Tesi sul tema "Catchment loading"

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 89-92).
Despite its tropical climate and abundant rainfall, Singapore is classified as a water scarce country. To protect its limited freshwater resources for both consumption and recreation, Singapore's Public Utilities Board (PUB) has created the Active, Beautiful, and Clean (ABC) campaign. In light of this program, the Massachusetts Institute of Technology (MIT) and Nanyang Technological University (NTU) in Singapore have partnered for various water quality research projects, including sampling of Choa Chu Kang, Bras Basah, Verde, and agricultural areas throughout Kranji Catchment in January 2011. Currently, bacterial levels in Kranji Reservoir are measured by sampling, which is labor intensive and delayed. As an alternative, a model of the surrounding watershed was constructed to estimate bacterial loading to the reservoir as driven by changing weather conditions. The watershed stream network was recreated using ArcSWAT, a version of the Soil and Water Assessment Tool used with geographic information system software. This model is based on a model previously created by Granger (2010). A major improvement is the specification of bacterial loading rates by land use and agriculture type. In order to estimate land-use-specific loading rates, numerous field samples were collected and analyzed for bacterial concentration in January 2011. Nonpoint source bacteria concentrations were estimated from field sample concentrations and applied to the land continuously in the model. Using weather data from January 2005 to February 2007, the model was run twice on a daily time step. The first run included only nonpoint sources, while the second included 23 sewage treatment plant point sources throughout the catchment. Simulated results were compared to independent samples taken in 2009 by Nshimyimana (2010) and indicate a general agreement of order of magnitude, with most measured values within the predicted range. The magnitudes of the nonpoint source run achieved a better fit with field data, although the point source run produced concentration frequency distributions that are approximately lognormal, a characteristic typical of environmental bacteria concentration distributions.
by Ryan Christopher Bossis.
M.Eng.

Pollutants follow various subsurface and surface water pathways from sources within a catchment to its outlet and may cause detrimental effects on downstream water quality and ecosystems. Along their different transport pathways through a catchment, pollutants may be attenuated subject to different physical and biogeochemical processes. In this thesis, physical process effects on such catchment-scale pollutant transport and attenuation, resulting coastal pollutant loading and its efficient abatement are investigated. For this purpose, pollutant transport-attenuation is modeled both generically using a Lagrangian Stochastic Advective-Reactive (LaSAR) approach and site specifically for the Swedish Norrström basin using the GIS-based dynamic nitrogen transport-attenuation model POLFLOW. Furthermore, the role of such modeling for catchment-scale pollutant abatement is also investigated by use of economic optimization modeling. Results indicate that appropriate characterization of catchment-scale solute transport and attenuation processes requires accurate quantification of the specific solute pathways from different sources in a catchment, through the subsurface and surface water systems of the catchment, to the catchment outlet. The various physical processes that act on solute transported along these pathways may be quantified appropriately by use of relevant solute travel time distributions for each water subsystem that the pathways cross through the catchment. Such distributions capture the physical solute travel time variability from source to catchment outlet and its effects on reactive pollutant transport. Results of this thesis show specifically that neglect of such physical solute travel time variability in large-scale models of nitrogen transport and attenuation in catchments may yield misleading model estimates of nitrogen attenuation rates. Results for nitrogen abatement optimization in catchments further indicate that inefficient solutions for coastal nitrogen load reduction may result from simplifying physical transport assumptions made in different catchment-scale nitrogen transport-attenuation models. Modeling of possible future nitrogen management scenarios show also that slow nitrogen transport and reversible mass transfer processes in the subsurface water systems of catchments may greatly delay and temporally redistribute coastal nitrogen load effects of inland nitrogen source abatement over decades or much longer. Achievement of the national Swedish environmental objective to reduce the anthropogenic coastal nitrogen loading by 30% may therefore require up to a 40% reduction of both point sources, for achieving a fast coastal load response, and diffuse sources, for maintaining the coastal load reduction also in the long term.
QC 20100908

