Kimiteru Sado

Development of flood hazard maps of Bangladesh using NOAA-AVHRR images with GIS

Abstract Flood hazard maps were developed using remote sensing (RS) data for the historical event of the 1988 flood with data of elevation height, and geological and physiographic divisions. Flood damage depends on the hydraulic factors which include characteristics of the flood such as the depth of flooding, rate of the rise in water level, propagation of a flood wave, duration and frequency of flooding, sediment load, and timing. In this study flood depth and “flood-affected frequency” within one flood event were considered for the evaluation of flood hazard assessment, where the depth and frequency of the flooding were assumed to be the major determinant in estimating the total damage function. Different combinations of thematic maps among physiography, geology, land cover and elevation were evaluated for flood hazard maps and a best combination for the event of the 1988 flood was proposed. Finally, the flood hazard map for Bangladesh and a flood risk map for the administrative districts of Bangladesh were proposed.

Flood hazard assessment in Bangladesh using NOAA AVHRR data with geographical information system.

Flooded area and flood hazard assessment in Bangladesh were evaluated using remote sensing (RS) data with the geographical information system (GIS). Image data from the National Oceanographic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) were used to analyse Bangladeshs historical flood event of 1988, which sets a hundred-year record for the inundated areas, with severe damage occurring throughout this region. Cloudy skies often occur during big floods, and visible and infrared rays observed by the NOAA AVHRR cannot penetrate cloud cover. We therefore proposed a new algorithm for classifying cloud covered pixels into water or non-water categories. In order to estimate the flooded area accurately, the images taken during the flood and dry season which were classified into water and non-water categories were superimposed. A new flood hazard map, created from the land cover category and elevation height data which were ranked by flood affected frequency, can be used to evaluate flood risk using only RS data and elevation height data. Copyright

UNSTEADY FREQUENCY ANALYSIS OF PRECIPITATION AT THE 22 METEOROLOGICAL OBSERVATORIES IN HOKKAIDO

We need to discuss that the well-precisely estimate of design rainfalls regarding design high and low water-level of a river is one of the most significant problems. Moreover, we have to consider about to improve the awareness of emergency from disaster for people who live along a river.In this paper, we clarified the non-stationary properties of precipitation by a time series analysis. The sum of trend and period components of each of the 22 meteorological observatories in Hokkaido was shown to have 30%-67% variance of original series. Next, we decided the optimum probability distribution models of the annual precipitation, the annual maximum daily amount of rainfall and the annual maximum number of days with continuous non-rainfall in 17 models by the Standard Least-Squares Criterion. Finally, it was shown that the design rainfall for flood management changes extremely, as a result of the change of the T-year probable hydrological amount and its return period from 1989 to 2004 using the Generalized Extreme Value distribution. Especially, the Okhotsk Sea area indicated to decrease the safety factor for flood management.

NUMERICAL ANALYSIS OF TURBIDITY AND ITS OCCURANCE IN SMALL MOUNTAINOUS BASIN

It is well known that turbidity increases during snowmelt season and storm rainfall of summer season in river flow. Although the reason for the highest degree level of turbidity during snowmelt season is not clear. M.Yamanashi et al. (1995) suggested that the high degree level of turbidity during snowmelt season depends on surface flow on a mountainous basin and the turbidity during summer season is mainly caused by a shearing force between river bed and river flow. There is a possibility to analyze runoff mechanism through the observation of turbidity according his suggestion. The maximum snowmelt which is equivalent to rainfall intensity is about 3 to 4 mm/hr. On the other hand, such rainfall intensity, 3 to 4 mm/hr during summer season does not cause so high turbidity in river flow.This paper studies the mechanisms of the turbidity increase in mountainous river flow through field observations and theoretical analysis. The conditions of turbidity variation by using turbidity occurrence and also inverse estimation method of turbidity occurrence are clarified under the assumption that soil-water content plays an important role.

ESTIMATION OF SPECTRAL REFLECTANCE AND CHLOROPHYLL-A CONCENTRATION OF LAKE ABASHIRI USING NOAA/AVHRR AND SOLAR RADIATION DATA

Lake Abashiri is a brackish lake under the stability of upper oligohaline water and lower polyhaline water. The boundary of two layers has gradually decreased with time. At the same time, this has led to an increase in salinity and eutrophication in the upper layer and to an acceleration of deoxygenation of the lower layer, attributed to occurrence of algal bloom and upwelling of bluish water.In this paper spectral reflectance of water surface was formulated by using NOAA/AVHRR data received in Kitami Institute of Technology, horizontal global and scattered solar radiation. In order to correlate the spectral radiance of NOAA/AVHRR Ch.1 with the spectral radiance emitted from water surface, transmittance and path radiance were calculated approximately by using the horizontal global and the scattered solar radiation. Finally, the chlorophyll-a concentration in the center of Lake Abashiri was estimated by the regression line of the chlorophyll-a concentration on the difference of spectral reflectance between fluorescence and absorption zone of phytoplankton.