Freshwater in adequate supply and quality is vital to life on Earth; however, land-based activities such as development, agriculture, mining and industry, and their associated contaminants, pose a major threat to the quality of freshwater water resources and health of aquatic ecosystems. The upper uMngeni catchment draining into Midmar Dam is a strategically significant water resource, supplying clean drinking water to the eThekwini, uMgungundlovu and Msunduzi municipalities. The quality of this resource is under threat from current land-based activities such as Mpophomeni settlement and agriculture and emerging threats in the form of the Khayalisha social housing project. Monitoring sites were established in varying land use types in three sub-catchments of the upper uMngeni, to assess water quality and ecosystem health impacts of current land uses on Midmar Dam. A suite of physical, chemical and biological water parameters were sampled in conjunction with SASS5 bio-monitoring to assess the associated impacts. Water quality and ecological condition were highest in forested land use and upstream of Mpophomeni where natural land cover and sparse settlement occurred. Marked declines in water quality and ecological condition were observed at areas under commercial agriculture, indicated predominantly by rises in nutrient concentrations and declines in the SASS5 indices. The most notable declines in water quality and ecological condition were observed at sites downstream of Mpophomeni settlement as a result of severe sewage contamination, indicated by high E. coli counts. Nutrient concentrations downstream of Mpophomeni settlement ranged from mesotrophic to hypertrophic, with nitrogen to phosphorus ratios indicative of nitrogen limitation. Ecological condition remained in the ‘seriously/critically modified’ category over the study period. Nutrient loads produced by Mpophomeni are the highest of all the land uses, followed by that of commercial agriculture; both should be viewed as a concern, more so when viewed in terms of their compound effect on Midmar Dam water quality. Current water quality draining the commissioned Khayalisha social housing development area is good and although not natural, is of no contamination concern to Midmar Dam. Results indicate that with current land use activities, urban development and agriculture pose a potential threat to the quality of Midmar Dam resource and that further development in the form of the Khayalisha social housing project may replicate impacts already prevailing in Mpophomeni, whereby a principle water resource may be threatened by eutrophication. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

This study assesses the contribution of agricultural non-point source pollution, to poor water quality of the Vaal River within the Grootdraai dam catchment area. The study evaluates agricultural pollutants affecting the quality of water within the study area. The impact of agricultural non-point source pollution on the water quality of the Vaal River was evaluated by establishing a correlation between the quantity of polluted runoff reaching the River and the quantity of measured nitrates and phosphates in its waters. A questionnaire using random sampling was used to capture data from 15 commercial farmers 35 local residents and the Department of Water Affairs management. The results of the study show that agricultural nutrients are heavily impacting and compromising the water quality of the Grootdraai Dam. The mean concentrations of Nitrogen and Phosphorus were found to be well above the water quality guidelines there by promoting eutrophication. / Environmental Sciences / M. Sc. (Environmental Management)

The suitability of water hyacinth in biogas production was evaluated as a means of waste management in the interests of sustainable energy production. Batch anaerobic digestion (AD) of water hyacinth was conducted to determine the optimal pre-treatment method for maximum methane production. Physical pre-treatment methods produced a highest cumulative methane of 2.3 L during batch AD. The selected pre-treatment method, hand-cutting, was further evaluated in a semi-continuous AD using both mono- and co-digestion. The emphasis was on identifying microbial communities involved and their response to organic loading rates (OLRs). The Illumina Miseq results proved