Estimating the uncertainty in simulating the impacts of small farm dams on streamflow regimes in South Africa

Abstract

Small dams represent an important local-scale resource designed to increase water supply reliability in many parts of the world where hydrological variability is high. There is evidence that the number of farm dams has increased substantially over the last few decades. These developments can have a substantial impact on downstream flow volumes and patterns, water use and ecological functioning. The study reports on the application of a hydrological modelling approach to investigate the uncertainty associated with simulating the impacts of farm dams in several South African catchments. The focus of the study is on sensitivity analysis and the limitations of the data that would be typically available for water resources assessments. The uncertainty mainly arises from the methods and information that are available to estimate the dam properties and the water use from the dams. The impacts are not only related to the number and size of dams, but also the extent to which they are used for water supply as well as the nature of the climate and the natural hydrological regimes. The biggest source of uncertainty in South Africa appears to be associated with a lack of reliable information on volumes and patterns of water abstraction from the dams.

Citation Hughes, D. A. & Mantel, S. K. (2010) Estimating the uncertainty in simulating the impacts of small farm dams on streamflow regimes in South Africa. Hydrol. Sci. J. 55(4), 578–592.     

Assessing the effect of climate natural variability in water resources evaluation impacted by climate change

Water resource assessment on climate change is crucial in water resource planning and management. This issue is becoming more urgent with climate change intensifying. In the current research of climate change impact, climate natural variability (fluctuation) has seldom been studied separately. Many studies keep attributing all changes (e.g. runoff) to climate change, which may lead to wrong understanding of climate change impact assessment. Because of lack of long enough historical series, impacts of climate variability have been always avoided deliberately. Based on Latin hypercube sampling technique, a block sampling approach was proposed for climate variability simulation in this study. The widely used time horizon (1961–1991) was defined as baseline period, and the runoff variation probability affected by climate natural variability was analysed. Allowing for seven future climate projections in total of three GCMs (CSIRO, NCAR, and MPI) and three emission scenarios (A1B, A2, and B1), the impact of future climate change on water resources was estimated in terms of separating the contribution from climate natural variability. Based on the analysis of baseline period, for the future period from 2021 to 2051, the impact of climate natural variability may play a major part, whereas for the period from 2061 to 2091, climate change attributed to greenhouse gases may dominate the changing process. The results show that changes from climate variability possess a comparable magnitude, which highlights the importance to separate impacts of climate variability in assessing climate change, instead of attributing all changes to climate change solely. Copyright © 2012 John Wiley & Sons, Ltd.     

Towards Quantifying the Likelihood of Water Resource Impacts from Unconventional Gas Development

Gas production from unconventional reservoirs has led to widespread environmental concerns. Despite several excellent reviews of various potential impacts to water resources from unconventional gas production, no study has systematically and quantitatively assessed the potential for these impacts to occur. We use empirical evidence and numerical and analytical models to quantify the likelihood of surface water and groundwater contamination, and shallow aquifer depletion from unconventional gas developments. These likelihoods are not intended to be exact. They provide a starting point for comparing the probabilities of adverse impacts between types of water resources and pathways. This analysis provides much needed insight into what are “probable” rather than simply “possible” impacts. The results suggest that the most likely water resource impacts are surface water and groundwater contamination from spills at the well pad, which can be as high as 1 in 10 and 1 in 100 for each gas well, respectively. For wells that are hydraulically fractured, the likelihood of contamination due to inter-aquifer leakage is 1 in 10⁶ or lower (dependent on the separation distance between the production formation and the aquifer). For gas-bearing formations that were initially over-pressurized, the potential for contamination from inter-aquifer leakage after production ceases could be as high as 1 in 400 where the separation between gas formation and shallow aquifer is 500 m, but will be much lower for greater separation distances (more characteristic of shale gas).     

Design and analysis of the Sydney deepwater ocean outfall environmental monitoring programme: a critique

The Sydney Environmental Monitoring Programme (EMP) measured the environmental performance of Sydney's new deepwater sewage outfalls against a wide range of criteria related to impacts on marine ecosystems and on human use of marine resources. It consisted of a number of interacting studies conducted during the period 1989 to 1993. Given that all the studies have now been finalized and the data analysed and presented (see papers in this volume), it is appropriate to review the program as a whole and identify, with the benefit of hindsight, where things could have been done better. This paper focuses mainly on the experimental design and statistical treatment of the studies conducted, although management problems are also briefly addressed. Overall it is concluded that the studies making up the EMP contributed greatly to enhancing our understanding of the marine environment of the coastal shelf off Sydney, an area which had previously received only limited attention. Most of the studies, however, suffered from deficiencies in experimental design, which was difficult to overcome when analysing the data. It will be important, in designing future integrated monitoring studies, to draw on the experience of programs such as this to avoid some of the pitfalls which appear to be inherent in these types of large programs.     

