Tsuyoshi Tada

MODELING OF FLOOD FLOW FRONT ON STRIP ROUGHNESS

The speed of flood front under dry-bed condition with strip roughness is measured and investigated with experiment and numerical simulation. The influences of the roughness spacing and its height and on the flow conditions are especially investigated. It is shown that the factors affecting the speed are backwater effect by the head strip and flow restraint effect by other strips. One dimensional numerical model for flood flows simulation on strip roughness is developed. The model employs both effects and improves accuracy of shallow flow on large roughness.

FUNDAMENTAL STUDY ON SPATIAL RESOLUTION OF TOPOGRAPHIC INFORMATION FOR RUNOFF ANALYSIS

Spatial resolution of topographic information gives a great influence to distributed runoff analysis. The objective of this study is to evaluate the effects of spatial resolution of DEM (Digital Elevation Model) on flood analysis with 1-D main flow channel. Kinematic wave propagation is simulated through real and imaginary river channel data sets having various resolutions. This study reveals that (1) Low resolution of DEM shortens delayed time of peak discharge, because smallhorizontal curves of river channel are omitted and channel elements become shorter;(2) Vertical curves in channel profile have also significant influence to discharge. An accuracy of discharge analysis greatly depends on the correlation between spatial resolution and wavelength of topographic vertical curve; and (3) Sufficient resolution is about 1/50 of the wavelength.

Estimation of spatial distribution of evapotranspiration in Korea

NOAA-AVHRR data is used to obtain spatial distribution of evapotranspiration for 5 basins, about 69% of total area of Korea. Amounts of evapotranspiration of these basins are estimated by the Penman method, and NDVI (Normalized Difference Vegetation Index) calculated from NOAA-AVHRR data is utilized to estimate its spatial distribution. Because the NDVI value indicates the activity of vegetations and the NDVI histogram reflects the variation of evapotranspiration, its spatial distribution can be estimated using NDVI. This method will make possible to estimate that of North Korea where meteorological data are unavailable. Keywords: NOAA-AVHRR, NDVI, evapotranspiration, spatial distribution