The Lake Clearwater catchment, in the Canterbury high country of New Zealand, has a native ecosystem that is adapted to low nutrient conditions. Wetlands in the catchment are identified by the Department of Conservation’s Arawai Kākāriki Wetland Restoration Programme as one of three important endemic wetland types in New Zealand. Uncertainty regarding diffuse nutrient load from agriculture into the lake and wetland ecosystems is limiting effective management of the catchment. This study investigated hydrological processes and nitrogen and phosphorus concentrations to improve knowledge of the sources, characteristics and magnitude of nutrient loading from agricultural land use in this 46 km2 high country catchment. Relevant hydrological data and literature pertaining to the catchment was extensively reviewed. In addition, flow for five key surface waterways was continuously logged at ten sites for 2 years. Concurrently, nutrient concentrations for total nitrogen, nitrate, ammoniacal nitrogen, total phosphorus and dissolved reactive phosphorus were measured at ten surface water sites and three groundwater sites. Total nitrogen and phosphorus load from farmland was calculated from annual flow and median concentrations for four waterways: farmland perennial stream runoff, farmland ephemeral stream runoff, a wetland channel below the farmed hillslope and the lake outlet. Similarly, total nitrogen and phosphorus load for unfarmed land was calculated from the flow and median concentration of two un-impacted perennial streams. Total nitrogen and phosphorus mass balances were calculated and used to estimate subsurface nutrient load and runoff volume from the farmed hillslope. Estimates of subsurface runoff were also made using Darcy’s equation and a water balance. Nutrient load predictions from the Catchment Land Use for Environmental Sustainability (CLUES) model were compared to measured loads. Nutrients were found to be elevated downstream of farmland, especially nitrogen, which was often above relevant guidelines and typical concentrations in upland waterways in Canterbury. Nitrate in farmland subsurface runoff was elevated and was estimated to contribute 52% of total nitrogen yield from farmland. Total nitrogen yield (1.96-2.94 kg ha-1 year-1) for farmed land was comparable to minimum values for pastoral land use in literature but total phosphorus yield (0.093-0.123 kg ha-1 year-1) was well below published values. The range in yield estimates is due to subtraction of a high and a low estimate of natural baseline yield from the measured in-stream yield. Total nitrogen export from the lake (2518 kg year-1) was greater than estimated input (1375 kg year-1) from farmed and non-farmed land indicating an additional source of nitrogen into Lake Clearwater. Total phosphorus export from Lake Clearwater of 58 kg year-1 was 24% less than total estimated loads into the lake (76 kg year-1) from farmed and non-farmed land. Phosphorus was not often above relevant guidelines and the median total nitrogen to total phosphorus ratio in Lake Clearwater (49:1) indicated phosphorus is the limiting nutrient in the lake. Because phosphorus was less elevated relative to nitrogen, an increase in phosphorus inputs could have a greater effect on productivity in the wetland and lake. With corrected land use information, total nitrogen loads predicted by the CLUES model were reasonable but total phosphorus loads were greatly overestimated. Investigation into potential impacts of the elevated nutrient loads described in this study on receiving native ecosystems is recommended to inform conservation efforts.

The most significant human impacts on the hydrological system are due to land-use change. The conversion of land to agricultural, mining, industrial, or residential uses significantly alters the hydrological characteristics of the land surface and modifies pathways and rates of water flow. If this occurs over large or critical areas of a catchment, it can have significant short and long-term impacts, on the quality of water. While there are methods available to quantify the pollutants in surface water, methods of linking non-point source pollution to water quality at catchment scale are lacking. Therefore, the research presented in this thesis investigated modelling techniques to estimate the effect of land-cover type on water quality. The main goal of the study was to contribute towards improving the understanding of how different land-covers in an urbanizing catchment affect surface water quality. The aim of the research presented in this thesis was to explain how the quality of surface runoff varies on different land-cover types and to provide guidelines for minimizing water pollution that may be occurring in the Kuils-Eerste River catchment. The research objectives were
(1) to establish types and spatial distribution of land-cover types within the Kuils-Eerste River catchment, (2) to establish water quality characteristics of surface runoff from specific land-cover types at the experimental plot level, (3) to establish the contribution of each land-cover type to pollutant loads at the catchment scale. Land-cover characteristics and water quality were investigated using GIS and Remote Sensing tools. The application of these tools resulted in the development of a land-cover map with 36 land classifications covering the whole catchment. Land-cover in the catchment is predominantly agricultural with vineyards and grassland covering the northern section of the catchment. Vineyards occupy over 35% of the total area followed by fynbos (indigenous vegetation) (12.5 %), open hard rock area (5.8 %), riparian forest (5.2 %), mountain forest 
 
