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.

Magister Scientiae - MSc (Environ & Water Science) / Studies have shown that the primary origin of salinity in river flows of the Sandspruit in the Berg Catchment located in the Western Cape Province of South Africa was mainly a result of atmospheric deposition of salts. The salts are transported to rivers through surface runoff and subsurface flow (i.e. through flow and groundwater flow). The purpose of this study was to determine the contributions of subsurface and surface flows to the total flows in the Sandspruit, Berg Catchment. Three rain events were studied. Water samples for two rain events were analysed for environmental tracers ?18O, Silica or Silicon dioxide (SiO2), Calcium (Ca2+) and Magnesium (Mg2+). Tracers used for two component hydrograph separation were ?18O and SiO2. The tracers, Ca2+ and Mg2+, revealed inconsistent contributions of both subsurface flow and surface flow. Two component hydrograph separations indicated is that groundwater is the dominant contributor to flow, while surface runoff mainly contributes during the onset of the storm event. Groundwater response to precipitation input indicated that boreholes near the river have a quicker response than boreholes further away from the river. Boreholes nearer to the river also indicate higher water levels in response to precipitation, in comparison to boreholes further from the river.

Magister Scientiae - MSc (Environ & Water Science) / Studies have shown that the primary origin of salinity in river flows of the Sandspruit in the Berg Catchment located in the Western Cape Province of South Africa was mainly a result of atmospheric deposition of salts. The salts are transported to rivers through surface runoff and subsurface flow (i.e. through flow and groundwater flow). The purpose of this study was to determine the contributions of subsurface and surface flows to the total flows in the Sandspruit, Berg Catchment. Three rain events were studied. Water samples for two rain events were analysed for environmental tracers ?18O, Silica or Silicon dioxide (SiO2), Calcium (Ca2+) and Magnesium (Mg2+). Tracers used for two component hydrograph separation were ?18O and SiO2. The tracers, Ca2+ and Mg2+, revealed inconsistent contributions of both subsurface flow and surface flow. Two component hydrograph separations indicated is that groundwater is the dominant contributor to flow, while surface runoff mainly contributes during the onset of the storm event. Groundwater response to precipitation input indicated that boreholes near the river have a quicker response than boreholes further away from the river. Boreholes nearer to the river also indicate higher water levels in response to precipitation, in comparison to boreholes further from the river.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Gully erosion is a major environmental problem not only having direct influences on site but also indirect influences felt further down the catchment. Combating gully erosion has proven to be elusive due to the difficulty in finding the causal factors and developing mechanisms involved. Soil is the medium in which gully erosion occurs yet few research have investigated it as a driving factor behind gully development and those that have has done it in a very elementary way. The first aim of this project was to physically and chemically characterise and classify the discontinuous gully system at Malansdam to establish the relationship between landscape hydrology and geomorphologic gully development with a focus on control factors. This was done by field observations, physical measurements and spatial and hydrological analyses with a Geographical Information System (GIS). The Malansdam gully system was the first ever recorded Strahler stream order (SSO) 5 classical gully system with the most active region being in the upper reaches where a steeper slope is experienced. Although piping was observed the V-shape channels and SAR data from traditional wet analysis indicated runoff to be the dominant formation process. A duo of factors, consisting of one anthropogenic and one natural factor respectively, was found that the major control factors behind the gully formation. A unique anthropogenic factor that has never been published beforehand was found to be the anthropogenic driving factor namely the ploughed contour cultivation technique employed by the farmers in the Sandspruit catchment. The ploughed contours act as channels firstly collecting and secondly moving water that would have drained naturally downwards in the valley to one exit point in the gully system. This allows increased erosive energy because of the larger volumes of water entering one single point in the upper reaches of the gully system where a steeper slope is experienced. The driving factor in the natural