Flood Inundation Mapping of Tadi River CE 547 GIS in Water Resource Engineering Final Report Submitted By: Aayush Piya May 5, 2017
Contents 1 Motivation & Background... 3 2 Introduction... 3 3 Objective... 3 4 Methods... 4 4.1 Data sources... 4 4.2 Projection used... 4 4.3 Analysis... 4 4.3.1 Delineating Watershed Area... 4 4.3.2 Hydrological Analysis... 5 4.3.3 Flood Inundation Mapping... 5 5 Results... 7 5.1 Watershed Delineation... 7 5.2 Hydrological Analysis... 8 5.2.1 Mean monthly flow and Flow Duration Curve... 8 5.2.2 Rating Curve... 9 5.2.3 Flood Forecast Analysis... 9 5.3 Flood Inundation Mapping... 10 6 Conclusion... 11 7 Future work... 11 APPENDIX
1 Motivation & Background Nepal with its fragile geology, steep slopes, high relief, and variable climates, is prone to water induced disasters such as floods and landslides. Over the last twenty years from 1983-2002, floods and landslides caused 6,466 deaths and more than US $ 200 million in damage. In the absence of information about the nature of flood events, exposure of life and properties and capabilities to cope with disasters, it is difficult to prepare and implement pre-disaster activities. Lack of information is likewise a major constraint in implementing and coordinating the rescue and post-disaster management activities effectively. The necessity of understanding the phenomenon of flooding of the river and to identify and map vulnerable areas for proper management and mitigation of floods is becoming essential to minimize the damages incurred annually. 2 Introduction Flood inundation mapping(fim) is required to understand the affects of flooding in an area and on important structures such as roadways, railways, streets, buildings and airport. FIM provides important information, like depth and spatial extent of flooded zones, required by the municipal authorities to inform the citizens about the major flood prone areas and adopt appropriate flood management strategies. In this Project, the catchment area of a river at site location is determined and a flood inundation map has been developed for the river within the catchment area caused by the 100-year return period flood. 3 Objective The main objective of this project was to explore and learn the basic function of HEC-RAS and HEC-GeoRAS and prepare a flood inundation map using this modelling tools. The specific objectives were as follows: i. Delineate watershed area of a section of Tadi river
ii. iii. Perform Hydrological calculation Use HEC-RAS and HEC-HEC-GeoRAS to develop flood inundation map of the section of river in ArcGIS 4 Methods 4.1 Data sources i. Hydrological data (daily flow records) from the existing Station No. 448 at Tadipul, Belkot, Nuwakot in Tadi Khola published by Department of Hydrology and Meteorology (DHM), Government of Nepal (GoN). ii. Digital Maps of Topography Base Map with Index sheet no. 2785 02B and 2885 14D 4.2 Projection used A modified projection named Nepal Central Projection was used. It is CGS Everest Bangladesh 1937 modified to following parameter. This projection overcomes the inconveniences caused by the negative numbers in Rectangular Coordinate system. Projection: False_Easting: 500000.0 False_Northing: 0.0 Central_Meridian: 84.0 Scale_Factor: 0.9999 Latitude_Of_Origin: 0.0 Linear Unit: Meter (1.0) 4.3 Analysis 4.3.1 Delineating Watershed Area Tadi Khola is located in Rautbeshi, Shikarbeshi and Ghyanphedi Village Development Committees (VDCs) of Nuwakot District in Central Development Region of Nepal. Digital maps were used to determine the catchment area. However, only two digital maps were available which entailed only upper section of the river. Because of unavailability of all the digital maps
only a section of the river was considered for this project. A point with coordinates 85 25 3.48 E and 27 57 45 N was taken as reference to delineate the watershed area. 4.3.2 Hydrological Analysis In this project, the hydrological analysis deals with the flow analysis to obtain the mean monthly flow at the provided point of reference using catchment correlation, flood at different return periods and in short it provides a basis of forecasting. If two basin are hydro-meteorologically similar, data extension may accomplished simply by multiplying the available long term data at the Hydrometric station with the ratio of the basin areas of the base station (proposed site under study) and the index Hydrometric station. In this contest, more accurate results can be obtained using Dicken s formula. Q = Qo A Ao Where, Q and Qo are the discharge at the base and index stations, respectively, and A and Ao are the corresponding basin areas. Using this method, flow duration curve (FDC) and rating curve