Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008. / In recent years, concern about the water quality in the Berg River received a fair degree of attention, particularly with the imminent construction of the Berg Water Project (BWP). Particular concerns have been expressed about the water quality with respect to total dissolved salts (TDS) at Misverstand Dam. In previous studies (Fourie and Görgens, 1977) it was identified that the saline water was mostly generated in the lower portion of the Berg River Catchment (Matjies, Moorreesburg and Sandspruit Rivers) and that the abstraction of acceptable quality water higher up in the Berg River could possibly result in salinity problems at Misverstand Dam. Contrary to expectation, these studies also showed that for the most saline catchments, a winter peak in TDS concentrations also existed. To help address these concerns, a Water Research Commission (WRC) project was initiated in 2003 in which the newly-developed salinity module of the daily Agricultural Catchment Research Unit (ACRU) agrohydrological model, known as ACRUSalinity, would be configured for the Berg River Catchment. This model had previously been configured and calibrated for the Mkhomazi Catchment (Teweldebrhan, 2003) which exhibited relatively low streamflow TDS concentrations (100 mg/l) and it was deemed necessary to ascertain whether comparable TDS values could be simulated in the Berg River Catchment, where TDS concentration could rise to well above 1 000 mg/l in certain tributaries. In this project, ACRUSalinity was configured for the Berg River Catchment on a distributed basis, aiming to capture the spatial distribution of rainfall and geophysical characteristics which inherently exist in a catchment as expansive as the Berg. Initial application of the "Beta version" of ACRUSalinity to the Berg River Catchment revealed that it failed to produce simulated TDS values which were representative of the observed data. It became evident that the model required both additional salinity-related functions and modifications of existing functions. After the implementation of these algorithm changes the correspondence of simulated and observed TDS concentrations improved markedly. Verification of the ACRUSalinity simulated flows and calibration of the salinity-related parameters was based on the values of predefined objective functions. Reasonably representative flows could be obtained provided that the catchment discretisation and driver rainfall selection process were adequate. Salinity related parameters were determined purely on an iterative basis, although a priori estimation of these parameters was possible. Preliminary interdependency tests of these parameters revealed that the final calibrated set of salinity-related parameters was probably not unique and that some a priori decision making would be required when selecting the most realistic set of parameters. Quantification of the potential effect of the Berg River Dam on the TDS concentrations at Misverstand Dam was achieved as follows: the ACRUSalinity model was verified for flow and calibrated for TDS at available and reliable flow gauging stations. This was then followed by a long-term simulation run which yielded daily TDS time series for comparison, on an exceedance basis, with the observed record. Since the concern about the possible deterioration of water quality at Misverstand Dam was only a winter concern (May to September), comparisons were only drawn over this period. The flow-routing option in ACRUSalinity was not activated and a 1:1 daily comparison of flows and TDS concentrations, based on values of the objective function, was thus not possible. Results from this study showed that even with a daily model, the exceedance percentages of the TDS concentrations after the construction of the Berg River Dam were comparable with the exceedance percentages obtained from the original monthly modelling study (DWAF, 1993). In this study, however, it was possible to capture the increasing TDS concentration which was evident over winter months in the observed data record for the Matjies River and Sandspruit River catchments. The testing of the model’s effectiveness in the evaluation of engineering options was accomplished as follows: several options for ameliorating the possible deterioration of water quality at Misverstand Dam were defined, based on its practicality and cost of implementation. For example, the Withoogte water treatment works abstracts water from Misverstand Dam for supply to the West Coast region