No description available.

No description available.

Not available. / Thesis (M.T.R.P.)-University of Natal, 2003.

No description available.

The wandering river pattern represents one of the last remaining river patterns that are not well understood. Many aspects of these rivers are not well known, particularly the processes of their creation and maintenance. The term wandering describes gravel or cobble bedded rivers, transitional between braided and meandering, with multiple channel sections around semi-permanent islands connected by single channel sections. This dissertation investigates the controls on the characteristics of wandering rivers within the Miramichi region of New Brunswick through time and at three nested spatial scales. / At the scale of rivers, three factors appear to be needed for wandering to occur: (1) wide valleys, (2) channel energy between braiding and meandering, and (3) avulsion triggers, frequent overbank flows caused by icejams in the Miramichi. Principal component analysis showed that larger wandering rivers displayed greater anabranching intensity than smaller rivers, perhaps related to higher stage ice jams within larger rivers. / At the scale of channels, the wandering pattern of the Renous River was found to be in a state of dynamic equilibrium, with channel creation balanced by channel abandonment. The anabranch cycle model was developed to illustrate the temporal dynamics of anabranch creation, maintenance and abandonment within wandering rivers. / Also at the channel scale, principal component analysis of channel reaches within the Renous River displayed differences in grain size and hydraulic efficiency between side-channels and main-channels. Energy and sediment mobility within side-channels was related to their formation, maintenance and abandonment. Energy and sediment mobility within main-channels was related to mega bedforms called bedwaves. The apex of some bedwaves occurred at diffluences. / At the scale of channel elements, diffluences are stable where a large bar is formed and accretes upstream, creating a large reservoir of sediment upstream of anabranch channels to buffer their degradation. Where diffluences are unstable, a large bar forms within one anabranch channel to partially block flow and may cause its abandonment. The dissertation illustrates that within wandering rivers, processes occurring at multiple spatial and temporal scales interact to create and maintain the pattern.

Growth of riparian cottonwoods along regulated rivers can be limited by water availability. In this study we associate seasonal variation of environmental conditions and stream flows with water relations of a natural cottonwood grove located along a regulated river in southern Alberta. To link elements in the river-soil-plant-atmosphere continuum, river and groundwater levels and precipitation were monitored; sap flow was continuously measured with thermal dissipation probes in eight trees and stomatal conductance and leaf water potential were measured monthly; and weather conditions were monitored. From June through August, stomatal conductances at both leaf and canopy levels were increasingly limited by decreasing water availability. Artificially increasing the soil moisture in August resulted in an increase in sap flow and stomatal conductance at leaf and canopy levels. These responses can be attributed to seasonal changes in the water potential difference between soil and leaves or an alteration in hydraulic conductance, or a combination of both. / xiv, 135 leaves : ill. ; 29 cm

No description available.

This thesis relates fluvial morphology to those hydraulic conditions identified as being ideal for the rearing of juvenile Atlantic salmon. The suitability of flow depths and velocities were obtained from published habitat preference curves in order to compute the percent area (percent usable area - PUA) and average width (average usable width - AUW) of reaches providing ideal rearing habitat for juvenile Atlantic salmon at 2 typical summer discharge levels, in the Ste. Marguerite River. / By dividing reaches into smaller, morphologic unit's, in order to make the conditions more uniform, it was noticed that the wetted width and the amplitude of the vertical oscillation of riffles and pools (riffle-pool amplitude) provided the strongest hydraulic and morphologic relationships with the amount of usable habitat at the morphologic unit scale. Two regression models were produced to estimate the AUW of morphologic as a function of hydraulics and morphology, respectively. / The historic flood in July 1996 also provided an opportunity to examine some of the impacts of a large magnitude flood on channel morphology: localized bed and bank erosion, the destruction of riparian vegetation, the enhancement and destruction of individual bars, and localized changes in the hydraulic and morphologic character (induced by large sediment inputs).