Seed supply for coastal brackishwater shrimp farming: environmental impacts and sustainability

Globally, shrimp farming has been a significant agro-based economic activity since the early 1970s. Because it offered a huge immediate economic return, shrimp farming showed a booming expansion and soon became a multimillion dollar industry. However, it has been under extreme criticism because of its devastating ecological and socio-economic impacts. Because seed is the primary input, the impact from farming has started from the source of seed supply, so that not only are natural stocks of shrimp seeds now overexploited worldwide but seed collection activities also significantly reduce stocks of other living resources. Although hatcheries were developed as potential alternative and have replaced the natural seed source to a great extent, large-scale hatchery productions provide a potential source of coastal pollution. However, this area is still poorly studied. The present paper provides a review of the environmental impacts of the wild shrimp seed fishery as well as the possibility of environmental degradation from artificial shrimp seed production in hatcheries.     

The changing role of ecohydrological science in guiding environmental flows

Abstract

The term “environmental flows” is now widely used to reflect the hydrological regime required to sustain freshwater and estuarine ecosystems, and the human livelihoods and well-being that depend on them. The definition suggests a central role for ecohydrological science to help determine a required flow regime for a target ecosystem condition. Indeed, many countries have established laws and policies to implement environmental flows with the expectation that science can deliver the answers. This article provides an overview of recent developments and applications of environmental flows on six continents to explore the changing role of ecohydrological sciences, recognizing its limitations and the emerging needs of society, water resource managers and policy makers. Science has responded with new methods to link hydrology to ecosystem status, but these have also raised fundamental questions that go beyond ecohydrology, such as who decides on the target condition of the ecosystem? Some environmental flow methods are based on the natural flow paradigm, which assumes the desired regime is the natural “unmodified” condition. However, this may be unrealistic where flow regimes have been altered for many centuries and are likely to change with future climate change. Ecosystems are dynamic, so the adoption of environmental flows needs to have a similar dynamic basis. Furthermore, methodological developments have been made in two directions: first, broad-scale hydrological analysis of flow regimes (assuming ecological relevance of hydrograph components) and, second, analysis of ecological impacts of more than one stressor (e.g. flow, morphology, water quality). All methods retain a degree of uncertainty, which translates into risks, and raises questions regarding trust between scientists and the public. Communication between scientists, social scientists, practitioners, policy makers and the public is thus becoming as important as the quality of the science.

Editor Z.W. Kundzewicz

Citation Acreman, M.C., Overton, I.C., King, J., Wood, P., Cowx, I.G., Dunbar, M.J., Kendy, E., and Young, W., 2014. The changing role of ecohydrological science in guiding environmental flows. Hydrological Sciences Journal, 59 (3–4), 433–450     

The Gulf: A young sea in decline

This review examines the substantial changes that have taken place in marine habitats and resources of the Gulf over the past decade. The habitats are especially interesting because of the naturally high levels of temperature and salinity stress they experience, which is important in a changing world climate. However, the extent of all natural habitats is changing and their condition deteriorating because of the rapid development of the region and, in some cases from severe, episodic warming episodes.Major impacts come from numerous industrial, infrastructure-based, and residential and tourism development activities, which together combine, synergistically in some cases, to cause the observed deterioration in most benthic habitats. Substantial sea bottom dredging for material and its deposition in shallow water to extend land or to form a basis for huge developments, directly removes large areas of shallow, productive habitat, though in some cases the most important effect is the accompanying sedimentation or changes to water flows and conditions. The large scale of the activities compared to the relatively shallow and small size of the water body is a particularly important issue.Important from the perspective of controlling damaging effects is the limited cross-border collaboration and even intra-country collaboration among government agencies and large projects. Along with the accumulative nature of impacts that occur, even where each project receives environmental assessment or attention, each is treated more or less alone, rarely in combination. However, their combination in such a small, biologically interacting sea exacerbates the overall deterioration. Very few similar areas exist which face such a high concentration of disturbance, and the prognosis for the Gulf continuing to provide abundant natural resources is poor.     

