MODELLING AS A TOOL IN INTEGRATED WATER RESOURCES MANAGEMENT
Conceptual Issues and Case Study Applications
Report No 749/1/04

EXECUTIVE SUMMARY

1. BACKGROUND

This project, a component of the Hydrological Modelling Systems Programme funded by the WRC at the School of Bioresources Engineering and Environmental Hydrology (formerly the Department of Agricultural Engineering) at the University of Natal in Pietermaritzburg, commenced in 1996 and was completed in 2002.

a) Objectives

The project objectives were

• the development and applications of a linked agrohydrological modelling infrastructure (i.e. model plus databases and decision support systems)
• to assess benefits of integrated catchment management (ICM)
• in order to address and quantify real and contentious issues which characterise South African catchments, often under stress, and which make their management difficult with respect to, inter alia,
• the vagaries of climatic variability
• hydrological risk management
• multi-sectoral water demands
• land use intensification, e.g. by afforestation and sugarcane plantations
• land use extensification, e.g.by veld degradation
• best management practices in irrigation or
• future climates
• and where the benefits could imply, inter alia,
• taking cogniscance of the interactions of the natural with the social, political, legal and economic environments
• addressing impacts of land use and its change
• pro-actively planning catchment operations with respect to optimising land and water resources
• identifying environmentally sensitive areas within a catchment and
• identifying areas where conflict management could be undertaken with the aid of modelling.

b) Motivation and Method

The motivation for this project was that water related issues, which often result in conflicts over allocation and use, be managed holistically, through working partnerships between researchers and stakeholders. These stakeholders may be water users, land holders, environmental interest groups, communities and government agencies, as well as NGOs. Such holistic management would require, inter alia, versatile agrohydrological modelling tools with process representations and configurations appropriate for southern African conditions.

The ACRU modelling system was to be the 'carrier' for this project because it was deemed suitable to be applied simultaneously as a

• scenario planning model
• assessing alternative land and water uses and
• assessing impacts, sensitivities and thresholds on catchments
• a multi-specialist model
• providing a versatile modelling framework for further development and interlinkages to other models/modules and
• an operational model
• to be used in management decisions.

Apart from further model development, specialist fieldwork, decision support and database development, a major methodological focus of this project was to be the application of the model in appropriate case studies.

c) Directions given . . . directions taken

It was in the course of this project that major conceptual rethinking took place in regard to ICM, which is a very far-reaching overarching concept of water management and which, in hindsight, was found to be beyond the scope of a project such as this. The focus of this report is, therefore, rather on Integrated Water Resources Management, IWRM, which is a (still wide-ranging) subset of ICM (cf. Chapter 1). Simultaneously, the late 1990s saw major paradigm shifts in the management of water resources as well as, of course, the promulgation of the National Water Act of 1998. The ushering in of this Act had major repercussions on directions taken in, and research undertaken through, this project, and many of the chapters bear testimony to that.

In light of the project's objectives, motivations, methods and new directions which evolved during the project's duration, this report of 14 chapters is presented in three broad sections:

• Section A : Conceptual and Modelling Issues
  This consists of six chapters covering
• perspectives on integrated water resources management (IWRM)
• thoughts on, and concepts, basic premises and requirements of models for IWRM
• concepts, structure and typical applications of the ACRU agrohydrological modelling system
• background to impacts of land cover and land use on hydrological responses
• the use of detailed information in modelling and
• a framework for hydrological risk management, with examples from southern Africa.
• Section B : On Modelling Impacts of Land Use on Hydrological Responses
  This section contains a further six chapters which cover
• a forest hydrology decision support system
• a regional study on streamflow reduction activities by different land uses
• water use by, and water use efficiencies of, sugarcane
• a sensitivity study on competing land uses, viz. afforestation and irrigation
• compensatory forestry from riparian zone alien vegetation clearance and
• impacts of veld degradation and rehabilitation on catchment sediment yields.
• Section C : Looking Towards the Future
  This section has two chapters which address
• the application of seasonal rainfall forecasts to sugarcane yield forecasts and
• a threshold analysis on when, and where, climate change is likely to impact on water resources in South Africa.

A number of the chapters titles and most of the chapter subheadings have been posed as questions to which the respective contents provide some answers. Each chapter, while linked conceptually and contextually to the others, can in essence be read as an entity.