at the proposed site was developed. For flood frequency analysis Gumbel s extreme value distribution was used. 4.3.3 Flood Inundation Mapping The flood inundation map was developed for a section of Tadi river. For this work, the HEC- RAS was used to calculate water-surface profiles; ArcGIS was used for GIS data processing. The HEC-GeoRAS for ArcGIS was used to provide the interface between the systems. HEC- GeoRAS is an ArcGIS extension specifically designed to process geospatial data for use with HEC-RAS. The extension allows users to create an HEC-RAS import file containing geometric attribute data from an existing digital terrain model (DTM) and complementary data sets. HEC- GeoRAS automates the extraction of spatial parameters for HEC-RAS input, primarily the threedimensional (3D) stream network and the 3D cross-section definition. Results exported from
HECRAS are also processed in HEC-GeoRAS. The general procedure adopted for inundation modelling consists basically of five steps: i) preparation of terrain (DEM or TIN) in ArcGIS, ii) HEC-GeoRAS for pre-processing to generate a HEC-RAS import file, iii) running of HEC-RAS to calculate water-surface profiles, iv) post-processing of HEC-RAS results, and v) floodplain mapping. 4.3.3.1 Data in HEC-RAS The geometric data were imported from HEC-GeoRAS. The imported file includes river streamline along with the bank lines and flow path. The file also includes cross section of the river. Geometric data also requires Manning s roughness coefficient. For simplicity, a constant Manning s coefficient was used. Tadi river is a mountain stream with no vegetation in channel and large boulder at bottom. The n value fitted for this description was 0.04, 0.05 and 0.07 for minimum, normal and maximum respectively. Similarly, for flow data, a constant flow was assumed throughout the stream. A peak flood discharge for 100-year return period was estimated using Gumbel s method. This discharge was used as constant flow for steady flow analysis. For boundary condition, rating curve was used.
5 Results 5.1 Watershed Delineation The total catchment area of the basin at the point of reference was calculated 101Km 2.
Flow, m 3 /s 5.2 Hydrological Analysis 5.2.1 Mean monthly flow and Flow Duration Curve Month Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Mean monthly flow at St. No. 448, m 3 /s 9.63 7.29 5.23 5.62 9.94 34.30 99.15 129.43 92.30 43.22 21.76 13.14 Estimated mean monthly flow at proposed site, m 3 /s 1.52 1.18 0.89 0.93 1.44 5.48 15.33 20.29 14.95 6.81 3.51 2.13 24.00 22.00 20.00 18.00 16.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 FLOW DURATION CURVE 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Exceedence Level Of Flow, %
Stage (m) 5.2.2 Rating Curve Rating Curve 5 4 3 2 1 0 0 25 50 75 100 125 150 175 200 225 250 275 300 Discharge (m3/s) Gauge Height Log. (Gauge Height) 5.2.3 Flood Forecast Analysis Gumbel Parameters Mean (x) 96.20269231 Std deviation(σ) 51.43283741 Reduced Mean (y) 0.532 Reduced stdev s 1.0961 Return Period (yrs) Reduced Variate (yt) Frequency Factor (K) Estimated Discharge (Xt) (m 3 /s) 2 0.366512921-0.150978085 88.43746099 5 1.499939987 0.88307635 141.6218146 10 2.250367327 1.567710362 176.8344844 20 2.970195249 2.224427743 210.6113227 50 3.901938658 3.074481031 254.3319753 100 4.600149227 3.71147635 287.094452 1000 6.907255071 5.816307883 395.35191 2000 7.600652407 6.448911967 427.888533 5000 8.517093183 7.285004272 470.8911326
5.3 Flood Inundation Mapping
6 Conclusion The flood inundation map was developed using HEC-GeoRAS and HEC-RAS. The flood map covered area of 2km 2 with depth ranging from 0 m to 31 m. This project helped to learn basic function of these modelling tools. For any flow analysis, the flow data along with boundary condition are very important. In this project, for simplicity, constant value were used whereas in real life these value changes for each cross section. Selecting proper boundary condition is very important. While developing the inundation map, there were several times that the output polygon for flood area was not continuous. The main cause for this irregularity was found to be cross-section. The cross section is very essential for developing these maps and it is imperative that there is enough cross section provided in the geometric data. 7 Future work While carrying out this project, only a section of the river was considered. It would be very interesting to see how the map develops when whole river is considered for analysis. As mentioned before, constant data such as constant flow and manning s equation were used. An only one boundary condition was applied. In future, this project can be conducted with detailed flow data.
