Objectives

• to produce updated and extended hydrological sequences for the basin as a whole.
• to ensure that the hydrological data sets are easily accessible for any future work

Main Activities

• Provision of appropriate Capacity Building in a number of key areas agreed with each basin state
• Recommendations on appropriate protocols and procedures for data collection and data sharing throughout the basin
• Proposals on a data acquisition and display system to be adopted by all four basin states
• Assessment of Required Improvements to the Existing Gauging Networks
• Extension of Naturalized Flow Data

Conclusions

Capacity Building

Capacity in basic hydrometry is lacking, particularly in Lesotho and Botswana, both in terms of existing personnel being sufficiently capacitated and shortage of staff. In Botswana there is a serious need to develop capacity within the Hydrology Division. In Namibia and South Africa there is a shortage of staff, although essential systems appear to be operating in each country. There is a need to improve the quality of hydrological data throughout the basin. This could be achieved through a combination of infrastructure/equipment related measures and improved capacity and personnel levels.

Rainfall Measurement

Although certain areas of the Orange/Senqu basin still have adequate coverage of rainfall
gauges, there has been a significant reduction in operating rainfall stations in most of the sub-catchments of the basin. The current density of rainfall stations that are still open and used in the analysis ranges from between 0.3 and 3.2 gauges per 2500 km2.

Streamflow gauges

Although there appears to be an adequate coverage of the flow gauging stations within the
Orange/Senqu basin, it is of utmost importance that at least the stations used for the
hydrological extension work be maintained to ensure ongoing monitoring. This will ensure that the effects of the ever-increasing water and land-use impacts can be assessed and that the impact of projected trends in the climate can be monitored. Once again the high runoff areas, such as the Senqu (SE), Caledon (CA), Upper Vaal (VU) and the Upper orange (OU), should receive adequate attention when it comes to monitoring.

Modelling

A relatively fine spatial resolution hydrological model has been developed and it is essential to update the model at regular intervals with land-use changes as they occur to ensure that the hydrological database remains representative. In the Senqu River basin, it may be necessary to revisit the original “agreed hydrology” since it is now possible to create a better rainfall/runoff calibration due to the additional 15 or 20 years of recorded streamflow data now available in Lesotho.

Recommendations

• Provision of technical support to both Botswana and Lesotho, perhaps through a technical assistant to assist in upgrading their hydrological monitoring operations so that the network is managed more effectively.
• Expansion of the DWA South African data acquisition and display system (which already includes selected Lesotho stations) to incorporate key Namibian stations, and the addition of a link to the Orange-Senqu gauging network via the ORASECOM portal.
• The rainfall data (historic and present day) for the higher runoff yielding catchments, Senqu (SE), Caledon (CA), Upper Vaal (VU) and the Upper orange (OU), should be reevaluated to ensure that the best available point sources are identified. These stations should remain operational to ensure that future analyses can be undertaken.
• With the projected effects of climate change it is very important to safeguard and even expand the basin’s rainfall monitoring network. This will help to establish if the projected effects are actually occurring and , if so, what impact they will have on the meteorological conditions and water resource capabilities.
• The original Senqu Basin Hydrology needs to be revisited. In the recalibration process undertaken during this study it was identified that the initial part of the natural record was simulated with a lesser standard deviation and with a slightly lower MAR than the observed portion of the record. An investigation is required to assess the possible impact on the yield if a more representative natural record is simulated based on a new calibration against the longer observed record

Source:

Support to Phase 2 of the ORASECOM Basin-wide Integrated Water Resources Management Plan

Funding Organisation(s):

GIZ

Date:

2011

Documents

Cerrar, S. 2011. Improvements to Gauging Network and Review of Existing Data Acquisition Systems Support to Phase 2 of the ORASECOM Basin-wide Integrated Water Resources Management Plan

Haasbroek, B. et al. 2011. Extension of Hydrological Records: Support to Phase 2 of the ORASECOM Basin-wide Integrated Water Resources Management Plan

Data

Data generated during this Work Package includes rainfall and streamflow timeseries, old study reports and WRSM2000 model configurations. 

Map and Diagrams

Orange-Senqu Catchment Delineations

Point Rainfall Gauges in the Orange-Senqu Basin

Catchment Rainfall Boundaries

Stream flow gauging stations and their catchment boundaries

Natural Incremental Runoff (mm/a) in the Orange-Senqu Basin

Natural Incremental Runoff (%MAP) in the Orange-Senqu Basin

WRSM200 Network of the Senqu River up to Oranjedraai

WRSM200 Network of the Caledon River up to Welbedacht Dam

WRSM200 Network of the Caledon River downstream from Welbedacht Dam

WRSM200 Network of the Upper Orange – Kraai and Aliwal

WRSM200 Network of the Upper Orange – D14 and D35

WRSM200 Network of the Upper Orange – Van der Kloof Incremental