Using WEAP to create integrated water resource management tools
This case study is part of the SEI Urban Toolbox for Liveable Cities which has been developed by the SEI Initiative on City Health and Wellbeing. The Urban Toolbox is a collection of tools, developed within SEI or in coordination with SEI, aimed at supporting planning and decision-making for improving the health, well-being and resilience of city residents and urban systems more broadly.
This case study demonstrates how the Water Evaluation and Planning (WEAP) Tool can be used to support water resource planning.
The Lake Victoria (LV) region, comprising parts of Uganda, Kenya and Tanzania, is experiencing some of the highest urban growth rates in Africa. With the livelihood of close to 30 million people directly and indirectly dependent on the Lake Victoria ecosystem, effective resource management is necessary for ensuring the economic welfare of the regional population, as rapid changes in population size and composition, industrialization and consumption patterns create new pressures.
The Millenium Development Goals (MDGs) guide development investment toward expanding water and sanitation to all citizens, driven by the MDG of reducing by half the proportion of people without sustainable access to safe drinking water and basic sanitation by 2015. Governments support these endeavors with subsidized urban water production, and in some cases, sanitation services. However, subsidized piped water tariffs are too low to support long-term water infrastructure investments beyond daily operation and maintenance. As a result, governments continue to rely on donor support for major infrastructure investments in the water and sanitation sector.
Towards meeting the MDG goals, utilities in the LV region are working closely with UN-Habitat, the lead facilitator between development agencies and the water utility sector. As part of capacity building efforts, integrated water resource management (IWRM) platforms are being investigated as tools for utilities to build comprehensive water management plans, especially in response to dual pressures of demand growth and climate change.
This paper presents IWRM models built using the Water Evaluation And Planning (WEAP) decision support system, for three pilot towns in the LV region – Bukoba (Tanzania), Masaka (Uganda), and Kisii (Kenya). The objectives of this paper were (1) to examine how climate, demography and infrastructure impacts water utility performance in three east African towns; and (2) to develop IWRM models that integrate above aspects in a single platform.
*Thiscase study is an abridged version of the original text, which can be downloaded from ScienceDirect here. Please access the original text for more detail, research purposes, full references, or to quote text. A summary of the report is outlined below.
Methods and Tools
Located in equatorial East Africa, Lake Victoria is the largest lake in Africa, filling a shallow depression between the eastern and western arms of the East African Rift Valley 1100 m above sea level. The basin, 251,000 km2 in area, straddles six countries – Uganda, Tanzania, Kenya, Rwanda, Burundi and the Democratic Republic of Congo.
The three selected towns to study were Bukoba (Tanzania), Masaka (Uganda), and Kisii (Kenya). These towns derive their water supply from local streams, wetlands and Lake Victoria. Out of the three towns, Kisii currently has the most challenges both financially and in terms of demand coverage. In Kisii and Bukoba, electricity costs and losses (categorized as ‘‘unaccounted water (UAW)’’ represent dominant challenges
IWRM models were built for each utility at a monthly time step using WEAP. WEAP is a comprehensive water resources software that fully integrates physical hydrology with priority-driven water resources allocation, and is specifically built to support policy and planning by investigating alternative management responses to multiple drivers – climate, landuse and demographic change – with the help of an intuitive GIS-based GUI.
The approach comprised of (i) building water supply and demand network schematics, and populating the model objects with data gathered from questionnaires, key informant interviews, field visits and utility reporting, (ii) calibrating the models against existing system performance (the calibrated models are referred to as ‘reference models’ henceforth) and (iii) developing and running projections for 2010–2050 that were of key interest to each utility
Outcomes and Impacts
The IWRM models that were built highlight key findings for each town. Most notably, these models provide useful indications of the timing of major investment in infrastructure improvements and expansion, and the size of the expansion required.
In Masaka, water supply to meet current demand is more capacity limited than water availability (hydrology) limited. In the short term, just delivering water at design capacity could meet 100% of current demand, suggesting that this be the first priority for the utility. Under the wetter expected climate scenario, water availability continues to be sufficient until 2020 as long as water could be produced at current design capacity. Capacity expansion to double current design capacity would be sufficient to meet expected demand until 2050 under wetter climate conditions.
In Bukoba, reducing losses gives only marginal benefits in the first decade. Expansion to double current capacity would meet all projected demand until 2050. Kisii represents the most challenging of all the towns studied. Like in Bukoba, reduction of losses is not sufficient to improve demand coverage substantively. The need for major infrastructure expansion is most urgent in Kisii. Another contrast with Masaka and Bukoba, is that the minimum goals of meeting operating costs with revenues is not likely to be met in Kisii even if expansion is in place. Recognizing this situation, utility managers are actively considering several options including building mini hydropower to reduce the high electricity costs of their operations.
The unavailability of hydro-climatic data highlights one of the key limitations of the current models for Kisii and Bukoba, because water availability from surface water sources could not be identified. In Bukoba, with Lake Victoria as one of its sources, this currently poses a relatively lesser challenge than in Kisii. However, a true integration of climate and hydrology with infrastructure and demand, as demonstrated in Masaka, should be the goal for utilities in the LV region. Even in Masaka, the short time series precluded the traditional split-sample calibration and validation exercise, potentially reducing the robustness of the hydrologic simulation.
Urban water planning must happen in the context of regional, multi-sectoral planning and biophysical feedbacks (e.g. water quality impacts of increased development in Masaka). In this context, comprehensive IWRM platforms such as WEAP offer additional analytical abilities that should be noted. For example, imposing an in-stream flow requirement, and water quality constraints downstream of the intake and wastewater treatment plans, would be an effective way of ensuring that urban water supply into the future does not compromise ecosystem integrity and equity for downstream users. Implementing these rules into IWRM models is not difficult – rather, strong policy and regulatory frameworks are needed at institutional and governance levels such that it becomes a normal practice of urban planners and utility managers.
Although variable costs and revenues were included in the models, they did not include the investment costs corresponding to the infrastructure expansion scenarios. This would require a specific cost-benefit analysis of proposed sites.