Developing new urban water supplies: investigating motivations and barriers to groundwater use in Cape Town

ABSTRACT

Many cities are experiencing increasing water resource stress. In Cape Town, South Africa, surface water supplies are at a record low due to a multi-year drought crisis which began in 2015. This paper analyzes the range of motivations, possibilities and obstacles related to diversifying Cape Town’s water supply system through the upscaling of groundwater resources. Drawing on insights from local experts, it is maintained that uncertainty surrounding groundwater and drought-management practices present significant barriers to Cape Town’s ongoing water diversification efforts. This paper provides further insight and discussion for future water planning in Cape Town, as well as for other urban, water-scarce, regions.     

Trends in instrumentation, control and automation and the consequences on urban water systems.

In recent years more and more on-line sensors have been used on different structures of urban water systems (UWS, i.e. wastewater treatment plants (WWTP), waterworks (WW), sewer systems). This development is influenced and driven by numerous trends, which will be discussed in this paper. For a better understanding, the discussion is illustrated with a factual example. The new possibilities of on-line measurement and automation technologies will also change the way as UWS will be planned, built and operated.     

Appraisal and optimization of agricultural water use in large irrigation schemes: I. Theory

A new approach on the functioning of an irrigation scheme has been presented. A mathematical representation of the irrigation system based on measured system properties, such as losses due to percolation and to poor management, in only a part of the system is used. This mathematical representation is termed an equivalent irrigation network. The merit of this approach is that it reduces the number of required streamflow measurements.When water amounts are measured for a number of paths in the irrigation network, so-called path efficiencies are obtained. The path efficiency is a measure of the amount of water lost along the way. The numerical model that simulates the operation of the irrigation system is based on the path efficiencies. This simulation model in turn is used to calculate different objective functions, corresponding with different optimization goals, like uniform water distribution, minimum groundwater extraction, minimum cost of water supply.This paper gives the theoretical background of the approach. The application to an actual irrigation scheme will be discussed in a second paper.     

Appraisal and optimization of agricultural water use in large irrigation schemes: II. Applications

In this paper, the theoretical approach presented in Part I is demonstrated by means of case studies on the irrigation schemes of Rio Mendoza and Rio Tunuyán in the Province of Mendoza, Argentina. The object of the case studies was the determination of optimal allocation of surface water to reduce the use of groundwater. Current and optimal conjunctive allocation of ground and surface water is studied by means of the developed simulation and optimization models.The second case study was designed on the basis of the experience gathered during the first one: each step of the case studies is compared. The comparison between the two case studies illustrates how to apply the proposed approach when the amount and quality of available data are different. For the more detailed Rio Tunuyán study, we determined the following physical characteristics of all terminal nodes: on-farm rotational intervals, mean water application depth, actual soil water storage capacity, crop water requirements, depth of groundwater table, aquifer transmissivity, and efficiency of groundwater use.The performance of the entire system is sensitive to changes in the water application depth, as it was shown by a simulation study.The application of our optimization approach to the conjunctive use of ground- and surface water showed that the total water requirements over a year can be met by a reassignment of water that reduces the total costs of a great amount.     

Macro,meso, and micro-efficiencies and terminologies in water resources management: a look at urban and agricultural differences

Efficiency of water resources is essential; just as important is the terminology that describes it. Paradoxes in terminologies used by various international institutions and professionals in the agricultural, urban and environmental domains are examined. Integrated terminologies are proposed, starting from flow-path types in water balance and expanded into the “macro, meso, and micro-efficiencies” (3ME) formulation. The 3ME is a systemic framework based on the principle of the conservation of mass, integrating water-flow paths of a water system, their beneficial and quality attributes (the usefulness criterion), climate, and two types of water totals. These terminologies, with nine examples for urban (three types) and agricultural areas (rainfed, surface, drip and sprinkler), are used to discuss the 3ME framework and possible flawed policy implications.     

Contribution of agricultural and non-agricultural use of pesticides to the environmental impact on aquatic life in regional surface water systems.