Subsequent to the impounding of the Pongolo river in the 1970's, development of irrigated agriculture on the Makatini flats has been reducing the area of vegetation available for grazing, and flooding patterns on the seasonally inundated Pongolo River Floodplain have been determined by the controlled release of water from the Pongolapoort dam. About 50 000 people live along the 10 000 ha floodplain within the 63 000 ha northern region of the flats which was studied. This population includes 2 970 registered cattle owners who own a total of 19 300 cattle. The objectives of this study were: to gain an understanding of the Makatini pastoral system which would facilitate prediction of the effects of potential developments, including agricultural expansion, modification of floodplain hydrology and changed cattle management practices on the utility value of cattle; and to provide guidelines for the management of pastoral resources on the Makatini and other traditional African pastoral systems. It was established that the value of cattle cannot be determined without understanding the importance of the subsistence utilities provided and that the value of utilities relative to each other influences the way in which the system is stocked and managed by the local people. The value of all marketed and non-marketed utilities was determined and the implications of the economic evaluation for the identification of management options in African pastoral systems assessed. Despite the "low productivity" of the Makatini system compared to western style ranches, cattle owners receive annual returns worth approximately 100 % of the asset value of their stock. This explains low market offtake rate in this and other subsistence systems. Non-marketed utilities, particularly milk production provide most of the returns to cattle owners. The mean stocking density on the floodplain vegetation was estimated to be three times that of dry-land areas, but only 23 % of all grazing time is spent on the floodplain. Although floodplain forage provides an important supplement to winter grazing, its use is not vital to maintenance of animal condition. The coincident occurrence of an annual "stress period"; greater acceptability of Echinochloa pyramidalis vegetation as forage; the absence of floods; and the reduced use of floodplain fields, results in increased floodplain use in winter to a stocking density approximately ten times that of dry-land areas. How the floodplain hydrology, rainfall and grazing interact with the crop growth rate and quality of E. pyramidalis stands was examined. The forage production potential of E. pyramidalis was found to be higher than that of other floodplain vegetation types and stocking densities of up to 4.5 AU/ha in summer and 2.5 AU/ha in winter are considered possible on the Pongolo floodplain. Echinochloa pastures may become wet and cause scouring if grazed exclusively, but grazing reduces plant moisture content and makes the forage more acceptable. Local pastoral management was found to depend on the collective activities of cattle owners in pursuit of personal needs in a dynamic socio-economic context. Motivation for the manipulation of cattle numbers and herd composition is dictated by a cattle owner's perception of his needs for utilities and his ability to access those benefits. Because of this, the pastoral practices were found to be closely linked to other socio-economic activities such as agriculture and migrant labour. stock owners have a narrow perspective of pastoral resource management and use strategies developed on small spatial and temporal scales. In contrast development planners tend to identify objectives on a regional scale and on long-term (10 - 50 year) time scales and to orient management towards maximising the value of marketable utilities and preventing long-term overstocking. Management of pastoral resources in traditional African systems requires that the needs of local people be met, that the resource base be maintained; that pastoral policy be developed as a component of regional development planning and that close liaison between interest groups be maintained. Failure to establish or maintain this liaison is considered the main reason for the failure of many African pastoral development programmes. It was recommended that local pasture management committees be established on the Makatini and that extension officers, trained specifically to understand management problems of Third World pastoral systems, be used to maintain liaison between stock owners and development planners. It was also suggested that formal cattle camps be established and managed by local people and that at least one flood (river flow> 200 cumecs) be released from the Pongolapoort darn each summer. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1988.

This thesis explores the changing environment of the middle and lower Yellow River basin from the Zhou to the reign of Han Emperor Wu (ca. 1045-87 B.C.), a period characterised by an increase of government control over the land along with an intensification and expansion of agriculture. The second chapter employs palaeoecological sources to look at the early environment of the region, arguing that the eastern plains were mixed forest-steppe, and that the regions to the west were mostly steppe. The third chapter uses archaeological sources to explore the rise of civilisation, the fauna of the region in the Shang period and the spread of iron tools. The fourth chapter is divided into two sections, the first of which looks at what can be learned from the texts of the period concerning agriculture, land clearance, deforestation, hunting, fishing and economic geography. The second half concerns the intensification of state power in regulating and transforming natural environments through legal measures and water control projects, as well as the development of a market economy.