(5 %), dense scrub (4.4 %), and improved grassland (3.6 %). The residential area covers about 14 %. Roads cover 3.4 % of the total area. Surface runoff is responsible for the transportation of large quantities of pollutants that affect the quality of water in the Kuils-Eerste River catchment. The different land-cover types and the distribution and concentration levels of the pollutants are not uniform. Experimental work was conducted at plot scale to understand whether land-cover types differed in their contributions to the concentration of water quality attributes emerging from them. Four plots each with a length of 10 m to 12 m and 5 m width were set up. Plot I was set up on open grassland, Plot II represented the vineyards, Plot III covered the mountain forests, and Plot IV represented the fynbos land-cover. Soil samples analyzed from the experimental plots fell in the category of sandy soil (Sa) with the top layer of Plot IV (fynbos) having loamy sand (LmSa). The soil particle sizes range between fine sand (59.1 % and 78.9 %) to coarse sand (between 7 % and 22 %). The content of clay and silt was between 0.2 % and 2.4 %. Medium sand was between 10.7 % and 17.6 %. In terms of vertical distribution of the particle sizes, a general decrease with respect to the size of particles was noted from the top layer (15 cm) to the bottom layer (30 cm) for all categories of the particle sizes. There was variation in particle size with depth and location within the experimental plots.Two primary methods of collecting water samples were used
grab sampling and composite sampling. The quality of water as represented by the samples collected during storm events during the rainfall season of 2006 and 2007 was 
used to establish  
water quality characteristics for the different land-cover types. The concentration of total average suspended solids was highest in the following land-cover types, cemeteries (5.06 mg L^-1), arterial roads/main roads (3.94 mg L^-1), low density residential informal squatter camps (3.21 mg L^-1) and medium density residential informal townships (3.21 mg L^-1). Chloride concentrations were high on the following land-cover types, recreation grass/ golf course (2.61 mg L^-1), open area/barren land (1.59 mg L^-1), and improved grassland/vegetation crop (1.57 mg L^-1). The event mean concentration (EMC) values for NO₃-N were high on commercial mercantile (6 mg L^-1) and water channel (5 mg L^-1). The total phosphorus concentration mean values recorded high values on improved grassland/vegetation crop (3.78 mg L^-1), medium density residential informal townships (3mgL^-1) and low density residential informal squatter camps (3 mg L^-1). Surface runoff may also contribute soil particles into rivers during rainfall events, particularly from areas of disturbed soil, for example areas where market gardening is taking place. The study found that different land cover types contributed differently to nonpoint source pollution. A GIS model was used to estimate the diffuse pollution of five pollutants (chloride, phosphorus, TSS, nitrogen and NO₃-N) in response to land cover variation using water quality data. The GIS model linked land cover information to diffuse nutrient signatures in response to surface runoff using the Curve Number method and EMC data were developed. Two models (RINSPE and N-SPECT) were used to estimate nonpoint source pollution using various GIS databases. The outputs from the GIS-based model were compared with recommended water quality standards. It was found that the RINSPE model gave accurate results in cases where NPS pollution dominate the total pollutant inputs over a given land cover type. However, the N-SPECT model simulations were too uncertain in cases where there were large numbers of land cover types with diverse NPS pollution load. All land-cover types with concentration values above the recommended national water quality standard were considered as areas that needed measures to mitigate the adverse effects of nonpoint pollution. The expansion of urban areas and agricultural land has a direct effect on land cover types within the catchment. The land cover changes have adverse effect which has a potential to contribute to pollution.

