14. REVIEW OF THE PROPOSED SEA-DSS IN THE LIGHT OF GÖRGENS (2001) GUIDELINES FOR WATER RESOURCES MODELLING PROCEDURES TO SUPPORT WATER MANAGEMENT INSTITUTIONS

 

 

A draft document by Professor Görgens entitled "Guidelines for water resources modelling procedures to support water management institutions" has been used to assess how the proposed SEA-DSS will potential fare against the guidelines laid out in the DWAF commissioned document. The objectives of the guidelines contained in the report include:

 

 

In this paper, crucial generic activities, information and modelling requirements for IWRM are listed and described. The objective of this section is to review the proposed SEA-DSS output against the generically required information as identified by Görgens (2001). The guidelines presented in the draft Görgens document were used as the final document had not been completed at the time of completing this report.

 

The outcomes of the review are presented in Table 6. It should be noted that a few additions have been made to the requirements as listed in the draft Görgens report (2001). The symbols U and W in the SEA-DSS column indicate that the proposed SEA-DSS will or will not be able to meet the relevant requirements listed in the Görgens report, respectively. The words UD are used to represent activities currently "Under Development" in the New ACRU model.

 

Table 6 Review of the proposed SEA-DSS in comparison to the Gorgens (2001) report

Hydrology Discipline

Generic Information Requirements & Model Capabilities

SEA-DSS (ACRU)

Comment

Process Hydrology

Historical Flow Series

U

Naturalized Flow Series

U

Denaturalized Flow Series

U

Stormflow (floods)

U

Baseflow (low flows)

U

Channel Transmission Losses

W

This functionality currently does not exist in ACRU, however can be included into the model relatively easily

Explicit Spatial Disaggregating

U

Catchment can be subdivided into smaller units

At Least Daily Time Step

U

Monthly and Daily time steps

Stochastic Flow Generation

Stochastic Sequences

W

As the ACRU model operates on a daily time-step, the generation of stochastic sequences distributed catchments is currently not feasible due to problems associated with the cross correlation of daily rainfall.

Operational Hydrology

System Yield

UD

Operating Rules & Curtailments

UD

Bulk Water Abstraction

U

IBTs

U

Return Flows

U

IFRs

UD

Quality Simulation

Average WQ Load & Chemical Constituents

UD

Water quality has not explicitly been included in the SEA-DSS. The potential DSS should be designed in such a way that water quality may be included into the operation of the DSS. This may require modifications to the ACRU model, or to the incorporation of other WQ models into the DSS

WQ Time Series

UD

WQ Sources

Point

W

Non-Point

U

Reservoir WQ Processes

W

Groundwater Simulation

Water Table Depth

U

These routines may require further augmentation and verification

Groundwater Recharge

U

Aquifer Yield

U

Baseflow Contribution

?

Deep Percolation Losses

?

Land Use / Management Impacts Assessment

Irrigation

U

SFRAs

U

Urbanization

U

Alien Vegetation

U

This routine may require further modification

Ecological Modelling

Reserve Determination

W

Aquatic Biotic Responses to Flow Changes

W

Estuary Processes

W

Soil Erosion Simulation

Sediment Yield

U

Sediment Transport

U

Sediment Deposition (Channel & Reservoir)

W

Social & Economic Modelling

Economic Values of Various Water Use Activities

U

The SEA DSS will include a simple economic analysis. Research may be required to further develop the DSSs ability to model socio-economic considerations

Impacts of Changes in Water Using Activities on Incomes and Social Welfare

U

Potential Impacts of Climate Change

Streamflow Time Series

U

Uses Downscaled GCM Output

The ACRU model is a core component of the proposed SEA DSS. The following review of the ACRU model has been made in the Görgens (2001) document:

 

ACRU is a multi-purpose and multi-level integrated physical-conceptual modelling system that can simulate streamflow, total evaporation, and land cover/management and abstraction impacts on water resources at a daily time step (Schulze, 1995). A "menubuilder" program controls input to the menu, where the user enters parameter or catchment related values, or uses defaults provided. The ACRU model uses multi-layer soil water budgeting. Streamflow is generated as stormflow and baseflow dependent upon the magnitude of daily rainfall in relation to dynamic soil water budgeting. Components of the soil water budget are integrated with modules in the ACRU system to simulate many other catchment components including irrigation requirements and sediment yield. Spatial variation of rainfall, soils and land cover is facilitated by operating the model in "distributed" mode, in which case the catchment to be modelled is sub-divided into sub-catchments. Within these sub-catchments, units of similar hydrological response, based largely on land use zones, are designated to facilitate simulation of land use changes. The model treats groundwater dynamics through a non-linear reservoir. The model allows riparian zones to be saturated from upland throughflow processes. The model requires a degree of calibration. ACRU is continually being upgraded and is currently being re-coded in object-oriented format with systems operating rule feed-back facilities

 

Görgens (2001) points out that the use of GIS and a relational database may be of great assistance to the users of such a system. As part of the SEA DSS, a scenario generator that operates in a GIS environment is being designed. The scenario generator will be used to draw information from a relational database. Results from completed simulations will be written back to the database. The seamless integration of the scenario generator in the GIS environment with the ACRU model and a relational database promises to add great value to the DSS, as scenarios can quickly, easily and transparently be generated, and displayed using this system.

 

The conclusion that may be made is that the proposed SEA DSS is consistent with most of the requirements laid down in the Görgens draft document. As mentioned in the review of the ACRU model above, the model is continually being updated. The guidelines that the model is currently not able to meet may be met in the future in as a result of further model developments.