• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2757
  • 1245
  • 495
  • 220
  • 199
  • 133
  • 133
  • 133
  • 133
  • 133
  • 126
  • 58
  • 56
  • 51
  • 46
  • Tagged with
  • 6576
  • 1317
  • 894
  • 828
  • 615
  • 605
  • 551
  • 507
  • 460
  • 434
  • 390
  • 349
  • 334
  • 311
  • 311
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Conjunctive management of groundwater and surface water resources in the Upper Ovens River Valley

Lovell, Daniel Martin January 2009 (has links)
The Upper Ovens River catchment is located in the Victorian high plains of Australia. With an absence of major storages or weirs, the flow regime of the Upper Ovens River is close to its natural magnitude and frequency. Water extraction from rivers has the potential to negatively impact on environmental flow requirements and management of extraction is required to maintain flows to the river, especially over the low flow summer periods. The Upper Ovens River has been shown to have a high connectivity between groundwater and surface water, and for effective protection of stream flow, it is proposed that groundwater and surface water are managed conjunctively by a government legislated Water Management Plan. Environmental stream flow objectives have been identified, but no method exists to link these to groundwater objectives. Without this link, water resource managers cannot develop management methods or plans for management of groundwater to achieve surface flow objectives. / Existing data commonly available to water resource managers was analysed to develop a method to link stream flow objectives to groundwater management objectives, and investigate the groundwater-surface water relationship and water cycle in the Upper Ovens catchment. A water balance for a well defined sub-catchment was developed for the period between 1975 and 2005 to investigate the water cycle and magnitude of fluxes between groundwater in the unconsolidated sediments of the valleys and surface water. Darcy’s law and statistical regression analysis of commonly available historic data were used to develop the understanding of the groundwater-river level relationship and produce a method for relating environmental river flow targets to groundwater levels. A set of conjunctive management principles for resource managers was produced based upon the sound scientific understanding of groundwater-surface water interactions. / The mean water balance shows a clear seasonal pattern for movement of water between surface water and groundwater. Groundwater levels have remained steady, with average annual groundwater recharge from rainfall and the river of 9,773 ML nearly equal to average annual discharge of 9,584 ML from the aquifer as baseflow or evaporation in the dry season. Generally extraction of groundwater and surface water (3,200 ML/yr) and fluxes between groundwater and the river (2,626 ML/yr), are only minor components of the water balance (560,000 ML/yr) and do not affect the flow patterns in the Ovens River. However, in years with very low flows over the Summer/Autumn period, extraction from the river can significantly reduce flow in the river. Management of river flow at this time is the focus for water resource managers. / Field measurements and regression relationships showed a rapid rate of flux between groundwater and the river with the time lag (for rises in river level to subsequent rises in groundwater levels) increasing with distance of the aquifer from the river to be 14-20 days at the maximum measured distance of 750 metres from the river. With the narrow width of the unconsolidated sediment aquifer (less than 3000 metres) extraction of groundwater from these aquifers is expected to impact on stream flows within the summer period (90 days). / Regression analysis produced equations for relating Ovens River levels to groundwater levels with a high correlation. These equations can relate stream flow objectives to corresponding groundwater management that can be used by resource managers with a high level of confidence. Groundwater and surface water, in the form of river flows, are intrinsically linked and to protect flows in the Ovens River during times of low flow, groundwater has to be managed in line with surface water. Four principles have been identified for conjunctive management in the Upper Ovens, and resource managers should set management rules based on the following principles: 1) Groundwater and surface water are hydraulically connected, manage as one; 2) Restrict groundwater extraction in line with surface water restrictions; 3) Manage groundwater to minimum groundwater levels; and 4)Manage groundwater in the unconsolidated sediments as one aquifer.
232

Patterns of River Breakup Timing and Sequencing, Hay River, NWT

Kovachis, Nadia 06 1900 (has links)
River ice breakup and associated flooding are realities for many northern communities. This is certainly the case in Hay River, NWT, which is located at the junction of the Hay River and Great Slave Lake. Hay River experiences a wide range of spring river ice scenarios; from docile thermal melt outs, to severe ice jams resulting in life-threatening, disastrous flooding. This study involved the analysis of five seasons of aerial and time-lapse photographs, water level measurements and hydrometeorologic data. This work also compiled an extended historical record of breakup in the Hay River delta, which was compared against the field data gathered for this study; combining local, experiential knowledge with scientific observation into a cohesive description of breakup. This will be used to advise the non-technical flood watch community on the patterns of timing and sequencing of breakup, which is critical for evacuation planning. / Water Resources Engineering
233

