Abstract
It is important to investigate thoroughly the change in long-term runoff properties due to land reclamation.Rainfall-outflow records for a period of 12 years, from 1980 to 1991, have been collected for two adjacent catchment areas, namely A and B, at Gojo Yoshino area of the Nara Prefecture.Catchment A is a reclaimed farmland area, while catchment B is a natural forest.The method of ‘paired watershed’ was used to analyze the long-term runoff properties in terms of outflow hydrograph, outflow duration curve, and runoff ratio.
For the summer period characterized by scanty rainfall, the results obtained showed a higher value of total runoff discharge for catchment A.Outflow duration curves for the two catchments showed that the previous finding is valid for outflow depth less than about 0.5mm/d.The difference in runoff ratios for both catchments, during irrigation periods, expressed in terms of water losses was found to be about 112 mm, which was mostly seemed to be attributed to the difference in evapotranspiration.
The results proved that the scanty runoff from the reclaimed farmland is more than that from the adjacent forest; that is, the forest does not play a role in increasing the scanty runoff in this case.
