Changes in an urban water resource, an example from Sydney, Australia

Abstract

This paper examines present and future resource utilization in the tidal section of the Georges River in the southern part of Sydney. Over the last 30 years, the physical characteristics of the river have changed as a result of urbanization, changed hydrologic regime and sand dredging. Urbanization has resulted in an increase in population from 190,000 in 1947 to 550,000. This has resulted in an increase in runoff, sediment input to the river and waste disposal. The change in hydrologic regime has resulted in a substantial increase in the magnitude and frequency of flooding which has increased erosion. Sand dredging has increased the channel capacity, enlarged the tidal prism and increased water turbidity. It has also resulted in extensive bank erosion in the upper part of the river and extensive deposition lower down as tailings are deposited. Although most of these changes have resulted in the deterioration of environmental quality, use of the river for recreation and as an urban amenity has increased.

Efectos de las extracciones de áridos sobre el transporte de sedimentos en suspensión en ríos de montaña (alto río Cinca, Pirineo Central)

“…Se han realizado numerosos estudios de los efectos geomorfológicos de las extracciones de áridos (Rinaldi et al, 2005;Rovira et al, 2005), pero son escasos los trabajos que han analizado específicamente el efecto de estas actuaciones en el transporte de sedimentos finos en suspensión (arcilla, limo e incluso arena; Brown et al, 1998). Durante las operaciones de extracción aumenta el material en suspensión debido a la erosión lateral al extraer material del canal (Warner et al, 1977), al paso de maquinaria por el cauce del río (Forshage y Carter, 1973) y a la remoción de materiales y exposición de sedimentos finos al romper la coraza del lecho (Lagasse et al, 1980). Los efectos no son localizados y se pueden extender en el espacio y en el tiempo (kilómetros aguas abajo e incluso aguas arriba, durante años y décadas) hasta que el río alcanza una nueva condición de equilibrio (Kondolf, 1997).…”

River metamorphosis and environmental change in the Macdonald Valley, New South Wales, since 1949

“…Recent studies in central eastern New South Wales have highlighted the importance of a post-1946 secular rainfall change as a cause of river metamorphosis (Pickup, 1976;Young, 1976;Erskine and Bell, 1982;Warner, 1983). The physical impact of this rainfall change, however, may be compounded by recent land use changes, such as urbanisation and sand extraction (Warner et al, 1977). Under these conditions it is difficult, a t best, to isolate the hydrologic and sedimentologic effects of a specific environmental change.…”

Recently increased tropical cyclone activity and inferences concerning coastal erosion and inland hydrological regimes in New Zealand and Eastern Australia

“…Some evidence for increased storminess in eastern Australia was given by Warner et aL (1975). They stated that in the 1930s and for most of the 1940s conditions were much drier in terms of magnitude and frequency of stream runoff events.…”

“…In other situations in parts of eastern Australia and New Zealand there is also evidence that rainfall regirr/es have changed recently and that flood magnitudes have increased (Warner et al, 1975;Healy, 1975;Beable, in prep.). Marked changes are manifest in the mountain lands of the North Island of New Zealand where the present trend is one of accelerated rates of denudation, erosion and sediment transport which in turn are producing numerous downstream practical problems (Cunningham and Stribling, 1978).…”