Navigating imperialism in China steamship, semicolony, and nation, 1860-1937 /

Reinhardt, Anne, January 2002 (has links) (PDF)
Thesis (Ph.D.)--Princeton University, 2002. / Adviser: Susan Naquin. Includes bibliographical references.
234

Cretaceous tectonic history along the Salmon River suture zone near Orofino, Idaho : Metamorphic structural and ⁴⁰Ar/³⁹Ar thermochronologic constraints

Davidson, Gary F. 30 May 1990 (has links)
Graduation date: 1991
235

Landslide occurrence in the Elk and Sixes River basins, southwest Oregon

McHugh, Margaret H. 10 December 1986 (has links)
Timber management of coastal watersheds in southwest Oregon has been complicated by the need to protect anadromous fish habitat from accelerated stream sedimentation resulting from management activity. The rugged terrain of the Elk and Sixes River basins is underlain by the complex geological province of the Klamath Mountains, in which landslides are a common, natural, and important process of sediment production. A landslide investigation, using sequential aerial photographs which covered a time period of 37 years, was used to determine relationships between mass-wasting, geologic types, and timber harvest practices. Averaged over all rock types, harvested areas showed an increase in failure rate of 7 times, and roaded areas an increase of 48 times that of forested terrain. Terrane underlain by dioritic intrusions was the most sensitive to road-related activity, with an increase in failure rate of up to 108 times that of comparable unmanaged land. The complexity of lithologies and deformational history in the area strongly influence slope morphology, and produces characteristic soil types which experience predictable modes and rates of slope failure. Debris slides and torrents are the dominant form of mass-wasting in dioritic and Cretaceous sedimentary terrane. Areas underlain by more clay-rich metamorphic bedrock are prone to slumps and planar streambank failures. Stream morphology is profoundly influenced by both rock type and geologic structure. Within an area characterized by steep, deeply incised streams, several persistent low-gradient reaches were delineated. These low-gradient stream reaches occur where (1) large landslides have locally raised channel bed elevation and (2) valley-floor widening has occurred in sheared rocks along fault zones or in more readily eroded rock types upstream of rock types resistant to fluvial erosion. / Graduation date: 1987
236

Requirements for successful irrigation systems in the Senegal River Basin (Mauritania)

Abba, Fatima Zahra 19 December 1995 (has links)
Implementation of a small-scale irrigation project in southern Mauritania is analyzed in this report. The main objective is to demonstrate that small-scale irrigation farming is the best suited solution for Mauritania's agriculture. To reach this objective different steps are taken in this study. The first step highlights the different aspects affecting the development of agriculture in the Senegal River basin such as climatic, environmental, and socio-economic constraints. The next step is the design of a small-scale irrigation system for a small region in the middle valley of the Senegal River called the Dirol plain. Finally, analysis and discussion of the design is made. This discussion centers on the problems faced during the design and the different assumptions made to implement it. The conclusion section addresses the feasibility of the design and gives recommendations that will help improve the design process for future work in the Senegal River basin. / Graduation date: 1996
237

A Riparian Portal

Csonti, Miklos January 2012 (has links)
Modernization and its conveniences have obscured our relationship with the natural environment. We no longer have to personally interact with nature when consuming its resources. Consequently, we lack direct feedback from our exploits, and have lost any moral sensibility towards the finite resources of our planet. This unwanted consequence of modernity has perhaps most explicitly manifested itself on the urban riverbanks of the developed world. Such riparian landscapes, once animated with human activity, have become desolate environments, often programmed solely to serve utilitarian functions. At best, some have been revitalized to accommodate recreational amenities, but the direct interaction that was once necessary to utilize the river for its resources has been replaced by invisible machinery, turning the river’s role in sustaining the city into an abstract concept. The condition found on the banks of the Danube River in Budapest is the epitome of this unfortunate phenomenon. While inhabitants draw water from the faucet, buy fish in the supermarket, and expel waste into an enigmatic drain, the riverbank is far out of sight, deserted, and the river’s role in satisfying their needs is never considered. Instead, the Danube is revered only for the pomp and grandeur it bestows upon the extravagant portrait of the boastful city. In response to this skewed perception, this thesis presents a proposal on the site of Széchenyi Square, located at the base of the Chain Bridge in the heart of Budapest. Historically significant as the main port and gateway to the merchant town of Pest, the Square has since abandoned its role as mediator between city and river, and has instead become a mediator of automotive traffic. The proposal presented in this thesis revives its role as a gateway, but not in the traditional sense. It conceives a riparian portal that allows the passer-by to experience an alternate reality – a place where nature and city are superimposed, and the modern individual is granted direct interaction with his natural resources.
238