that bacterial communities were more sensitive to disturbances caused by irregular OLRs as compared to archaeal communities. In addition, the variation in substrate nutrients as a result of mono- and co-digestion of water hyacinth, contributed to variations in the bacterial diversity. For example, Bacteroides and Petrimonas diversity varied between mono- and co-digestion. Overall, the study verified that water hyacinth is a suitable feedstock for biogas production and the simple pre-treatment methods are recommended. Furthermore, OLRs influenced the microbial community structure and associated biogas yield. / National Research Foundation (South Africa) / Environmental Science / M. Sc. (Environmental Science)

The most common failure of concrete gravity dams is sliding along the foundation surface. This thesis studies progressive failure of the Longtan dam on the upper Hongshuie river in china.Two methods are used in this thesis; the Safety Reserve Factor (SRF) method and the Overload method. The SRF-method is used as a tool to study sliding failure along the foundation weak layer of the Longtan dam. Strength reduction coefficients decrease the cohesion and friction angle values for the weak layer of the foundation. Simulations with reduced shear strength parameter values gives information about the development of the plastic zone. The ultimate bearing resistance and the failure path along the foundation are obtained. The safety reserve coefficient is established through the strength reduction coefficients, when the plastic zone of the foundation is totally coalescent. To analyse the development of the plastic zone along the dam foundation with the strength reserve method, the commercial finite element software MSC.Marc is used. The results of the Safety Reserve Factor method (SRF) show that the failure of the dam is highly related to the strength of the interface between the dam and rock foundation. The strength reserve factor is determined to 2.4. The Overload method gives a visual deformation shape of the dam structure and pressure load at the moment of failure. / Dammar har används i mer än 5000 år (Yang et al. 1999) och är fortfarande en viktig källa för energiutvinning. Det största antalet dammar finns i Kina och man tror att det finns över 80,000 dammar i landet (Shapiro 2001). En ökning av dammars kapacitet och antal sker, vilket resulterat i ett behov av bättre sätt för att utvärdera säkerhetsparametrar som betongkvalité, styvhet och homogenitet av bergmassa. Simuleringar av dammkonstruktioner kan ge värdefull information om dessa parametrar och kan därigenom bidra till att förbättra en damms stabilitet och sänka konstruktionskostnader. I det här examensarbetet utvärderas och modelleras Longtan dammen i övre Hongshui floden i Kina. Den vanligaste orsaken till haveri av betongdammar är glidning mellan betonglager och bergmassan. I den här rapporten simuleras ett svagare lager mellan betong och bergmassa och utvecklingen av kontaktbrottsvägen visualiseras och utvärderas med progressiva haveri metoden. Det svagare lagrets hållfasthetskoefficienter; friktionsvinkel och kohesion, reduceras för att analysera utbredningen av den plastiska zonen. Resultaten visar att en överskridning av draghållfastheten för betong börjar vid dammens häl och att kompressionsbristningsgränsen överskrids vid dammens tå när hållfasthetskoefficienterna reduceras. Säkerhetsreservskoefficienten för Longtan dammen erhålls då gränsytan mellan betong och berg är helt plastisk. För att analysera utbredningen av den plastiska zonen längs med dammfundamentet med progressiva haveri metoden används den kommersiella finita element mjukvaran MSC.Marc. Resultaten från säkerhetskoefficientfaktormetoden visar att ett haveri av gravitations dammar är i hög grad relaterad till hållfastheten mellan betongen och bergets gränsyta. Säkerhetskoefficientfaktorn bestäms till 2.4. För att bestämma Longtan dammens maximala vattenbelastningskapacitet används Överbelastningsmetoden. Det maximala vattentryck som Longtan dammen klarar av utan att haverera simuleras med hjälp av en vätska vars densitet ökas mellan modellkörningar. Dammens förskjutning når till sist en punkt där den ökar kraftigt och dammens mutationsdeformationstillstånd har uppnåtts. En visuell deformationsbeskrivning av dammen ges genom modellkörningar och överbelastningsfaktorn bestäms.