Holistic environmental assessment and offshore oil field exploration and production

According to UK Government surveys, concern for the environment is growing. Environmental regulation of the industry is becoming wider in its scope and tougher in its implementation. Various techniques are available to assess how the industry can drive down its environmental impact and comply with environmental regulation. Environmental Assessments (EA) required by European law do not cover the whole life cycle of the project that they are analysing. Life Cycle Analysis (LCA) was developed to assess the environmental loadings of a product, process or activity over its entire life cycle. It was the first technique used in environmental analysis that adopted what was described as a holistic approach. It fails this approach by not assessing accidental emissions or environmental impacts other than those that are direct. Cost Benefit Analysis (CBA) offers the opportunity to value environmental effects and appraise a project on the basis of costs and benefits. Not all environmental effects can be valued and of those that can there is considerable uncertainty in their valuation and occurrence. CBA cannot satisfactorily measure the total environmental risk of a project. Consequently there is a need for a technique that overcomes the failures of project-level EA, LCA and CBA, and assesses total environmental risk. Many organizations such as, the British Medical Association, the European Oilfield Speciality Chemicals Association, the Royal Ministry of Petroleum and Energy (Norway) and Shell Expro now recognize that a holistic approach is an integral part of assessing total risk. The Brent SPAR case study highlights the interdisciplinary nature required of any environmental analysis. Holistic Environmental Assessment is recommended as such an environmental analysis.     

Assessment of Anthropogenic Impact on Marine Ecosystems and Biological Resources in the Process of Oil and Gas Field Development in the Shelf Area

Current methodology of environmental impact assessment in connection with the environmental consequences of hydrocarbons production in the shelf area is analyzed. Basing on the ecosystem approach, a scheme of environmental impact estimates is suggested, envisaging the use of a set of gradations (scales) to characterize spatial and temporal scope of impacts and their consequences, as well as criteria (thresholds) of impact permissibility, taking into account the natural variability in the population and ecosystem parameters. Estimates of the environmental and fishery-related consequences of hydrocarbon production in the sea shelf area at different stages of the process are compared to the available measured and calculated data. The suggested scheme of environmental impact assessment and criteria of permissible impacts are recommended for expert analysis, forecasting, and monitoring of the environmental situation in the sea shelf areas of Russia under the conditions of anthropogenic impact.     

Global climate change and its impacts on water resources planning and management: assessment and challenges

Population explosion and its many associated effects (e.g. urbanization, water pollution, deforestation) have already caused enormous stress on the world’s fresh water resources and, in turn, environment, health, and economy. According to latest World Health Organization estimates, about 900 million people still lack access to safe drinking water, about 2.5 billion people lack access to proper sanitation, millions of people die every year from water-related disasters and diseases, and economic losses in the order of billions of dollars occur due to water-related disasters. With the global climate change anticipated to have threatening consequences on our water resources and environment both at the global level and at local/regional levels (e.g. increases in the number and magnitude of floods and droughts, increases in sea levels), a general assessment is that the future state of our water resources will be a lot worse than it is now. The facts that over 300 rivers around the world are being shared by two or more nation states and that there are already numerous conflicts in the planning, development, and management of water resources in these basins further complicate matters for future water resources planning. In view of these, any sincere effort towards proper management of our future water resources and resolving potential future water-related conflicts will need to overcome many challenges. These challenges are both biophysical science-related and human science-related. The biophysical science challenges include: identification of the actual causes of climate change, development of global climate models (GCMs) that can adequately incorporate these causes to generate dependable future climate projections at larger scales, formulation of appropriate techniques to downscale the GCM outputs to local conditions for hydrologic predictions, and reliable estimation of the associated uncertainties in all these. The human science challenges have social, political, economic, and environmental facets that often act in an interconnected manner; proper ‘communication’ of (or lack thereof) our climate-water ‘scientific’ research activities to fellow scientists and engineers, policy makers, economists, industrialists, farmers, and the public at large crucially contributes to these challenges. The present study is intended to review the current state of our water resources and the climate change problem and to detail the challenges in dealing with the potential impacts of climate change on our water resources.     