group was determined to be weak soil structure due to an abundant amount of exchangeable Mg2+ cations occupying the exchange sites on the clay fraction. This would cause soil to disperse in the presence of water even with a low amount of exchangeable Na+. Combat methods would accordingly exist in the form of rectifying the soil structure and finding an alternative to the ploughed contour system currently employed, but also planting vegetation especially grass or wheat in the gully channels. The second aim of this project was to determine the capability of Near Infrared (NIR) spectrometry, with wavenumbers 12 500 – 4 000 cm-1, to predict indicators used in soil science to establish the dispersive nature of a soil. These indices included the Exchangeable Sodium Percentage (ESP), Sodium Absorption Ratio (SAR), Magnesium Saturation Percentage (MS%), Electrical Conductivity (EC), Potential Hydrogen (pH) as well as the four main exchangeable cations namely calcium (Ca2+), potassium (K+), sodium (Na+) and magnesium (Mg2+). Surface and subsurface soil samples were collected from active gully heads. These samples were minimally pre-processed thus only dried, milled and sieved. Thereafter it was subject to NIR analysis making use of the Bruker multi-purpose FT-NIR Analyser (MPA; Bruker Optik GmbH, Germany) with a spectral range of 12 500cm-1 to 4000cm-1 which is. Partial Least Square Regression (PLSR) models were built for each index and the exchangeable cations making use of QUANT 2 utility of OPUS 6.5 (MPA; Bruker Optik GmbH, Germany) software. Five different regrssion statistics namely the coefficient of determination (r2), Root Mean Square Error of Cross Validation (RMSECV), Ratio of Performance to Deviation (RPD), Bias and the Ratio of Performance of Quartiles (RPIQ) were used to assess the legitimacy of each PLSR model. Upon validation all the PLSR models performed in line with previously published work and in certain cases better. The only exception was MS% which would require further investigation. NIR thus possess the capability to predict a soil’s dispersive nature in a fast, reliable, inexpensive and non- destructive way, thus implying whether or not it contributes to gully erosion at a significant level or only minimally. / AFRIKAANSE OPSOMMING: Donga erosie is 'n groot omgewingsprobleem. Dit het nie net ‘n direkte invloed op die area waar dit geleë is nie, maar het ook ‘n indirekte invloed wat elders in die opvangsgebied ervaar word. Bekamping van donga erosie is moeisaam aangesien die faktore wat aanleiding gee tot die vorming en dryf daarvan moeilik is om te bepaal. Grond is die medium waarin erosie plaasvind, maar daar is nogtans steeds min navorsing wat grond ondersoek het as ‘n moontlike faktor aanleiding gee tot donga erosie. Die wat dit al wel ingesluit het, het dit slegs op n baie elemntêre manier ondersoek. Die eerste doel van hierdie projek was om die diskontinue donga stelsel fisies en chemise te karakteriseer en klassifiseer om soedoende die verhouding tussen die landskap hidrologie en geomorfologiese donga ontwikkeling te bepaal met n fokus op die faktore wat dit dryf. Dit was gedoen deur middel van observasies gedoen terwyl veldwerk uitgerig was, fisiese metings asook ruimtelike en hidrologiese analises deur gebruik te maak van n Geografiese Inligting Stelsel (GIS). Die klassieke Malansdam donga stelsel is ‘n Strahler stroomorde (SSO) van 5 toegeken en is die eerste een ooit wat dit behaal het. Die mees aktiefste area was in die bolope waar die steilste helling ervaar was. Alhoewel ondergrondse pyp formasie waargeneem was het die V-vormige donga kanale en SAR data van die tradisionele nat analise aangedui dat afloop die dominante vorming proses was. Daar was gevind dat 'n duo van faktore, wat bestaan uit een menslike en een natuurlike faktor onderskeidelik, die faktore was wat donga ontwikkeling in die area dryf. 'n Unieke menslike faktor wat nog nie vantevore gepubliseer is, was bevind as die menslike faktor wat aanleiding gee tot donga erosie. Hierdie faktor is die bewerkiingsmetode wat in die Sandspruit opvangsgebied gebruik word naamlik geploegde kontoerbewerking. Die geploegde kontoere tree op as kanale om eerstens water te versamel en tweedens om die vloeirigting daarvan te wysig. Water wat onder natuurlike toestande afwaarts sou dreineer tot in die vallei word vasgevang deur die kontoere en gekanaliseer na een invloei punt in die donga. Hierdie proses verhoog die erosiekrag van die water aangesien groter volumes by 'n enkele punt in die steiler bolope van die donga stelsel invloei. Die dryf faktor in die natuurlike groep was swak grond struktuur. Die oorsaak hiervan was die besetting van ‘n grootmaat uitruilbare Mg2+ katione op die uitruil plekke van die kleifraksie. Dit sou veroorsaak dat grond in die teenwoordigheid van water maklik sou dispergeer, selfs in