APPENDIX Nepal Index Sheet
Site Location
Hydrological Analysis Mean monthly flow Mean Monthly Data (Correlated) Year: Jan. Feb. Mar. Apr. Hay June July Aug. Sep. Oct. Nov. Dec. Year 1969 1.08 0.69 0.62 0.54 0.50 2.43 11.20 17.01 13.60 5.65 2.77 1.41 4.8 1970 0.94 0.72 0.61 0.49 0.72 4.79 17.63 24.90 13.07 7.41 4.32 2.46 6.5 1971 1.56 1.15 1.03 1.79 2.03 14.06 18.10 21.65 12.79 8.80 4.25 2.20 7.5 1972 1.46 1.33 1.14 1.04 0.94 3.17 17.17 18.25 18.56 7.05 4.75 2.51 6.4 1973 1.59 1.07 1.20 0.81 1.89 12.08 13.94 19.95 19.64 10.12 4.53 2.10 7.4 1974 1.35 0.82 0.55 0.59 0.88 3.85 14.51 25.21 21.50 9.53 4.72 2.91 7.2 1975 2.12 1.70 0.86 0.89 1.05 5.43 18.56 18.25 23.36 8.79 3.67 2.24 7.2 1976 1.69 1.30 0.80 0.95 2.68 7.18 11.94 17.48 15.93 7.28 3.82 1.93 6.1 1977 1.31 1.04 0.75 1.23 1.50 3.19 16.09 23.36 10.32 5.00 2.58 1.58 5.7 1978 1.15 0.86 0.83 0.89 1.76 9.17 26.45 30.93 14.03 8.32 3.40 1.93 8.3 1979 1.29 1.13 0.64 0.73 0.62 2.20 12.16 20.11 10.38 4.42 2.89 2.29 4.9 1980 1.62 1.28 1.14 0.94 1.18 5.92 18.56 24.28 10.29 4.25 2.35 1.53 6.1 1981 1.20 0.93 0.65 1.05 1.39 3.22 13.87 17.94 9.85 3.34 2.30 1.53 4.8 1982 1.15 1.10 0.86 0.85 0.72 2.47 11.04 13.70 8.83 3.31 2.41 1.59 4.0 1983 1.23 0.95 0.80 0.89 1.50 1.75 12.50 14.63 17.94 8.99 4.05 2.54 5.6 1984 1.87 1.32 0.85 0.94 1.90 4.78 16.09 15.93 15.17 4.27 2.64 1.79 5.6 1985 1.40 1.11 0.71 0.68 0.97 3.31 16.09 23.51 21.96 8.60 3.70 2.04 7.0 1986 1.42 1.01 0.62 0.82 1.11 7.59 18.25 16.09 16.40 8.27 3.91 2.63 6.5 1987 1.67 1.40 1.03 1.01 1.10 2.89 15.47 19.33 15.93 8.46 1988 9.28 22.58 26.14 14.40 5.78 3.65 2.55 1989 2.54 1.58 1.18 0.90 2.47 7.38 15.25 26.29 13.73 6.94 3.43 2.06 7.0 1990 1.31 1.39 1.17 1.15 2.04 7.98 17.01 18.56 14.26 7.72 3.63 2.21 6.5 1991 1.75 1.16 0.99 1.06 1.78 4.93 11.01 19.80 14.25 4.52 2.46 1.58 5.4 1992 1.40 1.08 0.48 0.33 0.96 2.91 9.61 18.25 15.47 8.62 4.52 3.06 5.6 1993 2.23 1.87 1.14 1.65 2.91 5.88 12.65 18.25 11.21 5.83 3.31 2.01 5.7 1994 1.69 1.39 1.14 0.81 1.50 4.62 10.90 17.63 15.93 5.69 3.56 2.47 5.6 1995 1.29 1.11 Average: 1.52 1.18 0.89 0.93 1.44 5.48 15.33 20.29 14.95 6.81 3.51 2.13 6.15
