One of the approaches that show promise regarding new directions in dealing with contemporary water issues is integrated water management (IWRM). The work leading to this thesis was financially supported by the University of Swaziland through a European Union funded project with the short title “Integrated Water Resources Management Systems”. DISCUSSION AND CONCLUSIONS IN LIGHT OF RECOMMENDATIONS FOR THE MANAGEMENT OF INTEGRATED WATER RESOURCES FOR FUTURE CONSIDERATION AND RESEARCH.
Current and projected future impacts of water withdrawals, in both absolute and relative terms, for domestic uses in rural areas on accumulated stream flows. Time series of annual sediment yield and rainfall in Subcatchment 6 Plot of annual sediment yield vs annual rainfall of Subcatchment 6 Comparison of sediment yield generating events in Subcatchment 6 for the hydrological years 1983/4 and 1990/1. Sediment yield produced per unit (mm) of rainfall from different land uses in Subcatchment 6. Grass_R - grassland in good conditions; Grass_C - current grass field conditions; Grass_D - grassland in poor conditions).
LIST OF TABLES
INTRODUCTION
Therefore, sound management of water resources is necessary to ensure equitable sharing of resources by users. This catchment is considered to be a microcosm of the hydrological problems of a large part of the country. The chapter concludes with a section on results and comments on model output verification.
ASPECTS OF INTEGRATED CATCHMENT MANAGEMENT (ICM) AND INTEGRATED WATER RESOURCES MANAGEMENT
- Definitions
- Integrating catchment information management
- Sustainability of Water Resources Development and Management
- Downstream international obligations
- Hydrological Modelling for Integrated Water Resources Management
It is also the responsibility of the government to provide leadership, technical and financial support for the development and management of water resources. The existing institutional arrangement for water resources development and management is based on the Water Act of 1968. The next section therefore discusses the barriers to modeling for integrated water resources management in developing countries.
DESCRIPTION OF THE STUDY AREA
A visual assessment of the soil map (Figure 3.5) suggests a relationship between physiology and the distribution of some of the soil sets in the Mbuluzi catchment. Most of the irrigation takes place in the eastern part of the catchment around Simunye and Mhlume (Figure 3.1), a region aptly called the "Sugar Belt". Dry farming is widespread in the middle and some areas in the upper parts of the catchment.
METHODOLOGY
- Applications of the ACRU Model
The model then produces outputs of the unmeasured or simulated variables that can be analyzed within the modeling system or by using other post-processing software such as spreadsheets and statistical packages. The output of the AeRUmodel has been successfully verified and the model has been widely used to provide solutions to a wide range of water resources-related problems in different climatic and physiographic conditions. It is against this background that the ACRU model was chosen for modeling the hydrological responses of the Mbuluzi catchment.
The ACRU hydrological modeling system was configured for the Mbuluzi catchment upstream of the Mozambique border to simulate flows for 40 sub-catchments over the 46-year period from 1 January 1950 to 31 December 1995. Maps, tables and graphs were produced to quantify the following hydrological components, on a sub-catchment (i.e. sub-Quaternary catchment): .. a) streams under base land cover condition, .. b) stream production under current land use conditions, .. c) the impact of current land use and water demand on stream production, and d) the impact of possible future land uses and water demands on stream production, e) sediment yields under current land use conditions, and . f) the potential effects of changes in land use and management. Knowing the apparent limitations of the modeling system, such as the inability to simulate water quality, river channel geomorphological dynamics and ecological regimes, the research was not designed to be a mega-exercise to model all aspects of IWRM.
The first step in setting up the ACRU model for distributed modeling was the delineation of the entire catchment within the boundaries of Swaziland into sub-catchments... to be relatively homogeneous, in a hydrological sense. The following list of requirements formed criteria for delineating the Mbuluzi catchment into sub-catchments: .. a) ideally for the representation of the runoff-generating process in ACRU, the sub-catchments should not be larger than 50 km2, except where a high level of homogeneity existed or where the rainfall station network was sparse, .. b) each sub-catchment had to be relatively homogeneous in terms of climate, soils and land cover, .. c) currently operational gauges with sufficiently long records, operating by the Water Resources Branch (WRB) in the Ministry of Natural Resources and Energy (MNRE) were designated as outlets of sub-catchments, .. d) confluences of major tributaries of the Mbuluzi River were located at the outlet of a particular sub- catchment, .. e) individual sub-catchments were demarcated at outflows of large dams, and f) each sub-catchment had to be a subset of a Quaternary Sub-catchment. This approach allows hydrological responses of different land uses to be explicitly modeled as separate units and land use impact scenarios that can be undertaken with ease.
The order in which the simulated runoff generated in one cell was to be directed to another cell and then from the upstream watershed to the downstream watershed was determined by the procedures described in Schulzeet at.
I LEGEND I
Verification of modelled streamflows at GS32
The difference between the sums of the monthly totals of streamflow is 25%, while the standard deviations of the simulated streamflow are approximately twice those of observed streamflow.
