case studies - orange fish sundays
Orange-Fish Sundays: Meeting Irrigation Needs in the Eastern Cape
Modelling & Decision Support System for Complex Inter-basin Water Transfer

The Orange-Fish-Sundays River System is an inter-basin water transfer scheme – one of the most prominent ones in South Africa. The water that it provides, meets the hefty irrigation demands in the Eastern Cape region. However, declining downstream water quality in the Fish and Sundays Rivers and water losses from excessive spills and leakages, required an efficient water management system to be put into place. We provided state-of-the-art hydrodynamic modelling services and a customised Decision Support System (DSS) to enable more informed management of the river waters. The outcome: substantial water and financial savings and efficient management of a much-needed water resource.

Orange, Fish and Sundays – rivers in the spotlight of ‘demand’

The Orange-Fish-Sundays River System in the Eastern Cape region of South Africa consists of an extensive system of canals, tunnels, rivers, dams and diversion weirs. The inter-basin water transfer scheme between them is one of the primary bulk water transfer schemes in South Africa. The water from these rivers is crucial for meeting the hefty irrigation demands of the region. For this purpose, water is transferred from the Gariep Dam on the Orange River to the Great Fish and Sundays Rivers, via the 82km long Orange Fish Tunnel. The total water demand on the system is close to 700 million m3 per annum – a significant amount that requires proper management

The Great Fish River and Little Fish Canal diversion at Elandsdrift Barrage

Water wastage – impact on quality and quantity

The system is highly dependent on the demands of the water users and their orders. However, users were often ordering more water than required. As a result, more wa-ter was being released to them than they actually needed. Excessive water used for irrigation progressively in-creased the groundwater salinity in the region. Conse-quently, the quality of the Fish-Sundays River System de-teriorated downstream, due to increasing salinity. Addi-tionally, large amounts of water were being lost due to leakage and excessive spills – effectively wasting the greatly needed resource.

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Due to a lack of information, it was getting difficult to sup-port and defend decisions for a better control of water releases. It became necessary to obtain better information about critical indicators that would help manage the sys-tem more effectively.

The solution – a real-time DSS

Our solution – a customised DSS – mainly involved three components:

  • Monitoring: Our solution integrates real-time water level and water quality data from 32 monitoring stations in the field. It also includes water requirement data from more than 150 downstream water users.

  • Modelling: The DSS uses MIKE 11 hydrodynamic model simulations to assist water resource operators and managers with seven operational release hydrographs. The hydraulic model network includes four dam struc-tures and over 1,000 km of rivers, canals and tunnels.

  • Forecasts: The system is used to provide short-term (seven-day forecast lead time) early warning decision support in an operational context to ensure that water of acceptable quality is supplied to users. Furthermore, the solution uses web-based information ‘dashboards’ to disseminate information to all relevant stakeholders.

The DSS Dashboard site for the solution

SUMMARY

Client

Department of Water Affairs (DWA), South Africa

Challenge

  • High water demand for irrigation – up to 700 million m3 per annum

  • Overall shortage of water required for irrigation

  • Water and associated financial losses during inter-basin water transfer

  • More water used for irrigation than required, increasing groundwater salinity.

  • Degraded quality of downstream river water due to high salinity.

Solution

  • Rehabilitation of monitoring stations to collect accurate real-time operational data State-of-the-art hydrodynamic modelling based on this data

  • Decision Support System for operational management of the customised water transfer

  • Involvement of stakeholders for better information provision to the system

  • Capacity building to make operators independent and

Value

  • Substantial savings on water losses

  • Significant financial savings due to efficient water management

  • Reduced salinity and improved water quality via control of water

Location/Country

Orange-Fish-Sundays River System, Eastern Cape Region, South Africa.

Overcoming obstacles and making the DSS a success

  • The skills required to run the system were not available locally. We engaged extensively with the client and stakeholders to develop those skills.

  • Obtaining accurate data was a major problem. We, along with the stakeholders, identified and rehabilitated structures to provide better information to the system

  • Accurate water orders influence the model perfor-mance and impact releases. Users were initially not complying with the water orders and actually over-ordering and under-using water in many circumstanc-es. To address this issue, we carried out an innovative implementation of a water audit. We provided the in-formation to DWA and Water User Associations to help them address problem areas in terms of water use.

Visible benefits

Initial investigations show that the DSS has helped to visi-bly reduce the amount of water transferred through the Orange Fish Tunnel, while effectively meeting irrigation needs.

An example of the hardware at one of the DWA real-time river monitoring points

It rained heavily in the catchment in the 2011-2012 peri-od. During this time, our model helped to manage the available water more optimally by utilising rain fall in the catchment better – thereby saving water releases from Gariep. Additionally, with the real-time information and summary indicators, it is now possible to determine whether irrigators are using the water efficiently based on their demands.

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