Abstract:
This study aims at a monthly rainfall runoff model beginning with WRECU-I Model. It was initiated by Assoc. Prof.Chaipant Rukvichai,Ph.D., Department of Water Resources Engineering, Chulalongkorn University in 1993-1994. The model is nonlinear, lumped and deterministic. The model input are antecedent rainfall during the post 3 month period and the model output is the synthesized runoff for the current month. The study area are the Petchaburi Basin and the West Coast Gulf of Thailand Basin or the Prachuab Kirikhan Coast Basin. The model are used to synthesize runoff of 14 subbasins ranging from 11-7,500 sq.km. in basin area. The model HEC-4PC are adopted to synthesize runoff from rainfall data in a systematic manner for comparison. Finally, the WRECU-I Model are tested with runoff of the Pasak Riverbasin at Station S.9 and the Quae Yar Riverbasin at Station KE.8 which have the basin areas of 14,374 and 4,960 sq.km. respectively. It is concluded that the WRECU-I Model can synthesize monthly runoff very well for Petchaburi Basin and Prachuab Kirikhan Coast Basin. The peak flow synthesized by the model mostly agree with the observed data. Similar results are found with the Pasak Reverbasin and the Quae Yai Riverbasin. However, the low flow resulting from the model are quite different with other models. Consequently, the model use is appropriate with the case of water use study and may be in applicable with the study related to low flow e.g. water quality etc. When compared with the HEC-4PC, the WRECU-I Model can better synthesize runoff during the high flow period in terms of both quantity and time of occurrence. Though, the HEC-4PC give the important statistics of the synthesized runoff very close to those of the observed data. The resulted peak flow are often unreliable comparing with rainfall data.