This part of the Institutes Web Page relates contributions, as far as hydrological analyses are concerned, that the IWR is making to the determination of Instream Flow Requirements (IFR) and the setting of the water quantity component of the Ecological Reserve for rivers. Prior to the 1998 changes to the South African Water Act, the IWR hydrology specialists were involved in several IFR Workshop studies which were carried out to determine the ecological flow requirements of some rivers prior to large scale water resource developments. Through this involvement certain hydrological analysis methods were developed to cater for the requirements of the other specialists involved in the studies. Since that time these methods and models have been further developed and incorporated into the SPATSIM software package.

The hydrological work that was required for an IFR, based on the Building Block Methodology (BBM) essentially involved three stages:

  • Preparation of representative time series of daily flow data for natural and (where possible) present day flow regimes. The IWR has frequently used its own daily rainfall-runoff model (the VTI model) for this purpose.
    Hughes, DA & Sami, K (1994) A semi-distributed, variable time interval model of catchment hydrology - structure and parameter estimation procedures. Journ. Hydrol., 155, 265-291.
    However, setting up such a model can be very resource intensive and a simpler approach that makes use of interpolation procedures from nearby gauged flow data has been found to be useful for IFR or Reserve workshop purposes.
    Hughes, DA and Smakhtin, V (1996) Daily flow time series patching or extension: a spatial interpolation approach based on flow duration curves. Hydrol. Sci. Journ., 41(6), 851-871).
    Where daily flow data are not available it is necessary to use monthly flow time series from the national database (WR90 or more recent updates) or using the Pitman monthly model.


  • Presentation of the hydrological data at the workshop. The other specialists rely on the hydrological specialist to be able to provide various statistics of flow (duration curve % points, for example), as well as graphical representations of various components of the daily time series. All of the IWRs modelling and time series analysis procedures used to be incorporated into a modelling and data analysis system called HYMAS, which was a DOS based suite of 'C' programs developed in the late 1980s and early 1990s.
    Hughes, DA, Murdoch, KA and Sami, K (1994) A hydrological model application system - a tool for integrated river basin development. In: C Kirby & WR White, Integrated River Basin Development, John Wiley & Sons
    HYMAS contained several low flow analysis procedures that are especially relevant to IFRs.
    Smakhtin, VY, Watkins, DA, Hughes, DA, Sami, K & Smakhtina, OY (1998) Methods of catchment-wide assessment of daily low-flow regimes in South Africa. Water SA, 24(3), 173-185.
    More recently some of the time series analysis and display procedures have been re-written for a Windows environment using DELPHI (TSOFT Utilities).
    Hughes, D A (1997) The cooperative development of a hydrological time series analysis and display software package. Proc. 8th South African National Hydrology Symposium, Pretoria, Nov. 1997.
    Since 2000 the SPATSIM software package (which incorporates TSOFT) has superceded all previous software developments in the Institute and is now available to any potential user.
    Hughes, DA (Editor) (2004) SPATSIM: An integrating framework for ecological Reserve determinations and implementation. Incorporating water quality and quantity components for rivers. Report to the Water Research Commission.


  • Establishment of 'rules' to determine when flows of different magnitudes (equivalent to so-called maintenance or drought requirements) should occur in the modified flow regime in response to the natural variations in flow that would be expected in the river. This is similar to the concept of determining the % assurance of different supply levels for abstractors. The IWR has developed a daily model (IFR model) to simulate likely flow scenarios to facilitate the setting of these rules by the workshop participants.
    Hughes, D A, O'Keeffe, J, Smakhtin, V and King, J (1997) Development of an operating rule model/ to simulate time series of reservoir releases for instream flow requirements. Water SA, 23(1), 21-30).
    A further model can be used to provide an approximate estimate of the impact on the yield of a reservoir of reserving water to satisfy the IFR.
    Hughes, D A and Ziervogel, G (1998) The inclusion of operating rules in a daily reservoir simulation model to determine ecological reserve releases for river maintenance. Water SA, 24(4), 293-302).

