URBANIZATION EFFECTS ON FLOOD RUNOFF AND INUNDATION CHARACTERISTICS IN OGURA BASIN (6)-Proposal of Flood Control Plan Considering Farm Zoning

The Ogura basin located in the south of Kyoto is divided into three drainage sub-basins suchas the Joudan of hill and higher land of 27.4 km2, the Chudan of 6.3 km2, and the Gedan of lowerland of 18.7 km2 contained the reclaimed land of 10.8 km2. The Ogura Pump Station built in 1943at the outlet of the basin has thirteen pumps of 48.9 m3/s in total capacity at present.The basin has been urbanized rapidly in recent years. To cope with changes of flood runoffdue to the urbanization, the improvement of the River Furu being the drainage channel of theJoudan was begun in 1971, and the Kumiyama Pump Station with a pump of 30 m3/s was builtat the downstream end of the River Furu in 1973. These counter-measures, however, are notenough yet to deal with runoff water in the future.In order to make up reasonable flood control plan in the future, we cannot help expecting theeffect of the temporal ponding of runoff water in the reclaimed land. Several proposals describedin previous papers were also based upon this principle under the assumption that almost all part ofthe reclaimed land would be utilized as paddy fields. This assumption, however, may not alwaysbe applicable in the future because of the changes of the socio-economical conditions in recentJapan.In this paper, we propose to classify farm into zones of three classes such as Zone A with thenon-inundation probability of 1/10-year, Zone B of 1/5-year except Zone A, and Zone C with highprobability of inundation which is used only as paddy. A flood control plan is examined to in-crease Zones A and B.The flood control plan proposed in this paper is as follows: 1) For the Joudan: Adding thepumping capacity of 60 m3/s at the Kumiyama Pump Station, and enlarging the side weir in theRiver Furu to 250 m in length being tenfold at present to spill flood flows into the reclaimed land.2) For the Chudan: Reconstructing the side weir at the Main Channel point in the ChudanChannel to spill runoff water into the reclaimed land, and improving the Chudan Channel partly.3) For the Gedan: Adding the pumping capacity of 30 m3/s at the Ogura Pump Station, construct-ing a new drainage channel under the elevated high speed way of the Keiji Bypass Road, andimproving the Main Channel.