Interactions between diatoms and fine sediment

Excessive mobilization and delivery of fine sediments to water bodies has detrimental impacts on those biotic elements used for waterbody status classification, including macroinvertebrates, fish and macrophytes. The relationship between fine sediment and diatoms is a reciprocal one, with diatoms influencing the production and retention of fine sediments, as well as being impacted by fine sediment derived from the catchment. Diatoms can increase the retention of fine sediments in benthic environments as a result of various mechanisms, including shear stress modification, surface adhesion and bed clogging. Enhanced retention of fines can have important implications for the transfer and fate of sediment‐associated nutrients and contaminants. Excessive fine sediment loadings impact diatom assemblages via shading, burial and scouring. Indirect impacts of increased fine sediment stress can result from changes in habitat availability, herbivory or predator changes, which cascade down the food chain. Indices based on the relative abundance of motile species have been proposed for using diatoms to assess waterbody status. However, disentangling the potential confounding impacts of alternative environmental stressors on these simplistic indices remains a significant challenge. Coupling sediment pressure models, capable of predicting the potential impact of mitigation, with meaningful diatom‐based indices, remains a challenge for catchment planning for sediment abatement and the attainment of improved, or protection of, ecological status. Existing targets for sediment management in river catchments are largely based on relationships between sediment stress and impacts on fish, but these thresholds have been widely criticized. There remains a need to develop generic modelling toolkits coupling sediment stress and impacts on a range of biological quality elements to support a weight‐of‐evidence approach. Copyright © 2012 John Wiley & Sons, Ltd.     

Environmental Impact Assessment of High Pressure Water Scrubbing Biogas Upgrading Technology

The aim of this work was to assess the burdens of a process in terms of environmental and health impacts, resource depletion issues, and energy demand based on the ability of the Life Cycle Assessment methodology to link the environmental impacts with the mass and energy flows. The analysis was done in terms of process and environmental performances of high pressure water scrubbing (HPWS) system applied for biogas upgrading. The application of process simulation based on the Aspen Plus® software has been considered as supportive for the calculation of mass and energy balances. Data processed using GaBi 4: Software showed that global warming, acidification, and human toxicity potentials were the main impact categories associated with the HPWS process. These indicators are largely related to the exhaust gas from the desorption column and the indirect emissions generated during energy consumption. The life cycle inventory study resulted in the development of a database with a vast inventory of data regarding HPWS technology. A basis for assessing potential improvements in the environmental performance of the system is provided. Future studies in this area will address the economical evaluation of the HPWS technology, so as to maximize economic efficiency and minimize environmental impacts.     

Integrated Catchment Modelling

The recent drought in the UK has focused attention on the requirement for more effective groundwater management practices in order to reduce the interference of groundwater abstraction on river flows to acceptable levels. Quantification of the impacts and the assessment of alternative management strategies requires the use of mathematical models. An Integrated Catchment Management Model is described which permits the direct assessment of alternative groundwater management practices on river flows. The model utilises a modified version of the Stanford Watershed Model for groundwater recharge estimation and for the computation of the surface and interflow components of runoff. The river system is incorporated implicitly in an integrated finite difference groundwater model. Groundwater flow to or from the river system is computed as a function of river level, which in turn is related to stage discharge characteristics of discrete reaches of the river system. The model has now been applied to a number of important groundwater systems in southern and eastern England. The calibration and verification results achieved in application to the River Allen catchment are presented. The approach maximises the use of readily available hydrological and hydrogeological information, and gives the water resources planner a sound framework and support for decision making.     

Use of point scale models to improve conceptual understanding in complex aquifers: An example from a sandstone aquifer in the Eden valley,Cumbria, UK

Understanding catchment functioning is increasingly important to enable water resources to be quantified and used sustainably, flood risk to be minimized, as well as to protect the system from degradation by pollution. Developing conceptual understanding of groundwater systems and their encapsulation in models is an important part of this understanding, but they are resource intensive to create and calibrate. The relative lack of data or the particular complexity of a groundwater system can prevent the development of a satisfactory conceptual understanding of the hydrological behaviour, which can be used to construct an adequate distributed model. A time series of daily groundwater levels from the Permo-Triassic sandstones situated in the River Eden Valley, Cumbria, UK have been analysed. These hydrographs show a range of behaviours and therefore have previously been studied using statistical and time series analysis techniques. This paper describes the application of AquiMOD, impulse response function (IRF) and combined AquiMOD-IRF methods to characterize the daily groundwater hydrographs. The best approach for each characteristic type of response has been determined and related to the geological and hydrogeological framework found at each borehole location. It is clear that AquiMOD, IRF and a combination of AquiMOD with IRF can be deployed to reproduce hydrograph responses in a range of hydrogeological settings. Importantly the choice of different techniques demonstrates the influence of differing processes and hydrogeological settings. Further they can distinguish the influences of differing hydrogeological environments and the impacts these have on the groundwater flow processes. They can be used, as shown in this paper, in a staged approach to help develop reliable and comprehensive conceptual models of groundwater flow. This can then be used as a solid basis for the development of distributed models, particularly as the latter are resource expensive to build and to calibrate effectively. This approach of using simple models and techniques first identifies specific aspects of catchment functioning, for example influence of the river, that can be later tested in a distributed model.     

