAlteration of flow regimes due to change in climate and its potential impact on habitat and species has become a major cause of concern for riverine ecosystems. Areas that are more vulnerable to such changes are semiarid river systems or regions experiencing intermittent flow and cyclic droughts. Although ecological changes are expected to occur with flow regime alterations, the biological changes cannot be predicted until the flow in such regions is analysed. This study addresses this concern by providing an analysis of flow for a semiarid river basin in the Central Great Plains from a 50 and 100‐year projection climate data. The projected data for these two periods are then compared with 30‐year historical data to determine changes in flow. Five major components of flow regime, magnitude, duration, and timing of annual extreme water conditions, frequency and duration of high and low pulses, and rate and frequency of water condition changes, were examined with respect to climate change for their impact on the ecology of the basin. This analysis strongly suggests that inter‐ and intra‐annual changes in flow regimes will result in the intensified drying of the basin represented by the increased number of low flow periods followed by higher occurrences of high flow events of shorter duration with expected changes in climate.