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Doctor of Philosophy / Department of Biology / Walter K. Dodds / Streams exist in a state of dynamic equilibrium with frequent floods and drought. The frequency and intensity of stream disturbances are projected to increase with greater water withdrawal for agriculture and biofuel production, watershed development, and altered climate. Changes in the hydrologic regime may alter stream ecosystems. I studied how stream communities return after disturbances and how nutrients, consumers, and substrata heterogeneity influence recovery trajectories. Large consumers were excluded from pools following a severe drought to assess how community structure and function returned in their absence. Large consumers reduced algal biomass, primary productivity, and nutrient uptake rates, and delayed macroinvertebrate recolonization. However, grazer effects were temporary and their influence weakened after five weeks. In a second experiment, I assessed the relative influence of grazer density and nutrient loadings on algal recovery from flood. Nutrients had a stronger effect on recovery than grazers, but the strength of each varied temporally. Grazer control decreased and nutrient control increased over time. A third experiment addressed the physical properties of stream substrata on algal development. The relationship among algal accumulation and substrata surface topography was assessed by growing algae on substrata with varying orientation and roughness. Total algal biomass decreased on surfaces with angles > 45 degrees, and peaked at an intermediate roughness (pit depth of [similar to]17 [Mu]m). Rougher surfaces collected more tightly attached (grazer resistant) forms and less loosely attached (grazer susceptible) forms. Individual algal forms responded differently to grazing pressure, nutrient availability, and surface features. I developed a method using Fourier-transform infrared microspectroscopy to measure single-cell physiological responses in benthic algae. Nutrients and consumers were strong regulators of ecosystem succession following disturbance, but nutrient influence was stronger. The influence of nutrients and consumers were context dependent, and changed over the course of recovery. Rougher surfaces increase algal growth and shifted algal assemblages to more grazer resistant forms, which may decrease the influence of large consumers on stream function. Altering the severity and frequency of disturbances can change the trajectory of stream recovery and ultimately change community composition and stream metabolic activity, which may alter ecosystem services such as water purification and recreation.

Over recent years, community resilience has been increasing in popularity as a topic for detailed study. During that time, academic researchers have been working to untangle the complex network of social relationships that define the concept. In parallel, some institutions have set the achievement of enhanced community resilience as a policy goal. This research has sought to assist in both areas: first, by contributing to the academic debate and second, to build a clearer understanding of how institutions can tailor policies to ensure success in their goal of enhancing community resilience. A case study approach was adopted for the research, centring on three communities in the Teign Estuary of South Devon (Newton Abbot, Teignmouth and Shaldon). All three communities were vulnerable to tidal flooding and links between the communities and institutions responsible for managing flood risk (FRM framework) were analysed. In the analysis, a specific form of social capital was studied: social capital derived from community-institution links (CISC). CISC was found to be effective in revealing links with the greatest potential to enhance the resilience of communities against flood risks. To assess resilience at the individual and community level, a maturity based model was used. The assessment found disparities between how resilience matures at the community level compared to the individual level. Specifically, resilience maturity in communities was revealed as a less linear process. As such, the case study communities were able to exhibit traits associated with low resilience maturity at the same time as exhibiting traits associated with high resilience maturity. This research concluded that the UK FRM policy framework was robust, aligning well with academic theory. However, the FRM system was revealed as being dominated by expert elites. These elites are mainly public sector based and were judged to be stifling the engagement of the private sector at the local level. To enhance their resilience, this study determined that communities need to investment in CISC, but that investment must not just be targeted at public sector FRM institutions alone, it also needs to target private sector FRM institutions.