Distribution of Organotin Compounds in Love River and Chen-Chang River of Kaohsiung

Li, Li-Ting 17 August 2011 (has links)
Kaohsiung Harbor is the largest international sea port in Taiwan, a lot of ships around the world pass in and out frequently, the pollution of organotin is very serious in the harbor area. Love River and Chien-Chen River may be polluted by the seawater tidal action from the Kaohsiung harbor. Domestic, industrial and agricultural wastewaters discharged into the upstream sections may also cause the pollution of organotin. The purposes of this study were to understand sources of organotin pollution by analying the content of organotin compounds and to monitor the organotin pollution of the rivers in Kaohsiung. Samples including surface sediments and riverwaters were collected from nineteen stations of Love River and Chien-Chen River. The results revealed that concentrations of MBT, DBT and TBT in the riverwaters of Love River varied between 13.4-43.6, 2.6-9.9 and ND-13.5 ng/L as tin. The concentrations of MBT, DBT and TBT in the riverwaters of Chien-Chen River were 3.1-28.1, 2.1-10.9 and ND-9.1 ng/L as tin, respectively. The concentrations of MBT, DBT and TBT in the surface sediments of Love River varied between 20.6-92.3, 7.6-26.2 and ND-15.4 ng/g as tin. The concentrations of MBT, DBT and TBT in the surface sediments of Chien-Chen River were in the range of 22.4-70.0, 6.4-14.1, ND-31.9 ng/g as tin, respectively. MBT and DBT were detected in all the samples of all the sampling stations of Love River and Chien-Chen River. Distribution of organotin compounds in riverwaters and surface sediments showed a consistency between these two rivers. No phenyltin pollution was detected at all stations, probably due to the decline in agricultural activities and the ban on utilizing triphenyltin acetate as pesticide. Except the highest organotin pollution appeared in the outfall of Love River and Chien-Chen River, other high values of pollution were found near the upper reaches of both rivers.
239

The distribution of the Polycyclic Aromatic Hydrocarbons in the Love River and Chianjen River

Lee, Yu-hui 10 August 2005 (has links)
Turning back to look Kaohsiung city¡¦s development and history of exploitation, both of them had a close relationship with the Love River and Chianjen River. Along the rivers, there are numerous industrial estates and large population. The basin of the rivers is important in politics and economy to Kaohsiung. However, the development of Kaohsiung also causes organic pollution, such as polycyclic aromatic hydrocarbon (PAHs), released to water system. Furthermore, some of these pollutants are carcinogenic, so that this topic is quite important. This study investigates PAHs concentrations and seasonal variations in sediments and suspended solids of these two rivers. Total PAHs concentrations varied from 110 to 4300(ng g-1 dry wt) in sediments and 1500 to 7000(ng g-1 dry wt) in suspended solids of the Love River. Total PAHs concentrations of sediments and suspended solids of the Chianjen River exhibited in the range of 230-3900 (ng g-1 dry wt) and 490-9200 (ng g-1 dry wt), respectively. The average PAHs concentration during rain/ dry season of the Chianjen River is significantly higher than those of the Love River. Compared with global data in literature, level of total PAHs concentrations in sediments and suspended solids of the Love River and Chianjen River belongs to moderate pollution. Total PAHs and total organic carbon (TOC) is significantly related except suspended solids of the Chianjen River. However, the relationship between total PAHs concentrations and mean particle size is not significant because of inequilibrium resulted from different sources. Referring to Sediment quality guidelines (SQGs), most of stations are in safe range, only total PAHs concentrations at station L8 in rainy season is significantly higher than the standard ERL value. For each individual compound, the concentrations of many low-molecular-weight PAHs are higher than their standard ERL¡BLET and LAET values. The result of HCA shows that in both dry and rain season, these two rivers¡¦ sediments and suspended solids are separated into upstream and downstream groups. It is believed that the existence of an intercept device set up in midstream of both rivers is the reason. The PAHs in sediments of the Love River is mainly contributed from automobile exhaustion, while suspended solids in the Love River is mainly contributed from petrogenic source. However, both sediments and suspended solids in the Chianjen River are mainly contributed from combustion pollution.
240

A forest of disputes struggles over spaces, resources, and social identities in Amazonia /

Ioris, Edviges Marta. January 2005 (has links)
Thesis (Ph. D.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 326 pages. Includes vita. Includes bibliographical references.

Page generated in 0.0358 seconds