Lake Ringsjön, located in south of Sweden, has been subject of eutrophication since 1950s and received several restoration efforts. Latest restoration effort, “Project Ringsjön”, was proposed in 2003 to improve lake condition against eutrophication by reducing nutrient concentration. This study was done to assess the nutrient loading into the lake from the catchment of Hörbyån Creek, which is discharging into the lake from southeast. Study addresses the nutrient loading conditions from Hörbyån Creek before and after the implementation of “Project Ringsjön” in 1998 and 2010 respectively. Thus a water quality analysis was performed to observe the changes in total nitrogen and total phosphorus concentration in Hörbyån Creek between these years. Effort was also made to investigate nutrients contribution of different watersheds in the catchment. This study also addresses the effect of seasonal variability and land use on nutrient loading. In order to achieve objectives, annual and monthly water quality modelling was performed on the river. HEC-RAS software was used to simulate water quality variables loading from catchment into the lake, such as nitrates, nitrite, ammonium, organic nitrogen, inorganic phosphorus and orthophosphate. Results indicated increase in average annual total nitrogen concentration from 4.18 mg/l to 4.56 mg/l and reduction in average annual total phosphorus concentration from 0.165 mg/l to 0.083 mg/l in the water discharging into the lake from catchment. The watershed occupying mostly agriculture area was observed to have maximum nutrients contribution, which might be due to high fertilizer leakage. It was also observed that maximum nutrient loading was taking place in November and March; probably due to high runoff generated from precipitation and snow melting that carried additional nutrients to the water bodies. Results also indicated that the studied catchment area was contributing high nutrient concentration for eutrophication in both years; however, there was small decrease in total phosphorus concentration in 2010 compare to 1998.

Glenbrook Lagoon, an 8 hectare lake receiving rainfall runoff from a residential catchment, is experiencing nutrient enrichment problems expressed as excessive aquatic plant presence. This study aims to assess the relative nutrient contribution of the total system compartments, including catchment loading, water column, aquatic plants and surface sediment. This information is utilised in the formulation of management strategies which may produce a sustainable nutrient reduction and general improvement in the system. The total nutrient content of the aquatic system was determined to be high in comparison with the present nutrient loading from the catchment. The ideal management case considers nutrient reduction of the surface sediment compartment firstly, followed by the aquatic plant community, with the water column and catchment influence as relatively low priority compartments. Various strategies for managing these are proposed. The total system benefits of the ideal management case are reductions in nutrients, aquatic plant biovolume and suspended solid loading. Unavoidable constraints placed upon the ideal management case include the excessive aquatic plant presence restricting accessability to the surface sediment for dredging. The resulting best management case requires aquatic plant eradication prior to sediment management, with the total system benefits associated with the ideal management case being retained.
Master of Science (Hons)

Intermittently Closed and Open Lake Lagoons (ICOLLs) are very common along the southern NSW coastline. Expanding urban populations are expanding and these systems are under increasing pressure from anthropogenic activities that change landscape processes and significantly alter the amounts of organic and inorganic constituents entering their waters. Once efficient cycling of nutrients in ICOLLs is overcome, the symptoms of eutrophication establish and the entire ecosystem suffers. These systems have great ecological, social, and economic values that require insightful, well balanced, and educated management to promote sustainable use of these often-sensitive areas. Corunna and Nangudga Lake are ICOLLs in the Eurobodalla Shire on the south coast of NSW. These two ICOLLs receive discharges from catchments covered by native vegetation and grassland. The primary objective of this research component was to quantify catchment exports of total nitrogen (TN), total phosphorus (TP), suspended solids (SS), particulate organic matter (POM) and dissolved organic carbon (DOC) from three small coastal sub catchments that deliver constituents into Corunna and Nangudga Lakes. As part of this investigation the fates of catchment loads in the ICOLLs were established focusing on the lakes water column response to catchment loads and the biogeochemical cycling of nitrogen and phosphorus in sediments.