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In the context of rapidly expanding cities, it is imperative that urban planning in South Africa has sufficient guidance regarding stormwater and river corridor management, in order to provide solutions that address issues of flood risk and the environmental health of river systems. Attenuation of stormwater runoff, the focus of this study, is one of the most important structural mechanisms used for the mitigation of many of the negative impacts caused by uncontrolled urban runoff. Typically, it involves the use of attenuation ponds or wetlands, which temporarily store runoff during a storm and release flow downstream at a reduced rate so as to mimic natural flow patterns. The focus of urban stormwater management and flood control has historically been on the protection of human life and property. However, in recent decades, through growing environmental awareness and the advancement of the concept of sustainable development, urban stormwater management has become a growing field of research worldwide, with a broader focus which considers not only flood control, but also water quality, aquatic biodiversity and the amenity value of urban drainage systems. Flood attenuation controls are becoming more widely used within South African urban areas, primarily due to policies or legislation brought into effect by local authorities. However, there is often little understanding regarding the positive and perhaps negative effects that these attenuation controls are having on receiving watercourses downstream. Three case studies were assessed by means of stormwater modelling simulations to evaluate various flood attenuation practices which are currently in use in South Africa. Two of the study areas, the Mosselbank River Catchment and the Bayside Canal Catchment, were selected in areas of Cape Town where future development has been proposed by spatial planners. The third study area, the Upper Kuils River Catchment, was evaluated in terms of the performance of existing attenuation facilities in an area which is already almost completely developed. The study found that attenuation facilities constructed with a single culvert-type outlet structure, designed to reduce flows during large storm events, do not mitigate the impact of post-development runoff occurring during lower recurrence interval storm events. Attenuation facilities with multi-stage outlet structures were found to be much more effective at mimicking pre-development flow during a range of storm events. It was also found that because attenuation does not reduce post-development runoff volumes to pre-development levels, but merely reduces peak flow rates, the cumulative runoff from multiple attenuation controls across a large (>30 km2) urban catchment resulted in higher runoff peaks in downstream watercourses. The study concluded that more widespread use of stormwater Best Management Practices (BMPs) and Sustainable Drainage System (SuDS) controls allows a greater portion of runoff to infiltrate, resulting in less runoff volume and therefore reduced peak flows downstream, especially during low recurrence interval storm events. In addition, the study recommended the use of detailed catchment-wide stormwater modelling to understand specific catchment dynamics holistically, thus increasing the potential for designing effective attenuation controls in urban stormwater systems. / AFRIKAANSE OPSOMMING: In die konteks van die vinnige tempo van stedelike uitbreiding, is dit noodsaaklik dat stedelike beplanning in Suid-Afrika plaasvind met in aggenome van voldoende riglyne vir die bestuur van stormwater en rivierkorridors, ten einde oplossings te vind vir die kwessies van vloedrisiko en die omgewingsgesondheid van rivierstelsels. Vloedvertraging, wat die fokus van hierdie studie is, is een van die belangrikste strukturele meganismes wat gebruik word vir die verligting van talle negatiewe impakte wat veroorsaak word deur onbeheerde stormwaterafloop in stedelike gebiede. Tipies behels dit die gebruik van vloedvertragingsdamme of vleilande, wat afloop vertraag tydens 'n storm en dus vloei stroom-af teen 'n verlaagde tempo uitlaat met die doel om natuurlike vloeipatrone na te boots. Die fokus van stedelike stormwaterbestuur en vloedbeheer was in die verlede hoofsaaklik op die beskerming van lewe en eiendom gefokus, maar het egter die afgelope dekades verskuif na water gehalte, die biodiversiteit van waterekosisteme en die geriefswaarde van stedelike dreineringstelsels. Hierdie verskuiwing van fokus is weens die groeiende omgewingsbewustheid en die bevordering van die konsep van volhoubare ontwikkeling wat wêreldwyd 'n groter navorsingsgebied geraak het. Vloedvertraging beheermeganismes word al hoe meer algemeen gebruik in Suid-Afrikaanse stedelike gebiede, hoofsaaklik as gevolg van die beleide of wetgewing wat deur plaaslike owerhede in werking gestel is. Daar is egter dikwels min begrip vir die positiewe en moontlike negatiewe gevolge wat hierdie vertragingsmeganismes op stroom-af sisteme het. Drie gevallestudies is geëvalueer deur middel van numeriese modelstudies wat verskeie benaderings van vloed beheer, wat tans in Suid-Afrika gebruik is, in ag neem. Twee van die studie areas, naamlik die Mosselbank en die Bayside-kanaal opvanggebiede in die Kaapse metropool, is