Impacts of urbanisation on hydrological and water quality dynamics,and urban water management: a review

ABSTRACT

As urban space continues to expand to accommodate a growing global population, there remains a real need to quantify and qualify the impacts of urban space on natural processes. The expansion of global urban areas has resulted in marked alterations to natural processes, environmental quality and natural resource consumption. The urban landscape influences infiltration and evapotranspiration, complicating our capacity to quantify their dynamics across a heterogeneous landscape at contrasting scales. Impervious surfaces exacerbate runoff processes, whereas runoff from pervious areas remains uncertain owing to variable infiltration dynamics. Increasingly, the link between the natural hydrological cycle and engineered water cycle has been made, realising the contributions from leaky infrastructure to recharge and runoff rates. Urban landscapes are host to a suite of contaminants that impact on water quality, where novel contaminants continue to pose new challenges to monitoring and treatment regimes. This review seeks to assess the major advances and remaining challenges that remain within the growing field of urban hydrology.

Editor M.C. Acreman; Associate editor E. Rozos     

Restoration of wadi aquifers by artificial recharge with treated waste water

Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the country's treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands.     

Conventional Oil—The Forgotten Part of the Water-Energy Nexus

The impacts of unconventional oil and gas production via high-volume hydraulic fracturing (HVHF) on water resources, such as water use, groundwater and surface water contamination, and disposal of produced waters, have received a great deal of attention over the past decade. Conventional oil and gas production (e.g., enhanced oil recovery [EOR]), which has been occurring for more than a century in some areas of North America, shares the same environmental concerns, but has received comparatively little attention. Here, we compare the amount of produced water versus saltwater disposal (SWD) and injection for EOR in several prolific hydrocarbon producing regions in the United States and Canada. The total volume of saline and fresh to brackish water injected into depleted oil fields and nonproductive formations is greater than the total volume of produced waters in most regions. The addition of fresh to brackish “makeup” water for EOR may account for the net gain of subsurface water. The total amount of water injected and produced for conventional oil and gas production is greater than that associated with HVHF and unconventional oil and gas production by well over a factor of 10. Reservoir pressure increases from EOR and SWD wells are low compared to injection of fluids for HVHF, however, the longer duration of injections could allow for greater solute transport distances and potential for contamination. Attention should be refocused from the subsurface environmental impacts of HVHF to the oil and gas industry as a whole.     

New estimates of future changes in extreme rainfall across the UK using regional climate model integrations. 1. Assessment of control climate

Widespread major flood events in both the UK and Europe over the last decade have focussed attention on perceived increases in rainfall intensities. The changing magnitude of such events may have significant impacts upon many sectors, particularly those associated with flooding, water resources and the insurance industry. Here, two methods are used to assess the performance of the HadRM3H model in the simulation of UK extreme rainfall: regional frequency analysis and individual grid box analysis. Both methods use L-moments to derive extreme value distributions of rainfall for 1-, 2-, 5- and 10-day events for both observed data from 204 sites across the UK (1961–1990) and gridded 50 km by 50 km data from the control climate integration of HadRM3H. Despite differences in spatial resolution between the observed and modelled data, HadRM3H provides a good representation of extreme rainfall at return periods of up to 50 years in most parts of the UK. Although the east–west rainfall gradient tends to be exaggerated, leading to some overestimation of extremes in high elevation western areas and an underestimation in eastern ‘rain shadowed’ regions, this suggests that the regional climate model will also have skill in predicting how rainfall extremes might change under enhanced greenhouse conditions.     

Groundwater Availability as Constrained by Hydrogeology and Environmental Flows

Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes‐St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications.