This system helped to reduce concentrations of nutrients, salts, BOD, COD, SS, heavy metals, and synthetic detergents, before they enter larger watercourses (Matsumoto 1998).
Although with the currently available DCW map it was not possible to assess distances to the nearest minor freshwater source, our results suggest that larger watercourses and water bodies are needed and that small ones alone are unlikely to be sufficient, maybe because they face a higher risk to dry up.
It seems likely that large modern watercourses have remained stable over the past 1 Ma with regards to their trajectory, but with variable water levels.
Currently, a large majority of watercourses in the region are channelized and some are dammed for fish-ponds, but the present-day floodplains had been built earlier by seminatural streams.
This study is important because Bruijnzeel (2004) warned of the lack of studies investigating the effects of vegetation on the flow of watercourses at large temporal and spatial scales.
Irrigation provides the basis for human habitation, whether from traditional systems of underground aqueducts that drain the water-bearing substratum adjacent to runoff watercourses or from large networks of canals.
Environmental concerns relating to the impact of large dams on the upstream watercourse and to the possible effect on aquatic life add to the likelihood that only a few large hydraulic plants will be built in the future.
Most of the pigeons are found below 1000 m (3300 ft), and their prime environment appears to be steep ravine-indented slopes along artificial watercourses, with the occasional large dead laurel tree and much tree heath.
Drainage is mostly intermittent due to the semiarid climate, except for the Parnaíba and São Francisco rivers, with the latter being the major perennial watercourse that intersects a large extent of the Caatinga.
An EA spokesman said: "After several days of heavy rain, the ground is saturated and floodwater from small watercourses continues to flow into larger rivers like the Thames".