The changes to the Water Act and the need to begin implementing the concept of the Ecological Reserve has meant that estimates of the requirements of rivers will have to be made at many more sites than previously. The lengthy, and often expensive processes, involved in traditional IFR workshops are somewhat inappropriate to apply to a large number of sites and therefore the concepts of the Intermediate Determination of the Reserve and the Desktop Estimate were developed. The Intermediate Determination is seen as a somewhat more rapid version of the full IFR, inevitable resulting in an answer at a lower level of confidence. The Desktop Estimate is seen as a very low confidence but quick estimate that could, for example, be generated for the whole of the country as a 'first guess' prior to more detailed studies being undertaken. More detailed information on the development of ideas to support these two concepts can be found at the web site of the Institute for Water Quality Studies, a section of DWAF and the group who are coordinating the research and implementation.

There are five main areas where contributions are being made, or have been made, by some sections of the IWR:

Desktop Estimate Decision Support System

The development of techniques and software (DSS) to facilitate the estimation of a first guess (referred to here as the Desktop Estimate) of the quantity component of the Ecological Reserve for rivers. These techniques are largely based on the hydrological extrapolation of past IFR workshop results and are being continuously updated as more information becomes available. Two documents <Hydrological Extrapolation> and <Desktop DSS> are included on this web site and explain the background to these developments. Further information about the current status of the Desktop Reserve model can be found through the SPATSIM Help system (see the National Reserve Database link) or in the following journal publication.

Hughes, D A and Hannart, P (2003) A desktop model used to provide an initial estimate of the ecological instream flow requirements of rivers in South Africa. Journ. Hydrol., 270, 167-181.


Ecological Adjustments to the Hydrological Extrapolations

The initial developments referred to above have been based almost totally on the hydrological characteristics of rivers within South Africa and no account was taken of variations between rivers that are related to ecological conditions that are not directly connected to hydrological variation. A short term project was started in 1999 by Prof. Denis Hughes and Ms Frauke Münster (supported by the Water Research Commission) to investigate the possibility of identifying generic ecological factors that could be incorporated into the DSS to support the hydrological extrapolations and improve the confidence in the Reserve planning estimates. A document on this web site is available to describe the developments that resulted from this project. It became clear that this type of approach was unlikely to lead to real improvements and that further understanding of the links between hydrology and ecological functioning on a regional scale is required.

Ecological Stress relationships with flow

One of the often perceived problems with the methods available to set the quantity component of the Ecological Reserve for rivers (and other systems) is the lack of a unified approach to quantifying the ecological risk inherent in changing a rivers flow regime. The IWR has investigated possible ways in which this can be achieved using the concept of 'Stress' and linking stress-discharge relationships with time series of discharges under different management scenarios. The idea has led to the Flow-Stressor Response approach to setting the Reserve which is discussed in a 2004 Water Research Commission report.

Hughes, DA (Editor) (2004) SPATSIM: An integrating framework for ecological Reserve determinations and implementation. Incorporating water quality and quantity components for rivers. Report to the Water Research Commission.

Comprehensive DSS for the Reserve

It had been recognised that there were a lot of very different techniques used to establish an estimate for the Reserve and that these tended to vary depending on who was doing the work, at what confidence level the estimate was being made (from desktop to comprehensive reserve determination), for which system the estimate was being made (rivers, estuaries, wetlands, groundwater, etc.). The main point is that there were different approaches being used and many of them not well defined and certainly not well integrated. It had also been recognised that there is a need for a larger number of specialists who have been trained and are capable of carrying out Reserve determinations. To facilitate the training and to make the application of the wide range of tools somewhat more efficient, the IWR have cooperated with a variety of other groups in the development of the tools and road maps that are now an integral part of the SPATSIM system.

Water quality components of the ecological Reserve

In cooperation with other groups, the IWR has participated in the development of the methods for undertaking the water quality components of ecological Reserve determinations. Together with supporting routines for water quality data analyses, these methods have been incorporated into the SPATSIM system.

Last Modified: Mon, 24 Aug 2015 09:21:11 SAST