Weir

About: Weir is a research topic. Over the lifetime, 2765 publications have been published within this topic receiving 22429 citations. The topic is also known as: low head dam.

Flow restoration and protection in Australian rivers

Abstract: Since 1857 new Australians have constructed many thousands of weirs (3600 in the Murray–Darling Basin alone) and floodplain levee banks, 446 large dams (>10 m crest height) and over 50 intra- and inter-basin water transfer schemes to secure water supplies for human use. Flow regulation has changed the hydrology of major rivers on three temporal sales–the flood pulse (days to weeks), flow history (weeks to years) and the long-term statistical pattern of flows, or flow regime (decades or longer). The regulation of river flows is widely acknowledged as a major cause of deteriorating conditions in many Australian river and floodplain ecosystems. In response to mounting environmental concerns, all states, territories and the Commonwealth Government have committed the nation to the principles of ecologically sustainable development and a process of national water reform. Rivers and wetlands are now recognized as legitimate ‘users’ of water, and jurisdictions must provide water allocations to sustain and where necessary restore ecological processes and the biodiversity of water-dependent ecosystems. Progress in the protection and restoration of river and wetland water regimes has been significant, with over half of mainland aquatic systems designated to receive water allocations of some sort. However, exactly how much water they will receive or retain is unclear from the data available. Moreover, the ecological outcomes and benefits of water allocations are not yet apparent in most aquatic ecosystems, with the exception of certain waterbird breeding events, the disruption of algal blooms in weirs and improved fish passage. After reviewing these issues, this paper addresses two vital questions: How much water does a river need? and How can this water be clawed back from other users? Studies conducted to date in Queensland rivers suggest that around 80–92% of natural mean annual flow (and other ecologically relevant hydrological indicators) may be needed to maintain a low risk of environmental degradation. In the Top End of the Northern Territory, some rivers are maintained at 80% of their natural flow, whereas two-thirds of various flow indicators has been proposed as the restoration target for the River Murray, and 28% of natural mean annual flow has been negotiated for the Snowy River in Victoria. To validate these estimates, ecologists are seeking opportunities to turn river restoration projects into long-term hypothesis-driven experiments in ecological restoration, and the funding, time and institutional support to do so. The paper ends with some suggestions to advance the water reforms and achieve higher levels of water allocation for the environment. Copyright © 2003 John Wiley & Sons, Ltd.

Descriptive physical oceanography

Abstract: A translation of "Guide de conception et de gestion des reseaux d'assainissement unitaires", Paris 1996. This text looks at the design and management of combined sewerage networks, covering topics such as: data on rainstorm run-off pollution; different types of weirs and accessories; computation and measurement of characteristics of weirs; evaluation and improvement of hydraulic output and its treatment; location, checking and choice of weir and its improvement; regulations concerning weir wastes; and strategies proposed for action and improvement of knowledge.

Environmental effects of flow regulation on the lower river Murray, Australia

Abstract: Before regulation flows in the lower Murray were highly variable, as for most rivers in semi-arid regions. Major floods promoted large-scale recruitment of flora and fauna in riverine and floodplain communities, and seasonal floods maintained lower levels of recruitment. The regime changed with the construction of 10 low-level weirs in 1922-35, supplemented by the effects of dams in upstream areas. Flows remain variable but are much reduced in volume (about 44%). Low flows (100-300 GI per month) have decreased five-fold and moderate flows (500-1500 GI per month) have increased two-fold. Although the magnitude of peak seasonal flows has been diminished, the timing of flows is unaffected. The effects differ in the Valley and Gorge sections of the river, depending on local development of the floodplain and associated wetlands. The weirs have flooded once-temporary wetlands and contributed to problems of salinization. Weir operations cause daily stage fluctuations that diminish downstream, and the channel is developing a stepped gradient as a consequence of active deposition and erosion. Regulation has limited exchanges between the river and its floodplain, changed the nature of the littoral zone and generally created an environment inimical to many native species, notably fish. The key to rehabilitation may be to restore a more natural balance of low and medium flows, but this may be unrealistic. given the needs of irrigators and other water users. Despite its evolutionary history of wide spatial and temporal variation, the Murray river-floodplain ecosystem evidently cannot accommodate these forms of disturbance.

A review of the ecological effects of river regulation in Australia

Abstract: Responses to hydrologic change are an important theme in lotic ecology, and data for Australian rivers are accumulating in a rapid, butad hoc manner. Thia paper arranges recent contributions according to the major drainage divisions, which provide reasonably coherent environmental units. The east coastal rivers are exploited for storage, power generation and waste disposal, and Tasmanian rivers are regulated to serve hydro-electric power schemes. Most information refers to the Murray-Darling river system, which supplies irrigated agriculture in semi-arid inland areas of S.E. Australia, and is intensively regulated by dams, weirs and barrages. The Murray's flows are over-committed, if variability is taken into account, and there are environmental problems (e.g. erosion and salinity) associated with irrigation. The effects of regulation are seen also in the changed distributions of plants and animals associated with the Murray and its floodplain. In Australia the national effort is uncoordinated because research and management are developing independently of one another. Ecologists must become involved in the planning and implementation of strategies that are consistent, as far as possible, with offstream and instream needs.

Discharge coefficient for sharp-crested side weir in subcritical flow

Abstract: To estimate the outflow over a rectangular sharp-crested side weir, the discharge coefficient in the weir equation needs to be known. Although this type of structure has been designed and used extensively by hydraulic engineers, a universally acceptable discharge coefficient does not exist. In this study over 250 laboratory tests were conducted, and the results were analyzed to find the influence of the flow hydraulics and the geometric, channel, and weir shapes on the coefficient. The results show that for subcritical flow the De-Marchi assumption of constant energy is acceptable, and the weir discharge can therefore be used. Furthermore, it was discovered that the De-Marchi coefficient of discharge is a function of the upstream Froude number and the ratios of weir height to upstream depth and weir length to channel width, whereas the channel slope in subcritical flow can be ignored. Hence, an accurate equation for the coefficient of discharge is introduced.