In general Nile Crocodile Crocodylus niloticus numbers in South Africa appeared to have recovered after persecution and eradication attempts during the last century. Within the last decade, however, the future of South Africa’s Nile Crocodiles seems ominous yet again, as they are faced with renewed threats including habitat destruction and/or degradation. The primary Nile Crocodile populations in South Africa, Kruger National Park, Lake St Lucia and Ndumo Game Reserve are all currently threatened as a result of anthropogenic actions. The vulnerability of South Africa’s major Nile Crocodile populations has highlighted the need for further studies on and assessment of other populations in the country. This study was conducted from April 2009 to July 2010 on the Nile Crocodile population found in Pongolapoort Dam. The aim of the study was to obtain baseline data on the ecology of this previously unstudied population, which included obtaining an estimate of population size and structure, the reproductive dynamics and success of the population, general distribution of the population in the dam and seasonal changes in their distribution. The impact of the impoundment on this population was also discussed. Initial surveys from 1981 and 1989 described few crocodiles in the system. Currently Pongolapoort Dam contains a significant Nile Crocodile population that was previously not considered as substantial. A conservative estimate of 273 Nile Crocodiles was determined for Pongolapoort Dam in 2009-2010. A combination of survey methods allowed for a population structure to be gauged and identified as having 116 juveniles (< 1.2 m), 75 sub-adults (1.2 - 2.5 m), and 82 adults (> 2.5 m). Currently the population has a high percentage of juveniles (42 %), suggesting a growing population, with the proportion of adults (30 %) able to sustain a viable population into the future. From the construction of the Pongolapoort impoundment in 1972 the water level has fluctuated and the surrounding landscape has been altered. As a result the Nile Crocodiles residing in the area had to adapt to the ever changing environment. Their general distribution changed after dam wall completion, when the dam began to fill. First distributional change was a movement out of the gorge section into the newly flooded areas. After the Domoina floods (1983) the dam level rose by over 70 % and the crocodiles moved into the current inlet section. The majority of the crocodile population is now found in the inlet section of the Pongolapoort Dam, utilizing the Phongola River in summer months and residing in the inlet section as historical basking sites during the winter months. Investigating reproductive ecology is essential in order to access the population dynamics of an unstudied population, as reproductive output can be a measure of population health. Reproduction and nesting of Nile Crocodiles in Pongolapoort Dam, and in particular determining the effects of the impoundment on these were investigated. No previous reproductive effort had been documented prior to this study. Crocodiles congregated at a major basking site, where the Phongola River entered the dam, during August 2009 with a 576 % increase in numbers. This signalled the commencement of the breeding season. Females with transmitters made short trips upstream during this time. In November, with the first rains, the river rose and the majority of crocodiles moved up the inlet, and females established nests. Three major nesting areas were identified, two of which were located in the river inlet to the dam. Approximately 30 nesting females were identified during the 2009/2010 nesting season. All nesting areas identified had been used in prior nesting seasons. Nests were located on a variety of substrate types, from clay formed through culluvial and fluvial deposits to course river sand. Several of the nests were predated by Water Monitor (Varanus niloticus). Although the number of nesting females was greater than expected, during the study period there was a total recruitment failure of nests along the river due to a flash flood of the Phongola River in January 2010, destroying all nests prior to hatching. As several juvenile crocodiles were found during surveys, this preliminary study suggests that the Pongolapoort Dam Nile Crocodile population has a relatively high potential reproductive out-put, although their annual successes may vary greatly because of loss of nesting sites because of water level fluctuations and predation. It appears that the impoundment has generally had a positive impact on this Nile Crocodile population recruitment although suitable nesting sites may become limited. There appear to be no current threats to the Nile Crocodile Pongolapoort Dam population, however illegal gill-netting and poaching on the dam and surrounding reserves is on the rise and if not prohibited can result in future problems. A second concern is the high abundance of alien invasive plants that dominate the area, most notably in the river inlet section, the Nile Crocodiles main nesting area. The water quality entering the system is unknown at present and should be tested in future studies to assess whether there may be any reason for concern. In general the Nile Crocodile population in Pongolapoort Dam appears to be one of the least vulnerable and most reproductively successful in South Africa at present. The population has increased dramatically as a result of successful reproductive output even with the ecosystem changes as a result of the impoundment of the Phongola River. It is unlikely that the population increase was as a result of immigration from surrounding areas as the dam wall is a substantial barrier between the dam and the lower crocodile population of Ndumo Game Reserve some 70 km downstream. The high number of crocodiles found through all size classes, juveniles to large adults, also suggests that this population has been stably increasing for a number of years and has a sustainable breeding population. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Submitted in fulfillment of the requirements of the Degree of Master of Technology: Chemistry, Durban University of Technology, 2014. / This project arose out the need for a simple method to analyse NOM on a routine basis. Water samples were obtained from the Vaal dam, which is one of the dams used by a hydroelectric power station. Analysis was preceded by separation of NOM into the humic and non-humic portions. The humic portion was separated into two fractions by employing a non-ionic resin (DAX-8) to separate humic acid from fulvic acid. High performance size exclusion chromatography (HPSEC), equipped with an Ultraviolet( UV) detector and an Evaporative Light Scattering (ELS) detector connected in series, was used to obtain molecular weight distribution information and the concentration levels of the two acids. Mixed standards of polyethylene oxide/glycol were employed to calibrate the selected column. Suwanee River humic acid standard was used as a certified reference material. The molecular weight distributions (MWDs) of the isolated fractions of humic and fulvic acids were determined with ELSD detection as weight-average (Mw), number-average (Mn) and polydispersity (ρ) of individual NOM fractions. The Mw/Mn ratio was found to be less than 1.5 in all the fractions, indicating that they have a low and narrow size fraction. An increase in Mn and Mw values, with increasing wavelength for all three humic substances (HS) examined was observed. The HS, isolated from the dam water, was found to be about the same molecular weight as the International Humic Acid Standard (IIHSS). For the fulvic acid standard, the molecular weight was estimated to be around 7500 Da. Characterization of NOM was done to assist in the identification of the species present in the water. FTIR-ATR was used to as a characterization tool to identify the functional groups in the structure of the humic and fulvic acid respectively present in the Vaal Dam. Analysis of the infrared (IR) spectra indicated that the humic acids of the Vaal dam have phenolic hydroxyl groups, hydroxyl groups, conjugated double bond of aromatic family (C=C), and free carboxyl groups. The isolation method has proved to be applicable and reliable for dam water samples and showed to successfully separate the humic substances from water and further separate the humic substances into its hydrophobic acids, namely, humic and fulvic acids. It can be concluded that the Eskom Vaal dam composes of humic substance which shows that the technique alone gives a very good indication of the characteristics of water. The HPSEC method used, equipped with UV and ELSD was able to identify the molecular weight range of NOM present in source water as it confirmed that the Eskom Vaal dam contains humic substances as humic acid and fulvic acid and these pose a health concern as they can form disinfectant byproducts in the course of water treatment with chemicals. FTIR characterization was successful as important functional groups were clearly assigned. Lastly, the use of the TOC and DOC values to calculate SUVA was also a good tool to indicate the organic content in water. It is recommended to use larger amounts of water must be processed to obtain useful quantities of the humic and fulvic acid fractions.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The design of the Berg River Dam bottom outlet structure with multitude draw offs was based on various hydraulic model tests on a 1:40 model that was used for original design and a 1 in 20 physical model which was used to produce the final design. These tests indicated no foreseeable malfunction and showed that the 1.8 m² air vent would provide sufficient air flow to minimize the negative pressures that would develop behind the emergency gate during its closure or opening. However, during the first trial commissioning of the dam outlet structure, air was unexpectedly expelled through the air vent at a velocity so high that the recta-grids covering the shaft were blown to a height of over 3m while the gate was closing at a rate of approximately 0.0035 m/s. The air flow velocity up the air vent was approximately 45m/s and occurred when the gate was approximately 78% closed. A brief report on the test indicated that the source of air may have been a vortex formation in the vertical intake tower upstream of the emergency gate entraining air which was drawn through the gate and released up the air vent. The purpose of this research was to utilize 3-dimensional numerical modelling employing Computational Fluid Dynamics (CFD) to carry out numerical simulations to investigate the above mentioned malfunction and thereby establishing whether the given hypotheses for the malfunction were valid. For purposes of validating the CFD modelling, a 1:14.066 physical model was constructed at the University of Stellenbosch hydraulics laboratory. The 3-dimensional CFD model was used to investigate the said incident, using steady state simulations that were run for various openings of the emergency gate. The intenetion was to establish whether there was an emergency gate opening which would reproduce the air release phenomenon. The results obtained from the numerical model showed a similar trend to those of the physical model although there were differences in values. Neither model, showed a sudden release of air through the vent. It was concluded that the unsteady air-water flow out of the air vent may have been caused by the variation of the discharge with time causing unbalanced negative pressures in the outlet structure. Therefore, it was recommended that further CFD transient simulations should be undertaken incorporating a moving emergency gate. / AFRIKAANSE OPSOMMING: Die ontwerp van die bodemuitlaat van die Bergrivierdam met multivlakuitlate is gebaseer op verskeie hidrouliese modeltoetse op a 1:40 fisiese model wat vir die oorspronklike ontwerp gebruik is, asook „n 1 tot 20 fisisiese model wat gebruik is om die finale ontwerp te lewer in 2003. Hierdie toetse het geen beduidende afwykings aangedui nie en het bewys dat die 1.8mª lugskag voldoende lugvloei sal toevoer om die negatiewe drukking wat stroomaf van die noodsluis ontstaan gedurende die sluitingsproses, sal minimaliseer. Gedurende die inlywingtoets in die veld in 2008 van die noodsluis, is lug onverwags teen 'n hoë snelheid deur die lugskag opwaarts uitgelaat, wat die rooster wat die skag beskerm teen 'n hoogte van oor 3m geblaas het terwyl die sluis teen 'n tempo van ongeveer 0.0035 m/s toegemaak het. Die lugvloeisnelheid in die lugskag was ongeveer 45m/s en het plaasgevind toe die sluis ongeveer 78% toe was. 'n Kort verslag oor die veldtoets dui aan dat die bron van die lug dalk werwelvorming in die vertikale inlaattoring stroomop van die noodsluis was, met lug wat deur die sluis getrek was en opwaarts in die lugskag vrygelaat is. Die doel van die navorsing was om drie-dimensionele numeriese modellering met rekenaar vloeidinamika (RVD) te benut om numeriese similasies uit te voer om die bogenoemde abnormale werking van die lugskag te ondersoek en daarmee vas te stel of die gegewe aannames van krag is. Vir die doel om die RVD modellering te verifieer is 'n 1:14.066 fisiese model gebou by die Universiteit van Stellenbosch se waterlaboratorium. Die 3-dimensionele RVD model is gebruik om die genoemde probleem te ondersoek, deur stasionêre simulasies wat vir verskillende openinge van die noodsluis geloop is te gebruik. Die doel was om vas te stel of daar 'n spesifieke noodsluisopening is wat die vrylating van die lug veroorsaak het. Die uitslag verkry deur die numeriese model het dieselfde windrigting soos die van die fisiese model gewys, alhoewel daar verskille in die waardes was. Nie een van die modelle het .n skielike vrystelling van lug deur die lugskag gewys nie. 'n Afleiding is gemaak dat die nie stasionêre lug-water vloei uit die lugskag moontlik veroorsaak was deur die verandering van die vloei met tyd veroorsaak deur ongebalanseerde negatiewe druk in die uitlaatstruktuur. Daarom is daar voorgestel dat verdere RVD nie stasionêre simulasies gedoen word met 'n bewegende noodsluis.

[pt] Neste trabalho empregou-se a técnica de redes neurais artificiais e modelos de Box & Jenkins (1970) para análise, modelagem e previsão dos valores de vazão e de cargas de pressão na barragem Corumbá I, do sistema Furnas Centrais Elétricas, a partir dos dados de instrumentação disponíveis desde 1997. A previsão de valores prováveis pode auxiliar em tomadas de decisão durante a operação da barragem. A utilização de métodos estatísticos e de redes neurais artificiais é especialmente recomendado em situações onde a solução através de métodos determinísticos, analíticos ou numéricos, torna-se difícil por envolver modelagens tridimensionais, com condições de contorno complexas e incertezas na variação espacial e temporal das propriedades dos materiais que constituem a barragem e sua fundação. Tradicionalmente, as análises de séries temporais são normalmente abordadas sob a perspectiva de métodos estatísticos, como os modelos de Box & Jenkins. No entanto, redes neurais artificiais têm-se constituído ultimamente em uma alternativa atraente para investigações de séries temporais por sua capacidade de análise de problemas de natureza não-linear e não-estacionários. Neste trabalho são apresentadas três aplicações envolvendo o comportamento da barragem Corumbá I: previsão das vazões através da fundação junto à ombreira esquerda, previsão das cargas de pressão em piezômetros instalados no núcleo central da barragem e no solo residual de fundação e, finalmente, a previsão dos valores das leituras em um piezômetro supostamente danificado em determinado instante de tempo. Em todos estes casos, os resultados obtidos pelos modelos de Box & Jenkins e redes neurais artificiais foram bastante satisfatórios. / [en] In this work, artificial neural networks and the Box & Jenkins models (1970) were used for analysis, modeling and forecasts of water discharges and pressure head development in the Corumbá-I dam, owned by Furnas Centrais Elétricas, from the instrumentation data recorded since 1997. Prediction of the probable values can be a powerful tool for early detection of abnormal conditions during the dam operation. The use of statistical methods and artificial neural network techniques are specially recommend in situations where a solution with a deterministic approach, analytical or numerical, is difficult for involving three- dimensional modeling, complex boundary conditions and uncertainty with respect to the spatial and temporal variation of the material properties of the dam and its foundation. Time series analyses are traditionally carried out using a statistical approach, such as the Box & Jenkins models. However, artificial neural networks have become in the recent years an attractive alternative for time series problems due to their inherent ability to analyze nonlinear and non-stationary phenomena. Three applications of time series analysis, related to the instrumentation data collected from Corumba-I dam, are presented and discussed in this thesis: forecast of water discharges through the foundation near the dam left abutment, prediction of pressure heads in piezometers installed in the impermeable central core and the residual soil foundation and, finally, prediction of the pressure heads that would be read in a piezometer that, at a given instant of time, stops working being supposedly damaged. In all these cases, the results obtained from the Box & Jenkins models as well as the artificial neural networks are quite satisfactory.