By means of a modelling tool an analysis was made of the local variation in the use of pesticides in the province of Utrecht in The Netherlands, and the potential environmental impact of pesticide emissions on the aquatic ecosystems. The aim of this study was to identify and quantify the major sources of pesticide use and environmental impact, taking the regional variation of pesticide use into account. The analysis was targeted at different levels: detailed (individual active substances, individual agricultural crops, civil land-use types, hydrological catchment basins) and globally covering agricultural use, non-agricultural use (some civil sectors) and recreational shipping. The results can be used for the (re)design of environmental monitoring programmes of pesticides in surface waters and for the development of region based policies towards sustainable pesticide use. The analysis tool that was developed is considered to be applicable for other regions as well.     

A decision support framework for sustainable urban water planning and management in new urban areas.

The paper discusses issues of decision support within the context of sustainable development and more specifically sustainable water cycle management to provide a context and a rationale for the decision support approach adopted within an on-going U.K. EPSRC-funded project, WaND. The paper proposes a set-up for a flexible, upgradeable, efficient and modular decision support framework and associated tools. Furthermore, the paper presents early prototypes of three decision support tools developed within the proposed framework including initial results for one of them.     

转变用水观念节约和保护水资源促进海河流域水资源的可持续利用

海河流域用水量急剧增加,废污水排放量大,导致水资源供需矛盾日益突出,水环境日益恶化.为促进水资源的可持续利用,必须转变观念,树立节水意识,完善水权和水市场制度,推进科技创新,有效防治污染,合理开发水资源.     

A new database on urban runoff pollution: comparison of separate and combined sewer systems.

For a long time people have questioned what the "best" sewer system is for limiting the pollution load released into the receiving waters. In this paper the traditional separate and combined sewer systems are compared using a pollution load balance. The investigation is based on measured concentration data for a range of pollutant parameters in the sewer from the new database "ATV-DVWK Datenpool 2001". The approach also accounted for the wastewater treatment plant outflow which contributes to the total pollutant load considerably. In spite of a number of neglected effects, the results show that the separate system is superior to the combined for some parameters only, such as nutrients, whereas for other parameters, e.g. heavy metals and COD, the combined system yields less total loads. Any uncritical preference of the separate system as a particularly advantageous solution is thus questionable. Individual investigations case by case are recommended.     

应用农业生产系统模型分析冬小麦-夏玉米轮作体系的农田水氮利用效率Ⅱ：模型的模拟验证与情景分析

应用经过参数灵敏度分析与标定后的农业生产系统模型（APSIM）,以北京市海淀区东北旺试验站为背景,探讨了不同灌溉、施肥、种植日期和种植密度等农艺措施下冬小麦和夏玉米的产量、水分利用效率及氮肥偏生产力的变化,以期探寻适合当地特定气候、土壤条件下的既能保证粮食稳产高产又能达到资源高效利用的田间管理措施。首先根据所搜集的1985-2005年统计年鉴中的产量数据对参数标定后的模型作了进一步的验证,结果表明：冬小麦和夏玉米产量的模拟值与年鉴统计值之间的平均相对误差分别是43％和21％。运用验证后的模型,基于所设计的9种不同的水氮管理情景进行了模拟分析,结果表明：冬小麦在播前、拔节期和开花期灌溉75ram;丰水年和平水年夏玉米在播前灌溉3lmm,枯水年夏玉米在播前和抽穗分别灌溉20mm,特枯水年夏玉米在播前和抽穗分别灌溉84mm;冬小麦在播前和拔节期分别施人氮肥43kg／hm^2和87kg／hm^2,夏玉米在苗期和大喇叭口期分别施人氮肥40kg／hm^2和80kg／hm^2.这样的节水省氮灌溉施氮方案不仅能够获得较高的粮食产量,还能获得较高的水分利用效率和氮肥偏生产力。     

应用农业生产系统模型分析冬小麦-夏玉米轮作体系的农田水氮利用效率I：模型参数的灵敏度分析与标定

以采集的北京市海淀区东北旺试验站大量的田间实测数据为基础,对农业生产系统模型（Agricultural Production Systems Simulator,APSIM）进行详细的参数灵敏度分析与标定,结果显示：标定模拟的土壤剖面体积含水量动态的精度较高,平均相对误差为13.41%;标定模拟的土壤剖面硝态氮浓度动态的精度较低,平均的相对误差为29.69%;标定模拟的冬小麦叶面积指数、生物量和产量的平均相对误差分别为36.49%、24.18%和32.31%;标定模拟的夏玉米叶面积指数、生物量和产量的平均相对误差分别为31.76%、35.84%和26.44%。以上标定模拟的精度就田间实际情况而言,总体是可以接受的。经过详细的参数标定后的APSIM模型将为深入探讨不同农田管理措施下水氮利用效率的长期变化提供可靠的定量分析手段。     

