However, it also includes a series of small reservoirs, which influence both peak runoff and percentage runoff (Kilmartin, 1994). In sum, for the most part, the catchment acts according to theoretical predictions and responds directly to rainfall. Subsequent peak flow is then enhanced by an increase in the effective size of the catchment area (Figure 2). However, since the spoil surface is not regular, the depressions where marshy areas develop and ponding occurs act as reservoirs that remove some of the catchment from active participation until they overflow, often engaging soil pipe systems in the process. Because interflow is rapid, this means that response times and also flow durations are short. Since the amount of soil storage is small, and sites where ponding may occur are relatively few, most of the catchment contributes to stream flowing and the rising limb of the hydrograph is very steep. When runoff-inducing rainfalls occur, the first runoff is surface and near surface interflow through the artificial soil, which travels to the channel directly. Storage here is controlled by recent rainfall history and by evapotranspiration. Finally, there is storage in natural and artificial ponding areas, some due to subsidence and irregularities in the largely impermeable mine-spoils that underlie the highly permeable artificial topsoil layer applied during land reclamation. Second, there is storage in the channel, which is mainly related to the immediate rainfall. the three modes of on-site storage, first, there is a small amount of water storage in the thin active layer of the topsoil, which is directly related to rainfall in the days immediately prior to the event.
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