On the island of Trinidad, intense anthropogenic activity and inappropriate land use on terrain vulnerable to erosion and rapid runoff lead to severe sedimentation in the watercourses. A major impact is an increase in flood risk during the strong storm events characteristic of the tropical rainy season due to reduced channel capacity. This study addresses the problem of sedimentation in the Acono River in light of the high sediment loadings observed at the outlet of a 6.6 km2 steep catchment where an operating limestone quarry is located. A hydrologic and sediment measurement network was developed to estimate the impact of the quarry on the sediment loadings in the Acono River for several storm events during a year. Results indicated that the quarry yields tremendously more sediment than the rest of catchment. The MUSLE model was used to estimate sediment yield from soil erosion for individual rainfall events and provided good results. Several sediment transport formulae were used to determine both suspended and bed load sediment discharge during rainfall events. The significant deviation of the computed values from the measured values showed how difficult it is to predict sediment discharge in natural rivers, particularly where washload is a significant component.
Sur l'île de Trinité, une activité anthropique intense, couplée à une utilisation inadéquate de sols propices à l'érosion et à un ruissellement de surface rapide, implique une forte sédimentation dans les cours d'eau. Une conséquence est l'augmentation du risque d'inondation durant les intenses précipitations de la saison humide, en raison d'une réduction de la capacité d'écoulement de ces cours d'eau. Ce projet étudie les problèmes de sédimentation dans la rivière Acono, à la vue des importantes quantités de sédiments à l'exutoire d'un bassin versant de 6.6 km2 où une carrière de calcaire est exploitée. Un réseau de mesure hydrologique et sédimentaire a été développé afin de mesurer l'impact de cette carrière sur la charge sédimentaire dans la rivière Acono au cours de plusieurs événements pluvieux. Les résultats indiquent que la majorité des sédiments transportés provient de la carrière en comparaison du reste du bassin versant. Le modèle MUSLE a fourni une estimation satisfaisante des quantités de sédiments transportés au cours des événements pluvieux analysés. Plusieurs équations ont été utilisées pour déterminer la charge sédimentaire en suspension et par charriage durant ces événements. La différence entre les prédictions et les mesures effectuées sur le terrain illustrent la difficulté de prédire la charge sédimentaire dans des cours d'eau naturels.

碩士
國立成功大學
環境工程學系
106
Eutrophication is a common water quality problem of reservoirs in south Taiwan, and most of reservoirs which was identified as the eutrophic reservoir because of low transparency instead of chlorophyll-a. The cause of low transparency are mainly high concentration of suspended solids instead of chlorophyll-a. The strategy of restoring eutrophic reservoirs must be based on science as integrating watershed and bio-optical models for liking catchment loading to the depth of Secchi disk to simulate different load reduction scenarios. Therefore, this study was integrating watershed model, receiving water model and Secchi disk depth physical model to develop an integrating model. The result of HSPF watershed hydrological modeling is acceptable. The simulated total inflow rate is close to observed inflow rate. The R2 value of calibration and validation are 0.5929 and 0.7574 respectively. According to loading estimation result, the loading constituents includes SS, NH4-N, NO3-N, NO2-N, TP, TOC, and BOD¬. The sources of pollutant loading in Agongdian Reservoir are point source from residents, nonpoint source, and cross-watershed diversion. Nonpoint source and cross-watershed diversion are the main resources with more than 95% proportion, and point source with less than 5% proportion. The variation trend of total loading is similar to precipitation change. There are three loading reduction scenarios are simulated in this study. (1) Point source control: SS is reduced from 200mg/L to 20mg/L. TOC is reduced from 3.93 to 0.8 mg/L. PO43- is reduced from 1.33 mg/L to 0.16 mg/L. BOD is reduced from 5.92 to 2 mg/L (2) Nonpoint source control: TP and TN emission are reduced to 70% in fruit land. (3) Cross-watershed diversion control: SS is reduced to 60% and TP is reduced to 80%. In the result, the cross–watershed diversion control is the most effective one. Agongdian Reservoir is identified as eutrophic due to overloading of SS loading which leads to low transparency.

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.

Glenbrook Lagoon, an 8 hectare lake receiving rainfall runoff from a residential catchment, is experiencing nutrient enrichment problems expressed as excessive aquatic plant presence. This study aims to assess the relative nutrient contribution of the total system compartments, including catchment loading, water column, aquatic plants and surface sediment. This information is utilised in the formulation of management strategies which may produce a sustainable nutrient reduction and general improvement in the system. The total nutrient content of the aquatic system was determined to be high in comparison with the present nutrient loading from the catchment. The ideal management case considers nutrient reduction of the surface sediment compartment firstly, followed by the aquatic plant community, with the water column and catchment influence as relatively low priority compartments. Various strategies for managing these are proposed. The total system benefits of the ideal management case are reductions in nutrients, aquatic plant biovolume and suspended solid loading. Unavoidable constraints placed upon the ideal management case include the excessive aquatic plant presence restricting accessability to the surface sediment for dredging. The resulting best management case requires aquatic plant eradication prior to sediment management, with the total system benefits associated with the ideal management case being retained.