"城市双修"理念下城市水体修复策略探索 ——以武汉市北湖产业生态新城水系综合治理为例

为研究快速城镇化过程中城市水体面临的环境污染、生态破坏等问题,以武汉北湖产业生态新城水系综合治理为例,在水体现状分析评估基础上,结合"城市双修"工作的指导意见,注重水体与周边环境的良性互动,提出了改善水环境、强化水安全、提升水生态、塑造水活力的水体修复策略.研究成果可为其他地区水体修复提供参考.     

Instream restoration: its effects on lateral stream–subsurface water exchange in urban and agricultural streams in Southern Ontario

Instream restoration strategies do not generally consider the subsurface environment. The study of recently restored stream reaches can provide an opportunity to assess the impacts of restoration on surface–subsurface exchange. In this study, lateral hyporheic zones occurring in a constructed gravel bar and re‐meandered stream reach were examined, using hydrometric data in combination with differences in background conservative ion and tracer injection experiments. Both the constructed gravel bar and the meander bends induced lateral hyporheic exchange flow. In the gravel bar, lateral hyporheic exchange increased after a riffle‐pool sequence was constructed in the channel adjacent to the bar. The substrate in the meander bends had low saturated hydraulic conductivity, and the stream–subsurface exchange was limited despite the large change in channel configuration. These results suggest that to enhance and maintain stream–subsurface water exchanges, restoration projects that modify horizontal geometry should involve construction of vertical morphologic features, and where floodplain sediments are fine‐grained, the addition of coarse sediments should also be incorporated in the design. Copyright © 2007 John Wiley & Sons, Ltd.     

The use of modelling and reuse techniques in the development of water management systems in basins with limited water resources.

Drawing on experiences in New South Wales from 1950 to 1980 in modeling and re-use techniques in the development of desalination technology and its application in fresh water production for potable use, the paper describes how Australia realized its responsibilities in developing participative and sustainable approaches to land use and water resources management. An analysis of the lessons from the operation of the Bayswater zero-discharge power station significantly contributed to the debate on sustainable approaches, highlighting that no management policy of a water basin can be implemented without a model based on reliable data from all sectors (including the environment), and no management model can be implemented without the participation of all stakeholders. These ideals were reflected in the conception and establishment of the Murray-Darling Basin Commission. The Commission succeeded in bringing together all major stakeholders in this huge basin, though it took more than 15 years to do so. While widely recognized as one of the most advanced and successful experiences in integrated management of a drainage basin, it has still not achieved the reversal of many unsustainable agricultural practices, giving a clear indication of the difficulties and time required for producing sustainable solutions.     

Summary and conclusions from the SIWI Seminar for Young Water Professionals Drainage basin security--implications of virtual water trade and agricultural subsidies at regional, national and local levels.

This is a summary of the Young Water Professionals Seminar involving more than 50 young people from all over the world working with water. The presentations and following discussion were very lively and were about how subsidies and trade barriers imposed by the developed countries are influencing the income-generating capacity of millions of people in the developing world. Even though this is a very complex issue not easily resolved during the seminar it was also clear that there are some fundamental problems that need to be addressed. The importance of looking for solutions at different levels (i.e. local, regional, national) was highlighted as well as the policy of double standards, preaching free trade but only for the benefit of overdeveloped countries themselves. Further it was discussed how to achieve basin security through food security, and managing water for food security. The conclusion was that win-win solutions would be made if agricultural subsidies were to be completely removed.     

Workshop 3 (synthesis): climate variability, water systems and management options.

Addressing climate variability now will better prepare us for future impacts of climate change. Sustained, multi-stakeholder dialogue at local through national levels is an approach that will reach the widest audience, helped by tools that illustrate vulnerability such as the Climate Vulnerability Index. Integrated water resources management deals with managing for variability and change and is therefore highly appropriate for dealing with climate impacts.     

Applying sustainable water management concepts in rural and urban areas: some thoughts about reasons, means and needs.