gekies in areas waar toekomstige ontwikkeling in die vooruitsig gestel is deur stadsbeplanners. Die derde studie area, die opvangsgebied van die bolope van die Kuilsrivier, is in terme van die prestasie van bestaande stormwater infrastruktuur in 'n gebied wat reeds byna heeltemal ontwikkel is, geëvalueer. Die studie het bevind dat vloedvertragingsfasiliteite met 'n enkele duiker uitlaatstruktuur, wat ontwerp is met die doel om die vloeispitse tydens groot storms te demp, nie die impak van die na-ontwikkeling afloop, wat gedurende storms met laer herhalingsinterval voorkom, verminder nie. In terme van vloedvertragingsfasiliteite met 'n veelvuldige uitlaatstruktuur, is dit bevind dat voorontwikkelingsafloop tydens 'n reeks van groot en kleiner storms veel meer effektief nageboots word. Daar is egter ook bevind dat die demping van die vloedspitse nie die naontwikkeling afloopvolumes verminder tot voorontwikkelingsvlakke nie, maar slegs tot die vermindering van maksimum snelhede lei. Die gevolg is dat die totale afloop van ‘n kombinasie van ‘n aantal vertragingsdamme oor 'n groot (> 30 km2) stedelike opvanggebied ‘n hoër spitsvloei in die stroom-af riviere tot gevolg het. Die studie het bevind dat die wydverspreide gebruik van bestebestuurspraktyke (BMPs) en volhoubare stedelike dreineringstelsels (SuDS) tot die infiltrasie van ‘n groter gedeelte van die afloop lei, wat laer afloopvolume en dus verminderde spitsvloei stroomaf tot gevolg het, veral gedurende storms met ‘n lae herhalingsinterval. Daarbenewens word die aanwending van gedetailleerde modellering van stormwatersisteme binne die groter opvangsgebied aanbeveel ten einde ‘n meer holistiese begrip van spesifieke aspekte van die opvangegebied dinamika, om sodoende die potensiaal vir die ontwerp van effektiewe vloedvertragingskontroles in stedelike stormwaterstelsels te verbeter.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Global warming will result in a sea level rise of between 0.25 and 0.82 m by 2090, as well as an increase in intensity and frequency of both extreme sea level and extreme rainfall events. In consequence, low-lying areas will be permanently inundated, extreme waves will penetrate further inland and flood intensity and frequency will increase. Estuaries are subject to the effect of both extreme sea levels and extreme floods and water levels in estuaries are expected to increase, under both open and closed conditions. As a response to expected higher flood levels, setback lines have been legislated in South Africa. For cases where a flood level study has not been undertaken, a minimum setback line at the 5 m above mean sea level (MSL) contour is prescribed in terms of the National Environmental Management Act (Act 107 of 1998). This study assessed the adequacy of the 5 m setback line, under the effects of climate change, for Great Brak estuary. Local features of the Great Brak estuary may influence flood levels. Specifically, the lagoon of the Great Brak estuary, below the N2 Bridge, is small at 1.1 x 0.7 km. Further, it is constrained at the upstream end by road and rail embankment, and on the left bank by steep slopes. A sand barrier at the mouth is at times breached, both naturally and artificially. Artificial breaching is initiated when the sand barrier is between 1.5 and 2.0 m high, or when a flood is forecast. The barrier has previously reached 2.7 m, higher than the still water level of the sea, which has not exceeded 2 m above MSL. There is a populated island about 180 m upstream of the mouth. The greater extent of the island is below 2.5 m above MSL. Mike11 software was used to generate flood levels on which the conclusions of this study are based. The study determined that the influence of the increased sea levels does not extend much beyond the N2 Bridge. This may be a peculiarity of the Great Brak estuary, due to the influence of the three bridges and the road and rail embankments. For the scenario where Mean High Water Springs coincides a with an extreme sea storm and there is a 100-year riverine flood, the flood level in the estuary is 3.16 m at the mouth, increasing to 4 m upstream of the N2 bridge. In the scenario where the barrier height was raised to 4 m above MSL, the flood levels were 4.52 m downstream of, and 5 m upstream of, the N2 Bridge. Extensive inundation of properties in the floodplain and on the Island will occur, as well as the inundation of the N2 embankment. The probability of such an extreme sea level event occurring at the same time as peak runoff of a 100-year riverine flood is unlikely. It is the conclusion of this study that, for the Great Brak River, the 5 m setback line, as prescribed, is sufficient for an extreme situation where a future 100-year flood coincides with the MHWS coincides and an extreme sea storm raising the sea level to 2.65 above current MSL. / AFRIKAANSE OPSOMMING: Aardverwarming sal lei tot 'n styging van seevlakke van tussen 0.25 en 0.82 m teen 2090, sowel as 'n toename in intensiteit en frekwensie van beide stormseevlak en reënval. Gevolglik sal laagliggende gebiede permanent oorval word, stormgolwe verder in die