Gumbel s Method for Flood Forecast Analysis GUMBEL'S METHOD Year Discharge Order no. (m) Flood Discharge Tp 1969 59.86 1 252.12 27 1970 129.31 2 232.01 13.5 1971 82.6 3 139.21 9 1972 232.01 4 129.31 6.75 1973 252.12 5 126.84 5.4 1974 71.15 6 126.84 4.5 1975 103.63 7 112.91 3.86 1976 34.96 8 103.63 3.38 1977 54.6 9 103.63 3 1978 112.91 10 98.99 2.7 1979 75.79 11 94.35 2.46 1980 126.84 12 89.71 2.25 1981 89.71 13 85.07 2.08 1982 37.9 14 82.6 1.93 1983 126.84 15 79.97 1.8 1984 45.32 16 75.79 1.69 1985 85.07 17 71.15 1.59 1986 139.21 18 68.83 1.5 1987 103.63 19 68.83 1.43 1988 94.35 20 68.83 1.35 1989 79.97 21 59.86 1.29 1990 68.83 22 58.01 1.23 1991 98.99 23 54.6 1.18 1992 58.01 24 45.32 1.13 1993 68.83 25 37.9 1.08 1994 68.83 26 34.96 1.04 Gumbel Parameters Mean (x) 96.20269231 Std deviation(σ) 51.43283741 Reduced Mean (y) 0.532 Reduced stdev s 1.0961
Flow (m³/s) Return Period Reduced Variate (yt) Frequency Factor (K) Estimated Discharge (Xt) 2 0.366512921-0.150978085 88.43746099 5 1.499939987 0.88307635 141.6218146 10 2.250367327 1.567710362 176.8344844 20 2.970195249 2.224427743 210.6113227 50 3.901938658 3.074481031 254.3319753 100 4.600149227 3.71147635 287.094452 1000 6.907255071 5.816307883 395.35191 2000 7.600652407 6.448911967 427.888533 5000 8.517093183 7.285004272 470.8911326 500 Flood Forecast 450 400 350 300 250 200 Gumbel Method 150 100 50 0 1 10 100 1000 Return Period (yrs)
Stage (m) Rating Curve Stage (ft) Flow(cfs) 11.08924 2113.936 13.51706 4566.5396 12.04068 2916.9915 15.74803 8193.3559 16.07612 8903.5338 11.58137 2512.6386 16.07612 3659.6589 9.612861 1234.6008 10.66273 1928.1808 12.79528 3987.3791 11.81102 2676.4986 13.45144 4479.3124 11.05643 3168.0788 10.1706 1338.4259 13.45144 4479.3124 10.5643 1600.4607 12.13911 3004.2187 13.77953 4916.1548 12.79528 3659.6589 12.46719 3331.9388 11.94226 2824.1139 11.48294 2430.7085 12.63123 3495.7989 10.99081 2048.6038 11.48294 2430.7085 11.48294 2430.7085 5 Rating Curve 4 3 2 1 0 0 25 50 75 100 125 150 175 200 225 250 275 300 Discharge (m3/s) Gauge Height Log. (Gauge Height)
Flood Inundation Mapping Geometric Data Data imported from HEC-Geo RAS
Assigning Manning s Roughness Coefficient
Steady Flow Data Assign a constant flow in cfs. Modify Reach Boundary Condition Rating curve was provided in this project.
Photos of site