An Evaluation of the Height Above Nearest Drainage (Hand) Flood Mapping Methodology with the Implementation of Multivariant Linear Regression Algorithm
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AN EVALUATION OF THE HEIGHT ABOVE NEAREST DRAINAGE (HAND) FLOOD MAPPING METHODOLOGY WITH THE IMPLEMENTATION OF MULTIVARIANT LINEAR REGRESSION ALGORITHM A Thesis Presented By Said Lababidi to The Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Master of Science in the field of Civil and Environmental Engineering Northeastern University Boston, Massachusetts May 2021 ii TABLE OF CONTENTS 1. ABSTRACT ................................................................................................................ v 2. INTRODUCTION ....................................................................................................... 1 3. METHODS .................................................................................................................. 4 3.1 Study Region and Rivers ..................................................................................... 4 3.2 The Height Above Nearest Drainage Methodology ............................................ 5 3.3 Application and Tools ......................................................................................... 8 3.4 Implementation of Multivariant Linear Regression Algorithm ........................ 10 3.5 Trial Definitions ................................................................................................ 12 3.6 Performance Metrics ......................................................................................... 12 4. RESULTS/DISCUSSION ......................................................................................... 14 4.1 Floodplain Analysis .......................................................................................... 14 4.2 Uncertainty Analysis ......................................................................................... 15 4.3 Multivariant Linear Regression Analysis .......................................................... 17 4.4 Visual Analysis and Comparison ...................................................................... 19 4.5 HAND map with Multivariant Linear Regression Implementation .................. 23 5. CONCLUSION ......................................................................................................... 25 6. REFERENCES .......................................................................................................... 25 7. APPENDIX ............................................................................................................... 28 iii LIST OF TABLES Table 1. The combined raster cell values........................…………………………......…12 Table 2. Number of cells in the HAND map with actual 100-year discharge values.........14 Table 3. Number of cells in the HAND map with 25% increase in 100-year discharge values ................................................................................................................................15 Table 4. Number of cells in the HAND map with 25% decrease in 100-year discharge values ................................................................................................................................15 Table 5. Summary of performance metrics for each of the three trials............................. 16 Table 6. The Coefficients of the Multivariant Linear Regression Algorithm....................18 Table 7. Number of cells in the HAND map with Multivariant Linear regression algorithm............................................................................................................................18 Table 8. Comparison of performance metrics for the original HAND map and MLR HAND map........................................................................................................................18 Table A1. Sample data for the 100-year discharges from FIS reports for the 219 reaches................................................................................................................................30 Table A2. The Attributes used for the Multivariant Linear Regression Algorithm..........37 iv LIST OF FIGURES Figure 1. The Study region of Eastern Massachusetts showing three main rivers (Charles river, Neponset river and Mystic river) and their tributaries (626 reaches total) ............... 4 Figure 2. The first step in producing a Height Above Nearest Drainage (HAND) flood map; a catchment raster is created (left) and each cell in the raster is assigned a COMID (right).. ................................................................................................................................ 6 Figure 3. HAND raster generated by determining the difference in elevation between the out-of-stream cells and the in-stream cells.. ....................................................................... 6 Figure 4. The usage of rating curves to determine the stage that corresponds to the 100- year discharge and storing the values in a stage raster. ...................................................... 7 Figure 5. Subtraction of the HAND raster from the stage raster to produce the final flood map ...................................................................................................................................... 8 Figure 6. Comparison between the actual discharges and the predicted discharges for the 22 reaches as the test sample ............................................................................................ 17 Figure 7. Comparison between the three HAND maps and FEMA map for Charles River near Back Bay area. (A) Actual HAND map, (B) HAND map with 25% increase in discharge, (C) HAND map with 25% decrease in discharge.. .......................................... 20 Figure 8. Comparison between the three HAND maps and FEMA map for Charles River near Medfield (231 Km2 total upstream drainage area) . (A) Actual HAND map, (B) HAND map with 25% increase in discharge, (C) HAND map with 25% decrease in discharge... ........................................................................................................................ 21 Figure 9. Comparison between the three HAND maps and FEMA map for Beaver Brook West of Watertown(19.55 Km2 total upstream drainage area). (A) Actual HAND map, (B) HAND map with 25% increase in discharge, (C) HAND map with 25% decrease in discharge... ........................................................................................................................ 22 Figure 10. Comparison between the HAND map with the implemented Multivariant Linear Regression algorithm and FEMA map for four reaches; (A) Eagle Brook, (B) Mine Brook, (C) Rock Meadow Brook and (D) Rosemary Brook... ......................................... 24 Figure A1. Comparison between the three HAND maps and FEMA map for Charles River near Medfield (231 Km2 total upstream drainage area) . (A) Actual HAND map, (B) HAND map with 25% increase in discharge, (C) HAND map with 25% decrease in discharge................................................................................................................………28 Figure A2. Comparison between the three HAND maps and FEMA map for Beaver Brook West of Watertown(19.55 Km2 total upstream drainage area). (A) Actual HAND map, (B) HAND map with 25% increase in discharge, (C) HAND map with 25% decrease in discharge.….......................................................................................................................29 v ABSTRACT An evaluation for the Height Above Nearest Drainage (HAND) flood mapping methodology is presented for three main rivers in Massachusetts and their tributaries. The main rivers are Charles River, Neponset River and Mystic River. We implemented a Multivariant Linear Regression algorithm to predict discharges for some of the rivers’ tributaries due to the lack of discharge data from the Flood Insurance Study (FIS) reports for these reaches. The HAND methodology is a low complexity, terrain based flood mapping method that uses a Digital Elevation Model (DEM), discharge-stage relationship (Rating Curves) and stream flow data. The 100-year discharge data was extracted from FEMA’s FIS reports for each of the three main rivers and some of their tributaries. The rating curves were used for all reaches to determine the water levels (stages). Based on the DEM for the region, we were able to determine the inundated (wet) cell from the non-inundated cells (dry) for the areas around all reaches using ArcGIS and a Python script to generate the flood maps. FEMA’s 100-year flood maps were used in this study as our reference to evaluate the accuracy and the efficacy of the HAND method. The results show that the HAND method tends to underpredict some flooded areas around low order reaches and overpredicts the flooded area around very high order reaches that have high discharges. For medium order reaches, the flooded areas were almost identical to FEMA’s flood maps. vi The implementation of the Multivariant Linear Regression algorithm resulted in a HAND flood map with an accuracy close to the accuracy of the original HAND flood map. That implies that the algorithm is an effective and accurate tool to use for predicting river discharge. 1 2. INTRODUCTION Floods have been considered one of the costliest and most devastating types of disasters in terms of damaging properties and human casualties. Between 1995 and 2015, over 2.2 billion people were affected by floods, comprising 53% of the total of people affected by all weather-related disasters (Mateo-Garcia et al., 2021). Extreme and frequent flood events have devastating