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flow. Due to the flourishing vegetation growing in the strip, flow velocity decreased
sharply from 28.5 to 10.9 cm/s. In the ponds zone, the flow velocity at the outlet was
very low because of decreased of kinetic energy resulting from a huge water-storage
volume of ponds. The velocity increased between the two ponds for the sloping
stream channel. The riparian buffer zone also presented better capacity of slowing
flow velocity through vegetation and flat relief. The variability of flow velocity under a
discontinuous run-off event was similar to that of a continuous event. But the change
was relative gentle for the intermittent transport of water and relative small run-off
volume. The multiple buffer/detention structure system provided a good opportunity
for sediment and particulate nutrients to settle and transform due to the prolonged
detention time.
Figure 2: The spatial variation of surface flow velocity in the flow pathway
during the continuous and discontinuous run-off event. The dashed
line means run-off transporting in the stream channel between two
buffer/detention structures
Sediment and P-pollutants Concentration Variation in the System
During transporting in the flow pathway, the sediment and P-pollutants concentration
were affected greatly by the multiple buffer/detention structures (Figure 3). In this
research, the typical variation characteristic of pollutants concentration in the flow path
during both continuous and discontinuous run-off events was that the concentration
elevated as input of tributary flow from various agricultural sources (especially village
area) and gradually decreased as run-off passing through each buffer/detention
structure. During a continuous run-off event, the concentrations of TSS, TP, TDP,
DRP in inflow of the whole system were 2.70 g/L, 0.31 mg/L, 0.07 mg/L, 0.05 mg/L,
respectively. But when mixed with tributary flow from the village, the concentrations
of TSS, TP, TDP, DRP were elevated to 3.68 g.L-1, 3.69 mg/L, 0.42 mg/L, 0.38 mg/L,
respectively. After passing through the four stone dams, particulate materials (TSS,
TP) were retained markedly for the formation of better settling conditions by dams.
The proportion of dissolved P-pollutants (TDP, DRP) retained was small. This possibly
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