Serving the world population with adequate drinking water and sanitation is an important prerequisite, not only to hygienic safety, but to prosperity and political stability as well, and will foster the adaptive capacity of the societies in the developing countries and beyond. To avoid hygienic and political disasters impacting the world economy, investment in water supply and sanitation must urgently be made. Whether the classical system of urban water supply and sanitation is appropriate to satisfy the needs of the developing world, however, and whether this system meets the general criteria of sustainability is questionable. The costs and the time needed for installation of sewers and wastewater treatment plants are tremendous. In water shortage areas, the amount of tap water required to transport pollutants to the treatment plant is hardly affordable. Recovery and re-introduction of valuable substances, including water, into the urban cycle of materials is impossible because of mixing and dilution effects inherent in the system. Decentralized water and wastewater management should be seriously taken into account as an alternative. Source separation of specific fractions of domestic and industrial wastewater, separate treatment of these fractions and recovery of water and raw materials including fertilizer and energy are the main characteristics of modern high-tech on-site treatment/reuse systems. Mass production of the key components of the system could reduce the costs of the treatment units to a reasonable level. On-site units could be installed independently of the development stage of the urban sewer system. In conjunction with building new housing complexes a stepwise improvement of the hygienic situation in urban and peri-urban areas could be achieved, therefore. Remote control of the satellite systems using modern telecommunication methods would allow reliable operation, and comfort for the users. Intensive research is required, however, to develop this system and bring it to a standard allowing efficient application worldwide.     

A new online monitoring and management system for accidental pollution events developed for the regional water basin in Ningbo, China

Due to urgency of the accidental pollution events (APE) on one side and the variability in water quality data on the other side, a new online monitoring and management system (OMMS) was developed for the purpose of sustainable water quality management and human health protection as well. The Biological Early Warning System (BEWS) based on the behavioral responses (behavior strength) of medaka (Oryzias latipes) were built in combination with the physico-chemical factor monitoring system (PFMS) in OMMS. OMMS included a monitoring center and six monitoring stations. Communication between the center and the peripheral stations was conducted by the General Packet Radio Service (GPRS) network transmission complemented by a dial-up connection for use when GPRS was unavailable. OMMS could monitor water quality continuously for at least 30 days. Once APEs occurred, OMMS would promptly notify the administrator to make some follow up decisions based on the Emergency Treatment of APE. Meanwhile, complex behavioral data were analyzed by Self-Organizing Map to properly classify behavior response data before and after contamination. By utilizing BEWS, PFMS and the modern data transmission in combination, OMMS was efficient in monitoring the water quality more realistically.     

Instrumentation, control and automation in the water industry--state-of-the-art and new challenges.

Instrumentation, control and automation (ICA) are key technologies in modern water and wastewater systems. Ever present disturbances make it necessary to automatically attenuate their consequences. A wastewater treatment system is load driven, while a water distribution system is demand driven. Despite the variability the system outputs have to be satisfactory. Economic realities encourages the application of ICA to make a maximum use of plant capacities. An increasing complexity of competing processes in a modern nutrient removal plant makes more elaborate control necessary. The final goal of protecting the environmental resources necessitates an integrated view of several interdependent systems, the collection, transport and treatment processes. In this integrating development ICA will be a decisive technology.     

Application of SEBAL approach and MODIS time-series to map vegetation water use patterns in the data scarce Krishna river basin of India.

Evapotranspiration (ET) from irrigated land is one of the most useful indicators to explain whether the water is used as "intended". In this study, the Surface Energy Balance Algorithm for Land (SEBAL) was used to compute actual ET from a Landsat7 image of December 29, 2000 for diverse land use in the Krishna Basin in India. SEBAL ETa varies between 0 to 4.7 mm per day over the image and was quantified for identified land use classes. Seasonal/annual comparison of ETa from different land uses requires time series images, processed by SEBAL. In this study, the Landsat-derived snapshot SEBAL ETa result was interpreted using the cropping calendar and time series analysis of MODIS imagery. The wastewater irrigated area in the basin has the highest ETa in the image, partly due to its advanced growth stage compared to groundwater-irrigated rice. Shrub and forests in the senescence phase have similar ETa to vegetable/cash crops, and ETa from grasslands is a low 0.8 mm per day after the end of the monsoon. The results indicate that wastewater irrigation of fodder and rice is sufficient to meet crop water demand but there appears to be deficit irrigation of rice using groundwater.