Assessment of a hydrodynamic water quality model, DUFLOW, for a winter rainfall river

[摘要] ENGLISH ABSTRACT: The Berg River is one of the largest rivers in the winter rainfall area of the Western Cape and is one ofthe most important water supply sources of the area. The Riviersonderend-Berg system needs to beexpanded in order to meet increasing water demands of the Greater Cape Town (GCT) region. Theimplementation of future schemes will remove additional fresh water from the Berg River main stem,which will give rise to increased nutrient levels and higher salinity in the water. A water qualityinformation system (WQIS) has been proposed to benefit the management of water resources, the flowquantity and the quality of the water. A part of this WQIS will be a water-quality simulation model thatcharacterizes the water quality situation and is able to predict water quality responses to futureimplementations, as well as simulate different scenarios that can be used for management purposes.The objective of this study is to represent the water quality situation of the Berg River in a simulationmodel by implementing, testing and verifying a water quality simulation model, and assembling ahydraulic and water quality database suitable to meet foregoing objectives.This study firstly examined the water quality variables of concern: pH, Total Dissolved Salts (TDS) andphosphates to develop an understanding of the water quality responses and causes of the main stem ofthe Berg River system.A thorough review of the available models has been undertaken in the light of certain selection criteria,before determining that DUFLOW would be an acceptable model for this study. The water qualityvariables that have been modelled are TDS, Phosphates as P04, Oxygen and Temperature. As nopredefined module simulating temperature, TDS and COD was included; these algorithms, describingthe processes of these water quality variables have been additionally coded. The coding was possible,as DUFLOW' s water quality module consists of an open structure. The predefined water quality modulewas simplified to only include the water quality process algorithms, for water quality variables wheredata was available. Unfortunately, phosphates were mainly simulated on advection, and the influenceof all the additional processes could not be assessed.All data gathering and preparation for the model had to be completed before commencing the model configuration. This included information on cross-sections, historical flow records, bridges and weirsfor the hydraulic component ofDUFLOW. For the water quality module, information on historical grabsamples has been obtained and 'infilled' to provide daily time series.To simulate the water quality in a river as accurately as possible, the flow simulation needs to beaccurate. Ungauged subcatchment runoff was added to the simulation model to improve thecorrespondence between the simulated and the measured flow. Calibration of the water quality part ofDUFLOW was completed by adjusting the different parameters after a sensitivity analysis. The modelwas verified by using a different time period than for the configuration, to ensure that an independentdata set has been used.After configuring, calibrating and verifying the model, the applicability of the model could be tested fordifferent scenario runs. Three scenarios were chosen according to real situations:• a short term effluent spill, with and without water releases from an upstream source (eitherSkuifraam Dam or Voëlvlei Dam);• the impact on the flow and water quality situation of the river when an upstream dam is built;• a long term management control scenario, that analyses load or concentration releases into theriver according to limitations upstream and downstream of the discharge location.The scenario analysis provides an opportunity to assess the applicability of DUFLOW to simulate realtime management and operational issues in a river and to aid in management decisions.

[发布机构] Stellenbosch University