Comments on the verification studies
The GS32 station is strategically located as the last gauge dam before the Mbuluzi River crosses the international border with Mozambique (Figure 4.6). Standard deviation of observed values (mm) Standard deviation of simulated values (mm).. difference between standard deviations Kurtosis of observed values. At all sites the verification studies were carried out for periods ending no later than 1984, before the weirs were either washed away by floods (GS4 and GS32) or buried under deposited debris and sediment (GS3) following Cyclone Domonia, while the model input was the land cover from 1996 used.
Besides the situation being difficult to model, critical input information such as return flow from irrigated lands was not available. In light of these problems, the results of the verification studies were considered relatively good and acceptable.
Conclusions
It was therefore concluded that the AeRU model can be used to reliably simulate the hydrological dynamics and expected hydrological responses of possible land use changes in the Mbuluzi catchment, especially in relative terms. In the following chapters, the model is used to carry out impact studies in the catchment area.
MODELLING IMPACTS OF DIFFERENT LAND AND WATER USE SECTORS ON STREAMFLOWS
400- 500 -N Major rivers>500
MODELLING SEDIMENT YIELD IN THE MBULUZI CATCHMENT
- Introduction
- Using ACRU to Model Sediment Yield
- Soil erodibility factor, K
- Slope length and gradient factor, LS
- Land cover and management factor, C
- Conservation practices, P
Based on the 18 land cover classes identified in the Mbuluzi catchment (c£ Table 4.1), decision support systems, figures and. Factors representing the effects of support practices were estimated from Table 6.3 in conjunction with slope and farming practices found in the Mbuluzi catchment. Lack of measured sediment yield data in the Mbuluzi catchment made it impossible to conduct conventional verification studies.
The highest (more than 50 t.ha-I) values of sediment yield were simulated in SC32 in the north-eastern part of the catchment area (cf. Figure 6.2). Other high sediment yields were simulated in the upper-middle parts of the catchment (eg SC7). Moderate to high sediment yields were generated in the sub-catchments with MAP greater than 1000mm in the higher elevation areas (eg SC1).
Moderately low average annual sediment yields between 2.5 and 5 t.ha-l were simulated in the sub-catchments with large-scale irrigated sugarcane estates (eg SC29). It is noteworthy that sediment yields simulated in the grassland in poor hydrological condition are higher than those of subsistence agriculture between February and March. Replacing those areas of the current land cover that can be grazed and used with grass cover in poor hydrological conditions led to increases in simulated sediment yields in all the sub-catchments.
Soil erosion and heavy sediment loads in the Mbuluz catchment is a serious concern for some of the stakeholders, especially the large-scale irrigators who draw water from the Mnjoli dam.
DISCUSSION AND CONCLUSIONS IN THE LIGHT OF INTEGRATED WATER RESOURCES MANAGEMENT
Mushala (2000) recommends that catchment management should be based on an integrated approach. The IWRM approach recommends that the management of water resources is supported by an understanding of the nature and behavior of the environment and its subsystems, forms and extents of the system. Of equal importance to the technical or physical aspect of water resources is the understanding of human systems in water management.
The passage of the new water bill in Swaziland into a law has suffered some delays. This is crucial given that the Bill contains some of the somewhat controversial issues associated with modern water management, such as demand management, water pricing and the abolition of water ownership on land. The level of integration of the model at this stage is only between components of the physical system, ie.
Ahead of the promulgation of the new water law that will promote IWRM, the Water Resources Branch of Swaziland is upgrading its data capture, manipulation and storage systems to meet the information demands of IWRM. There is a general feeling that the water resources of the Mbuluzi River have been over-allocated in Swaziland, a sentiment also expressed by Matola (1999). The aid should be aimed at capacity building and training of local expertise in water resource management.
Regardless of the problems, IWRM nevertheless remains the best approach to sound and effective management of water resources.
RECOMMENDATIONS FOR FUTURE CONSIDERATION AND RESEARCH
Individual and organizational behavioral issues related to water resource simulation modeling and its role in integrated watershed management in southern Africa. Integrated catchment management philosophy and practice: Implications for water resources management in South Africa. An emerging form of public participation in natural resource management. Journal of the American Water Resources Association, 35.
Integrated water resource management: Who should lead, who should pay? Journal of the American Water Resources Association. World Water Resources Assessment - Phase 2: Estimates of current and future water availability for eastern and southern Africa. A survey of the spatial distribution of soil erosion in the Mbuluzi River Basin, Swaziland.
Linking the needs of economic and social development to water resources management through spatial planning (Midmar Integrated Planning Initiative). State of the Environmental Technical Paper Series (Inland Waters), Department of the Environment, Sport and Territories, Canberra. Assessment of the impacts of climate change on hydrology and water resources in South Africa.
School of Bioresources Engineering and Environmental Hydrology, University of Natal, Pietermaritzburg, RSA Report to South African Country Studies for Climate Change Programme.
