미계측 하천의 홍수위 해석을 위한 단면 추정 기법 개선

Improvement of Cross-section Estimation Method for Flood Stage Analysis in Unmeasured Streams

Abstract

The objective of this study was to improve the cross-sectional area and height estimation method using stream width. Stream water levels should be calculated together to simulate inundation of agricultural land. However, cross-sectional survey data of small rural rivers are insufficient. The previous study has developed regression equations between the width and the cross-sectional area and between the width and the height of stream cross-section, but can not be applied to a wide range of stream widths. In this study, cross-sectional survey data of 6 streams (Doowol, Chungmi, Jiseok, Gam, Wonpyeong, and Bokha stream) were collected and divided into upstream, midstream and downstream considering the locations of cross-sections. The regression equations were estimated using the complete data. $R^2$ between the stream width and cross-sectional area was 0.96, and $R^2$ between width and height was 0.81. The regression equations were also estimated using divided data for upstream, midstream and downstream considering the locations of cross-sections. The range of $R^2$ between the stream width and cross-sectional area was 0.86 - 0.91, and the range of $R^2$ between width and height was 0.79 ? 0.92. As a result of estimating the cross-sections of 6 rivers using the regression equations, the regression equations considering the locations of cross-sections showed better performance both in the cross-sectional area and height estimation than the regression equations estimated using the complete data. Hydrologic Engineering Center - River Analysis System (HEC-RAS) was used to simulate the flood stage analysis of the estimated and the measured cross-sections for 50-year, 100-year, and 200-year frequency floods. As a result of flood stage analysis, the regression equations considering the locations of cross-sections also showed better performance than the regression equations estimated using the complete data. Future research would be needed to consider the factors affecting the cross-sectional shape such as river slope and average flow velocity. This study can be useful for inundation simulation of agricultural land adjacent to an unmeasured stream.

Fig. 1 Schematic diagram of this study

Fig. 2 Locations of selected streams in this study

Fig. 3 Regression equations between cross-section characterstics

Fig. 4 Regression equations between cross-section characterstics (Shin et al., 2016)

Fig. 5 Scatter plots comparing measured and estimated cross-section characteristics (Doowol stream)

Fig. 6 Regression equation between stream width and cross-sectional area considering locations of cross-sections

Fig. 7 Regression equation between stream width and height considering locations of cross-sections

Fig. 8 Scatter plots comparing measured and estimated cross-section characteristics considering locations of cross-sections (Doowol stream)

Fig. 9 Scatter plots of water surface elevations between measured and estimated cross-sections by 50-year, 100-year and 200-year frequency floods (Doowol and Cungmi stream)

Fig. 10 Scatter plots of water surface elevations between measured and estimated cross-sections considering locations of cross-sections by 50-year, 100-year and 200-year frequency floods (Doowol and Cungmi stream)

Table 1 Characteristics of cross-sections in 6 streams

Table 2 Design floods of different frequency on Doowol stream (m³/s)

Table 3 Equations for statistical performance measures

Table 5 Statistical variances between measured and estimated cross-section characteristics of 6 streams (Doowol, Chungmi, Jiseok, Gam, Wonpyeong, and Bokha)

Table 6 Statistical variances between measured and estimated cross-section characteristics of 6 streams (Doowol, Chungmi, Jiseok, Gam, Wonpyeong, and Bokha) considering locations of cross-sections

Table 7 Variances of water surface elevations between measured and estimated cross-sections for 6 streams (Doowol, Chungmi, Jiseok, Gam, Wonpyeong, and Bokha) by 50-year, 100-year and 200-year frequency floods

Table 8 Variances of water surface elevations between measured and estimated cross-sections considering locations of cross-sections for 6 streams (Doowol, Chungmi, Jiseok, Gam, Wonpyeong, and Bokha) by 50-year, 100-year and 200-year frequency floods