Showing papers in "Transactions of The Royal Society of South Africa in 1990"
Abstract: SUMMARY Daily sampling of suspended sediment in the flooding Orange River was carried out at Alexander Bay from late February to the end of May 1988. Coupled with simultaneous measurements of water run off, the suspended-sediment data have been used to calculate daily variations in sediment discharge from just before the floods started, through four distinct pulses of varying magnitude and duration, namely the Bloemfontein, Fish River, Kroonstad and Upington floods. During the 3-month period, 24,3 km3 of water, 118,6% more than the mean annual runoff of 11,1 km3, was discharged, varying from 15,5 km3 in March (a record) to 5,3 km3 in April and 3,5 km3 in May. The amount of sediment, transported chiefly in suspension, was substantial but was not in proportion to the amount of water. During March 64,2 × 106t was carried out to sea, the load declining sharply to 9,4 × 106t in April and 7,3 × 106t in May. The total sediment discharge for the three-month period amounted to 80,9 × 106t, which exceeds the mean a...
71 citations
TL;DR: Mortalities were greatest near the mouth of the Orange River, and within 10 km virtually all patellid limpets, mussels, octopus, chitons, urchins, red bait, barnacles and Cape reef worms were eliminated, as were almost all rock lobsters and kelps in shallow waters.
Abstract: SUMMARY Extreme flooding of the Orange River during 1988 led to abnormal dilution of the coastal waters and mass mortalities of intertidal and shallow-water organisms. Species occupying the shallower portions of the subtidal and lower portions of the intertidal zones suffered greatest mortalities. In deeper water mortality was negligible, probably because the fresh water formed a stable layer over the more dense seawater. In the intertidal zone, mortalities tended to be correlated with the physiological tolerances of different species. Mortalities were greatest near the mouth of the river, and within 10 km virtually all patellid limpets, mussels, octopus, chitons, urchins, red bait (Pyura stolonifera), barnacles and Cape reef worms (Gunnarea capensis) were eliminated, as were almost all rock lobsters and kelps in shallow waters. Further south the magnitude of the mortality declined, but even as far south as Brazil (near Kleinzee, ca. 140 km south of the mouth), increased mortalities and other detrimental ...
39 citations
TL;DR: In a follow-up visit in October 1988, it was shown that there will be no long-term negative impact as a result of the floods as discussed by the authors, and birds appeared to have been the most severely affected component of the fauna.
Abstract: SUMMARY During March 1988 a major flood inundated the Orange River mouth. Observations on the impact of the flood on the biota of this region are presented. A total of 315 ha of wetland vegetation was destroyed, either by erosion or by deposition of coarse sediments. Birds appear to have been the most severely affected component of the fauna. Piscivorous birds were unable to locate prey in the turbid water, whereas wading species were deprived of suitable foraging areas. Observations made during a follow-up visit in October 1988 suggest that there will be no long-term negative impact as a result of the floods.
17 citations
TL;DR: In this article, the authors investigated the characteristics of the March 1988 Orange River flood and compared the findings with those for previous floods, showing that the runoff for March 1988 probably has an exceedance value of the order of 1 in 100 to 200 years, although the annual runoff for the 1987/1988 hydrological year is equivalent to only about a 1 in 10 to 15-year event.
Abstract: SUMMARY The March 1988 flood is the best-studied flood that the Orange River has experienced, as far as both its devastating effects and its unusual character are concerned. This paper investigates the characteristics of the flood and compares the findings with those for previous floods. It is shown that the runoff for March 1988 probably has an exceedance value of the order of 1 in 100 to 200 years, although the annual runoff for the 1987/1988 hydrological year is equivalent to only about a 1 in 10 to 15-year event. An account is given of flow characteristics in the mouth of the Orange during the flood, as well as of associated bank erosion rates and scour under the Ernest Oppenheimer bridge.
8 citations
TL;DR: In this article, the authors used both barotropic and baroclinic models to set up the appropriate dynamical framework for the observations of the Orange River's surface signal from both NOAA 9 and LANDSAT satellite imagery.
Abstract: SUMMARY The flow of the Orange River into the Atlantic ocean increased dramatically at the end of February 1988 in response to high rainfall in the catchment areas upstream. This coastal flow is discussed in the light of both barotropic and baroclinic models so as to be able to set up the appropriate dynamical framework for the observations. The surface signal of the warm, fresh river water was deduced from NOAA 9 and LANDSAT satellite imagery, and is shown to form a large anticyclonic eddy (40 km in diameter) at the mouth of the river, and subsequently to flow southwards along the coast in a narrow (15 km wide) plume at 20 ms−1 for some 120 km. An unusual aspect of the satellite observations was the very clear thermal signal seen on 8 and 11 March 1988, which can be ascribed to the fact that very light winds prevailed at this time. Such a flow is to be expected from the theoretical dynamics in the absence of local wind. Later observations showed that after the south-easterly wind increased on 16/17 March...
6 citations
2 citations