when water quality is acceptable (i.e. a TDS lower than 450 mg/l). It was proposed that to minimise the effect of periods when no abstraction from Misverstand could occur due to unacceptable water quality, a second reservoir at the treatment works should be lined and used to provide bridging storage for water from Misverstand Dam when the water quality was acceptable. The calibrated ACRUSalinity model was then modified to reflect the physical attributes of this engineering scenario of interest to produce sets of flow and TDS time series which could be further analysed to determine assurance of supply, in terms of predetermined TDS concentration thresholds in Misverstand Dam. Using this particular engineering option, the analysis revealed that a 300 mg/l TDS upper-limit at Misverstand was too stringent and that 450 mg/l was probably more realistic.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Bugan, R.D.H. Modelling and regulating hydrosalinity dynamics in the Sandspruit River catchment (Western Cape). PhD dissertation, Stellenbosch University. The presence and impacts of dryland salinity are increasingly become evident in the semi-arid Western Cape. This may have serious consequences for a region which has already been classified as water scarce. This dissertation is a first attempt at providing a methodology for regulating the hydrosalinity dynamics in a catchment affected by dryland salinity, i.e. the Sandspruit catchment, through the use of a distributed hydrological model. It documents the entire hydrological modelling process, i.e. the progression from data collection to model application. A review of previous work has revealed that salinisation is a result of land use change from perennial indigenous deep rooted vegetation to annual shallow rooted cropping systems. This has altered the water and salinity dynamics in the catchment resulting in the mobilisation of stored salts and subsequently the salinisation of land and water resources. The identification of dryland salinity mitigation measures requires thorough knowledge of the water and salinity dynamics of the study area. A detailed water balance and conceptual flow model was calculated and developed for the Sandspruit catchment. The annual streamflow and precipitation ranged between 0.026 mm a-1 - 75.401 mm a-1 and 351 and 655 mm a-1 (averaging at 473 mm a- 1), respectively. Evapotranspiration was found to be the dominant component of the water balance, as it comprises, on average, 94% of precipitation. Streamflow is interpreted to be driven by quickflow, i.e. overland flow and interflow, with minimal contribution from groundwater. Quantification of the catchment scale salinity fluxes indicated the Sandspruit catchment is in a state of salt depletion, i.e. salt output exceeds salt input. The total salt input to and output from the Sandspruit catchment ranged between 2 261 - 3 684 t Catchment-1 and 12 671 t a-1 - 21 409 t a-1, respectively. Knowledge of the spatial distribution of salt storage is essential for identifying target areas to implement mitigation measures. A correlation between the salinity of sediment samples collected during borehole drilling and the groundwater EC (r2 = 0.75) allowed for the point data of salt storage to be interpolated. Interpolated salt storage ranged between 3 t ha-1 and 674 t ha-1, exhibiting generally increasing storage with decreasing ground elevation. The quantified water and salinity fluxes formed the basis for the application of the JAMS/J2000-NaCl hydrological model in the Sandspruit catchment. The model was able to adequately simulate the hydrology of the catchment, exhibiting a daily Nash-Sutcliffe Efficiency of 0.61. The simulated and observed salt outputs exhibited discrepancies at daily scale but were comparable at an annual scale. Recharge control, through the introduction of deep rooted perennial species, has been identified as the dominant measure to mitigate the impacts of dryland salinity. The effect of various land use change scenarios on the catchment hydrosalinity balance was evaluated with the JAMS/J2000-NaCl model. The simulated hydrosalinity balance exhibited sensitivity to land use change, with rooting depth being the main factor, and the spatial distribution of vegetation. Revegetation with Mixed forests, Evergreen forests and Range Brush were most effective in reducing salt leaching, when the “salinity hotspots” were targeted for re-vegetation (Scenario 3). This re-vegetation strategy resulted in an almost 50% reduction in catchment salt output. Overall, the