A represa das Antas e represa Bortolan fazem parte da Sub-Bacia Hidrográfica do Ribeirão das Antas, sendo que a primeira sofre impacto de uma mineradora de urânio (UTM/INB), uma vez que recebe despejos de efluentes radioativos tratados procedentes de DAM, já a represa Bortolan recebe maior influência da malha urbana de Poços de Caldas. O objetivo do presente estudo foi analisar a diversidade da comunidade zooplanctônica, bem como realizar a caracterização física e química da UTM/INB e represas das Antas e Bortolan. Diferenças em relação às condições físicas, químicas e a comunidade foram verificadas entre os ambientes. Na UTM/INB as condições químicas da água apresentaram-se não favoráveis ao desenvolvimento do zooplâncton. A represa das Antas apresentou condições ambientais intermediárias entre a UTM/INB e represa Bortolan, devido provavelmente ao lançamento de efluentes em condições inadequadas pela UTM/INB. Na represa Bortolan as concentrações de nutrientes e clorofila a explicaram a maior densidade e, portanto, a maior diversidade das espécies zooplanctônicas. / The Antas and Bortolan Dams are part of the Ribeirão das Antas Hydrographical Sub-Basin, being that the Antas Dam suffers impact from a uranium mining (UTM/INB), once it receives discharges of treated radioactive effluents derived from DAM, while Bortolan Dam suffers greater influence from the urban area of Poços de Caldas. The objective of the current study was to analyze the zooplanktonic community\'s diversity, as well as to perform the physical and chemical characterizations of UTM/INB and Antas and Bortolan Dams. Differences related to the physical and chemical conditions and the community were verified among the environments. In UTM/INB, the water\'s chemical conditions were not favorable to zooplankton development. The Antas Dam presented intermediate environmental conditions between UTM/INB and Bortolan Dam, probably due to the release of effluents in inadequate conditions, done by UTM/INB. In Bortolan Dam, the concentrations of nutrients and chlorophyll a have justified the higher density and thus, the greater diversity of zooplanktonic species.

Graduation date: 2006 / Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, sediment accumulated over a dam’s lifetime may be transported downstream; and the timing, fate and consequences of this sediment remain some of the greatest unknowns associated with dam removal. In this thesis, I develop a conceptual model for erosion and deposition following removal of sediment-filled dams in mountain streams, and use field studies to document actual change. The data show that reservoir erosion in mountain rivers is likely to occur by knickpoint migration, with 85% of stored sediment being released during a single storm event in two field studies, at shear stresses less than that required for mobilization of the median surface particle size. Coarse sediment is predicted to deposit close to the dam with channel aggradation decreasing exponentially with increasing distance downstream, although some channel features are shown to have a greater propensity for aggradation than others. Field studies show that turbidity associated with dam removal and reservoir erosion may decrease hyporheic exchange, but gravel deposition (e.g., 470 m3 of gravel from Dinner Creek Dam) has the potential to more than offset that decrease, and increased hyporheic exchange is shown to reduce diurnal temperature change. Macroinvertebrate density and taxa richness did not respond to dam removal itself, but rather with time-lagged reservoir erosion. Following reservoir erosion, macroinvertebrate density recovered quickly, although longterm taxa community composition appears to be altered. On the Sandy River, field measurements of shear stress and patterns of sediment deposition following cold lahars were used as an analog to predict the fate of fine sediment, which is likely to deposit far from the dam. Results show that the Sandy River has little capacity for fine sediment storage in pools above RK 6.4 (~ 42 kilometers below Marmot Dam) at discharges associated with reservoir sediment releases. Taken as a whole, this paper illustrates a complex suite of process that may accompany removal of sediment-filled dams in mountain rivers.