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150 Peter Allan Wood

150 Peter Allan Wood FIGURE 1. The study basin: Hope River, Jamaica. and is a partly braided, shallow dual-channel floored with poorly sorted material of up to 1 m, and with a slope of 0.013. The river here is incised with the development of terraces, while the active channel has a wide, shallow cross section, and is approximately 32 m wide. Rainfall Most of the catchment receives an average annual rainfall of between 1250 and 2550 mm, most of which falls on a distinctly seasonal basis with a wet season from May to

Ui 100 000 i 10 000- ! 000- 100 1 5 10 20 DISCHARGE m^s Sediment transport in the Hope River, Jamaica 151 /:.-.•• 1 5 10 20 DISCHARGE m 3 /s (A) ALL FLOW CONDITIONS (B) RISING STAGE FIGURE 2. Rating curves for the Hope River. 1 S 10 20 DISCHARGE m 3 /s (C) FALLING S TAGE November. Much of the rainfall is intense, often associated with active cold fronts and slow moving depressions, and rainfalls of about 250 mm a day can occur (Vickers, 1967). Much of this intense rainfall would be transmitted into short lived, high magnitude floods. More detailed accounts of rainfall distribution, intensity and frequency are available (Condie, 1973; Evans, 1972) while Eyre (1968) describes rainfalls associated with Hurricane Flora, 1963. SUSPENDED SEDIMENT Suspended sediment samples were collected for a variety of flow conditions, and when concentrations are plotted against discharge [Fig. 2(A)] it is evident that a great range of concentration exists for the same discharge. However, when sample concentrations collected during rising and falling stages are separated, and then plotted against discharge [Fig. 2(B) and (C)] it can be seen that concentrations are significantly higher for the same discharge during the rising stage than during the falling stage. Hysteresis therefore exists between the suspended sediment concentration and river discharge relationship (Arnborgera/., 1967; Walling and Teed, 1971; Wood, 1977). Suspended sediment at the study section reached concentrations of over 60 000mg/l. Such high concentrations are not common in the literature but have been reported. Perhaps the highest concentrations ever recorded are over 900 000 mg/1. (600 000 ppm) in the Paria River, Arizona (Beverage and Culbertson, 1964). High concentrations have also been reported in the Yellow River, China (Todd and Eliassen, 1938) and in the Rio Puerco, New Mexico (Nordin, 1963). If sampling frequency is sufficient during the passage of a single hydrograph, an individual rating curve can be constructed for that hydrograph (Walling and Teed, 1971 ; Wood, 1977). Such rating curves may exhibit hysteresis resulting in the curve taking the form of a loop with lower values of concentration on the falling limb than

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