results of the scenario simulations provided evidence for the consideration of re-vegetation strategies as a dryland salinity mitigation measure in the Sandspruit catchment. The importance of a targeted approach was also highlighted, i.e. mitigation measures should be implemented in areas which exhibit a high salt storage. / AFRIKAANSE OPSOMMING: Die teenwoordigheid en impak van droëland versouting word duideliker in die halfdor Wes-Kaap. Dit kan ernstige gevolge inhou vir die streek wat reeds as ‘n waterskaars area geklassifiseer is. Hierdie verhandeling is ‘n poging om ‘n metode vir die regulering van waterversoutingsdinamiek in ‘n opvangsgebied wat deur verbrakking van grond geaffekteer is, i.e. die Sandspruit opvangsgebied, te bepaal deur gebruik te maak van ‘n verspreide hidrologiese model. Dit dokumenteer die volledige hidrologiese modeleringsproses, i.e. vanaf die versameling van data tot die aanwending van die model. ‘n Oorsig van vorige studies bevestig dat versouting ‘n gevolg is van die verandering vanaf meerjarige inheemse plantegroei met diep wortelstelsels tot die verbouing van gewasse met vlak wortelstelsels. Dit het ‘n verandering in die water en versoutingsdinamiek in die opvangsgebied tot gevolg gehad in soverre dat dit die mobilisering van versamelde soute en gevolglike versouting van die grond en waterbronne tot gevolg gehad het. Die identifikasie van maatreëls om droëland versouting te verminder, vereis ‘n deeglike kennis van die water- en versoutingsdinamiek van die studie gebied. ‘n Gedetailleerde waterbalans en konseptuele vloeimodel was bereken vir die Sandspruit opvangsgebied. Die jaarlikse stroomvloei en neerslag varieer tussen 0.026 - 75.401 mm a-1 en 351 - 655 mm a-1 (gemiddeld 473 mm a-1), onderskeidelik. Dit is bevind dat evapotranspirasie die dominante komponent is van die waterbalans, aangesien dit 94% uitmaak van die neerslag. Stroomvloei word aangedryf deur snelvloei, i.e oppervlakvloei en deurvloei met minimale bydrae van grondwater. Die omvang van die opvangsgebied se soutgehalte het aangedui dat die Sandspruit opvangsgebied tans ‘n toestand van soutvermindering ondervind, i.e. sout invloei word oorskrei deur sout uitvloei. Die totale sout in- en uitvloei in die Sandspruit opvangsgebied het gewissel tussen 2 261 - 3 684 t Opvangsgebied-1 en 12 671 - 21 409 t a-1 onderskeidelik. Kennis van die ruimtelike verspreiding van opbou van soute in die grond is belangrik om areas te identifiseer vir die toepassing van voorsorgmaatreëls. ‘n Korrelasie tussen die soutinhoud van sediment monsters wat versamel is tydens die boor van boorgate en die grondwater EC (r2 = 0.75) het die interpolasie van puntdata waar sout aansamel toegelaat. Hierdie interpolasie van sout aansameling het gewissel tussen 3 t ha-1 and 674 t ha-1 en bewys ‘n algemeen verhoogde opbou met vermindering in grond elevasie. Die hoeveelheidsbepaling van water en die versoutings roetering vorm die basis vir die aanwending van die JAMS/J2000-NaCl hidrologiese model in die Sandspruit opvangsgebied. Die model het ‘n geskikte simulasie van die hidrologie van die opvangsgebied geimplimenteer, en het ‘n daaglikse Nash-Sutcliffe Efficiency van 0.61 getoon. Die gesimuleerde en waargenome sout afvoer het teenstrydighede getoon t.o.v daaglike metings maar was verenigbaar op ‘n jaarlikse skaal. Aanvullingsbeheer deur die aanplanting van meerjarige spesies met diep wortelstelsels is geidentifiseer as ‘n oorwegende maatreël om die impak van verbrakking van grond teë te werk. Die effek van verskeie veranderde grondgebuike op die balans van die opvangsgebied se hidro-soutgehalte is geëvalueer met die JAMS/J2000-NaCl model. Die balans van gesimuleerde hidro-saliniteit het ‘n sensitiwiteit t.o.v veranderde grondgebruik getoon, met die diepte van wortelstels as die hoof faktor, asook die ruimtelike verspreiding van plantegroei. Hervestiging van verskeie tipes bome, meerjarige bome en “Range Brush” was die effektiefste t.o.v die vermindering in sout uitloging waar die soutgraad konsentrasie areas ge-oormerk was vir hervestiging van plantegroei (Scenario 3). Die strategie van hervestinging het ‘n afname van 50% in versouting in die opvangsgebied getoon. In die geheel het die resultate van die simulasies genoegsame bewys gelewer dat ‘n strategie van hervestiging en groei as ‘n voorsorg maatreël kan dien om droëland versouting in die Sandspruit opvangsgebied teen te werk. Die belangrikeid daarvan om ‘n geteikende benadering te volg is benadruk, i.e. voorsorg maatreëls kan toegepas word in areas met hoë soutgehalte.