die teenwoordigheid van 'n lae hoeveelheid uitruilbare Na+ katione. Metodes om donga erosie te bekamp sal dienooreenkomstig bestaan uit die herstel van die grondstruktuur en die toepassing van 'n alternatiewe gondbewerkings stelsel. Die aanplanting van plantegroei, veral gras en koring binne die donga kanale sal verder help met die veg tot bekamping Die tweede doel van hierdie projek was om te bepaal indien naby infrarooi (NIR) spektrometrie (met golfnommer van 12 500 – 4 000cm-1) oor die vermoë beskik om aanwysers wat traditioneel in grondkunde gebruik word om die dispergering van grond te meet te voorspel. Hierdie aanwysers sluit vyf indekse in naamlik die Veranderlike Natrium Persentasie (ESP), Natrium Absorpsie Verhouding (SAR), Magnesium Versadiging Persentasie (MS%), Elektriese Geleidingsvermoë (EC) en die Potensiële Waterstof (pH) sowel as die vier hoof uitruilbare katione naamlik kalsium (Ca2+) , kalium (K+), natrium (Na+) en magnesium (Mg2+). Oppervlak en ondergrondse grondmonsters is ingesamel by die punt van oorsprong by aktiewe dongas. Hierdie monsters is minimaal voorberei, dus slegs gedroog, gemaal en gesif. Daarna was dit onderworpe aan die NIR analise. Die Bruker meerdoelige FT-NIR Analiseerder (MPA; Bruker Optik GmbH, Duitsland) met 'n spektrale omvang van 12 500cm 1 4000cm-1 is hiervoor gebruik. Parsiële kleinste kwadraat regressie (PLSR) modelle is gebou vir elke indeks asook die uitruilbare katione deur gebruik te maak van die nutsprogram Quant 2 van die OPUS 6.5 (MPA; Bruker Optik GmbH, Duitsland) sagteware. Vyf verskillende regressie statistieke naamlik die bepalingskoëffisiënt (r2), vierkantswortel fout tydens kruis validasie (RMSECV), verhouding van prestasie teenoor voorspellingsafwyking (RPD), sydigheid en die verhouding van prestasie van kwartiele (RPIQ) was gebruik om die geldighied van elke PLSR model te asseseer. Alle PLSR modelle het goed presteer, behalwe vir MS% wat verdere navorsing vereis. NIR beskik dus oor die vermoë om die aard van dispergering van grond te bepaal op 'n vinnige, betroubare, goedkoop en nie afbrekende manier. Dit kan dus effektief aangewend word as ‘n substitusie vir die traditionele metodes om te bepaal as grond a beduidende faktor is of nie.

The Sandspruit River catchment, found within the heart of the Swartland region is infamous for wheat and wine production. Variable groundwater quality and low productivity is encountered within the folded and fractured Malmesbury Group aquifer, whilst the most productive and better quality groundwater is found within the Table Mountain Group sandstone. The Sandspruit catchment (a tributary of the Berg River) represents a drainage system, whereby saline groundwater with TDS up to 10870 mg/l, and EC up to 2140 mS/m has been documented. The catchment belongs to the winter rainfall region with precipitation seldom exceeding 400mm/yr, as such, groundwater recharge occurs predominantly from May to August. Recharge estimation using the catchment water-balance method, chloride mass balance method, and qualified guesses produced recharge rates between 8-70 mm/yr. To understand the origin, occurrence and dynamics of the saline groundwater, a coupled analysis of major ion hydrochemistry and environmental isotopes (δ¹⁸O, δ²H and ³H) data supported by conventional hydrogeological information has been undertaken. Research data were collected in three seasonal field sampling campaigns within the study catchment. These spatial and multi-temporal hydrochemical and environmental isotope data provided insight into the origin, mechanisms and spatial evolution of the groundwater salinity. These data also illustrate that the saline groundwater within the catchment can be attributed to the combined effects of evaporation, salt dissolution, and groundwater mixing. The geology together with the local and regional faults control the chemistry of the groundwater, whereby relatively fresh groundwater can be observed in certain direct recharge areas. The salinity of the groundwater tends to vary seasonally and evolves in the direction of groundwater flow. The stable isotope signatures further indicate two possible mechanisms of recharge; namely, (1) a slow diffuse type modern recharge through a relatively low permeability material as explained by heavy isotope signal and (2) a relatively quick recharge prior to evaporation from a distant high altitude source as explained by the relatively depleted isotopic signal and sub-modern to old tritium values. A conceptual hydrogeological model based on the hydrogeological, hydrochemical, and environmental isotope data was developed for the Sandspruit catchment. This model, together with statistical and groundwater quality analysis has lead to the development of a proposed local optimized monitoring scheme for the catchment. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.