binneland dring en vloed intensiteit en frekwensie toeneem. Riviermondings is onderhewig aan die effek van beide hoë seevlakke en vloede. Om die negtaiewe effekte van hoër vloedvalktes te bekamp word ‘n minimum terugsetlyn van 5 m bo seevlak voorgeskryf, in terme van die Wet op Nationale Omgewingsbestuur (Wet 107 van 1998). Hierdie is van toepassing waar ‘n vloedlyn studie nie onderneem is nie. Hierdie studie beoordeel die geskiktheid van die 5 m terugsetlyn, onder die invloed van klimaatsverandering, vir Groot Brak rivier monding. Plaaslike kenmerke van die Groot Brak monding mag vloed vlakke beïnvloed. Spesifiek, die Groot Brak monding meer het ‘n oppervak van net 1,1 x 0,7 km; is in die stroomop rigting beperk deur pad en spoor walle; en word op linkeroewer deur steil hellings vesper. Die sandversperring by die word kunsmatig oopgemmak wanneer die sand versperring tussen 1,5 en 2,0 m hoog is, of wanneer 'n vloed voorspel word. Hierdie sandversperring het al voorheen 2.7 m hoogte beriek, hoër as die 2 m maksimum historiese stilwater vlak van die seë. Daar is 'n bevolkde eiland sowat 180 m stroomop van die mond. Die die eiland is meestelik onder 2.5 m bo seevlak. Mike11 sagteware is gebruik om vloed vlakke, waarop die bevindinge van hierdie studie gebaseer is, te bepaal. Hiedie studie bevind dat die effek hoër voedvlakke trek nie veel verder stroomop as die N2 brug, oontlike weens die voorkoms van die drie bruë. In die geval waar ‘n uiterste seëstorm terselfde tyd voorkon as die lente hoogwater gety endie 100 jaar river vloed, sal die watervlak in the mondingsmeer tot 3.16 m bo huidiglike seëvlak styg by die mond, en tot 4 m bo huidiglike seëvlak by die N2 brug. In die geval waar die sandversperring by the riviersmond 4 m verhoog is, sal die watervlak in the mondingsmeer tot 4.5 m bo huidiglike seëvlak styg by die mond, en tot 5 m bo huidiglike seëvlak by die N2 brug. Faktore nie in ag geneem in hierdie studie sluit in die uitwerking van die verhoogde afloop, sediment verandering en die effek van windgolwe oor die ondingsmeer. Wydverspreide vloeding van ontwikkelde areas aangrensend to vloedvlakte sal voorkom, insluitend die oorstroing van die N2 padwal. Die waarskynlikheid is klein dat ‘n uiterste seëstorm terselfde tyd voorkom as the lengte hoogwater gety en die 100 yaar rivier vloed. Dit is dus die gevolgtrekking van hierdie studie dat die 5 m terugsetlyn soos voorgeskryf, voldoende is vir Groot Brak rivier vir so ‘n uiterste geval.

published_or_final_version / Real Estate and Construction / Master / Master of Science in Construction Project Management

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Shallowly-buried channel systems have been imaged on the New Jersey Shelf with high-resolution seismic imaging. These channels formed as riverine systems that occupied the exposed shelf during the Last Glacial Maximum, ~18 ka. Subsequent sea level rise ~15-12 ka modified the valleys, forming estuaries and filling the channels with estuarine sediments. The infill sediments within the channel provide evidence for the response of the shelf to the Late Pleistocene glacio-eustatic sea level rise, but little work has been done on samples from these strata. This study aids in the ground-truthing of previous stratigraphic results by analyzing the cores collected within the infill sediments. The seismic stratigraphy of fill sediments from the mid-shelf and outer-shelf channels are structurally dissimilar. The mid-shelf channel fill stratigraphy is dominated by finely-laminated U-shaped reflectors throughout the section, with cut and fill geometries. In contrast, the outer shelf channel fill stratigraphy is a well-ordered sequence of 4 identifiable, primarily flat-lying seismic units. We collected five cores in mid-shelf channels (~30 m water depth), one in an outer shelf channel (~80 m of water depth) and one core in the trangressive ravinement surface. Cores were logged for density and seismic velocity. Grain size analysis was conducted by settling column and laser particle size analyzer. Radiocarbon analysis of the stratigraphy was conducted with the shell fragments and organic mud within the samples. The foraminiferal assemblages aided in determining the depositional environment. Using these data I investigated the differences in depositional environment of the mid- and outer-shelf channels systems, and consider these results in the context of sedimentary models for estuarine processes. The radiocarbon dates and foraminiferal are consistent with channel infill in an estuarine environment. Grain size and density log data indicate that the mid-shelf channel fills are sandier than the outer-shelf channel fills, which leads me to infer that the sediment from the mid-shelf channels was deposited in a higher energy environment than that of the sediment in the outer shelf channels. The stratigraphic differences and locations of the channel systems are similar to the Zaitlin (1994) model of incised valley infill, but infill of the mid-shelf channel system could possibly be the result of a catastrophic meltwater flood event occurring ~14 ka as glacial lakes to the north broke their dams and flooded the mid-shelf. / text

Glacial-dominated areas pose unique challenges to downstream communities in adapting to recent and continuing global climate change, including increased threats of glacial lake outburst floods (GLOFs) that have substantial impacts on regional social, environmental and economic systems increasing risk due to flooding of downstream communities. In this dissertation, two lakes with potential to generate GLOFs were studied, Imja Lake in Nepal and Palcacocha Lake in Peru. At Imja Lake, basic data was generated that allowed the creation of a conceptual model of the lake. Ground penetrating radar and bathymetric surveys were performed. Also, an inundation model was developed in order to evaluate the effectiveness of a project that seeks to reduce flooding risk by lowering the lake at least 3 meters. In Peru, a GLOF inundation model was created. Also, the vulnerability of the people living downstream in the City of Huaraz was calculated, and the impacts of an early warning system were evaluated. The results at Imja indicated that the lake deepened from 98 m in 2002 to 116 m in 2012. Likewise, the lake volume increased from 35.8 to 61.6±1.8 million m3 over the past decade. The GPR survey at Imja and Lhotse-Shar glaciers shows that the glacier is over 200 m thick in the center of the glacier. The modeling work at Imja shows that the proposed project will not have major impacts downstream since the area inundated does not reduce considerably unless the lake is lowered by about 20 m. In Huaraz, the results indicate that approximately 40646 people live in the potentially inundated area. Using the flow simulation and the Peru Census 2007, a map of vulnerability was generated indicating that the most vulnerable areas are near the river. Finally, the potential number of fatalities in a worst case GLOF scenario from Lake Palcacocha was calculated to be 19773 with a standard deviation of 1191 if there is no early warning system and 7344 with a standard deviation of 1446 people if an early warning system is installed. Finally, if evacuation measures are improved the number reduces to 2865 with a standard deviation of 462. / text

The transfer of prey resources between ecosystems can have dramatic consequences for both recipient and donor systems by altering food web stability and the likelihood of trophic effects cascading across the ecosystem boundary. Landscape-scale factors influence the importance, direction and magnitude of energy flows, but may also alter the ability of consumer organisms to respond to spatio-temporal changes in allochthonous prey availability. Here, I used flood and drying disturbance gradients to investigate interactions between these two processes on populations of a riparian fishing spider Dolomedes aquaticus (Pisauridae). The abundance of aquatic insects with a winged adult stage, a major component of the diet of D. aquaticus, was markedly higher at less flood-prone rivers and declined with increasing flood disturbance. It was expected that spider populations would be largest at these stable rivers where the aquatic prey abundance was highest. However, a habitat (loose, unembedded riverbank rocks) manipulation revealed that the lack of scouring floods at these sites led to habitat-limited populations, preventing response to the increased prey resource. In fact a peak shaped relationship of spider biomass and abundance was found, with the largest spider populations at intermediately disturbed rivers. In addition, patchy habitat availability was the most likely cause of the small scale (4 m2) aggregation of spiders seen at the most stable and disturbed rivers. These patterns were also associated with strong interactions between the spiders. Stable isotope analysis of field collected spiders and an experimental manipulation of spider densities and food availability indicated that cannibalism rates were likely to be significantly higher at stable and disturbed rivers than those intermediate on the disturbance gradient. Differences in D. aquaticus population size structure and life history traits across the flood disturbance gradient were driven by interactions between resource availability, environmental stability and cannibalism rates. To separate the effects of habitat availability and aquatic prey abundance I used drying rivers, as the amount of aquatic insect prey alters as the water recedes. Desiccation mortality and low aquatic prey biomass most likely caused the spiders' spatial distribution and size class structure to alter in drying river reaches, potentially also leading to differences in cannibalism rates. Overall, cross-ecosystem transfers of prey had large impacts on the distribution, cannibalism rates and life history traits of D. aquaticus but their effects were modified by the nature of the ecosystem boundary. Thus river flow regime controlled the magnitude of the subsidy and its use by a consumer. Hence, cross-ecosystem subsidies will not always lead to larger consumer populations and consumer responses will depend on interactions between large-scale processes.