A GIS-Based Flood Forecasting Model for the Duffins Creek Watershed, Ontario by C. Darren Sutton A Research Paper Presented to Ryerson University in partial fulfillment of the requirements for the degree of Master of Spatial Analysis A joint program with the University of Toronto Toronto, Ontario, Canada © C. Darren Sutton 2003 Author’s Declaration I hereby declare that I am the sole author of this Research Paper I authorize Ryerson University to lend this Research Paper to other institutions or individuals for the purposes of scholarly research. C. Darren Sutton ii Abstract Organizations such as the Toronto and Region Conservation Authority (TRCA) could benefit from a flood forecasting method that uses GIS tools and spatial data because they have already invested in GIS software. This research project utilized a 30- metre resolution Digital Elevation Model (DEM), shapefiles of land cover and soil type, and a Landsat 7 Enhanced Thematic Mapper (ETM+) satellite image to delineate hydrological response units. Snowpack depths were simulated using data from The Weather Network and modelling using the Guelph All-Weather Storm Event Runoff (GAWSER) equations. The Curve Number Method was used to predict peak discharge and time to peak discharge. Snowpack depth was overestimated in some cases, which is likely due to error in snowfall simulations and underestimation of the melt factor. A systematic error, which was caused by averaging of rainfall inputs was corrected for by reducing simulated peak discharge by a factor of 10. The model is most adept at simulating peak discharge for a 71.6 mm rainfall event. For smaller events, a multiplier was introduced to improve the model’s performance. Snowpacks did not have a significant impact on peak discharge although runoff increased slightly. Underestimation of time to peak for some simulations is due to the effects of tillage and error in estimation of channel flow velocity. Despite some errors, a workable model was obtained that could be useful to organizations like the TRCA. iii Acknowledgements I would like to thank my graduate faculty advisor, Dr. Wayne Forsythe for his valuable advice and assistance during the course of this research and throughout my studies as a Master of Spatial Analysis student. I would also like to thank Dr. Shuguang Wang, the program’s current director and outgoing director Dr. Marie Truelove. I am particularly indebted to Dr. Truelove for arranging a practicum position with the Toronto and Region Conservation Authority (TRCA). My experience at the TRCA was instrumental to the completion of this research. Dr. James Li (Civil Engineering) provided valuable advice on a systematic error encountered during model validation. Additionally, my MSA classmates provided advice and encouragement on many occasions. During my practicum with the TRCA I was supplied with data, advice and assistance which were all helpful towards the completion of this research. I would like to thank the following individuals: Hendrik Amo, Geomatics Specialist, Information Systems/Information Technologies who also supervised my practicum; Donald Haley, Water Resources Engineer, and; Jason Tam, Geomatics Specialist, Information Systems/Information Technologies TRCA data was used for this research in accordance with a Memorandum of Understanding signed by both Ryerson University and the TRCA. Digital iv Orthophotographs were used by permission via a Data Release Agreement signed by the author and a Ryerson University library representative. v Table of Contents Author’s Declaration-------------------------------------------------------------------------- ii Abstract---------------------------------------------------------------------------------------- iii Acknowledgments--------------------------------------------------------------------------- iv List of Tables--------------------------------------------------------------------------------- viii List of Figures-------------------------------------------------------------------------------- xi List of Acronyms----------------------------------------------------------------------------- xiii Chapter 1: Introduction-------------------------------------------------------------------- 1 1.1 Flood Forecasting Theory--------------------------------------------------------------- 4 1.1.1 The Curve Number Method--------------------------------------------- 5 1.1.2 Travel Time--------------------------------------------------------------- 6 1.1.3 Snow Infiltration Modelling-------------------------------------------- 10 1.2 Study Area------------------------------------------------------------------------------- 14 1.2.1 Surficial Geology-------------------------------------------------------- 16 1.2.2 Land Cover--------------------------------------------------------------- 18 1.2.3 Population---------------------------------------------------------------- 20 1.3 The Problem --------------------------------------------------------------------------- 20 1.3.1 Objectives----------------------------------------------------------------- 22 1.3.2 Software------------------------------------------------------------------- 22 Chapter 2: Literature Review ----------------------------------------------------------- 24 2.1 Review of Flood Forecasting Software ---------------------------------------------- 24 2.1.1 TOPMODEL ------------------------------------------------------------- 24 2.1.2 GIBSI ---------------------------------------------------------------------- 27 2.1.3 MMS ----------------------------------------------------------------------- 27 2.1.4 PCRaster------------------------------------------------------------------ 28 2.1.5 SWMM--------------------------------------------------------------------- 30 2.1.6 WMS ----------------------------------------------------------------------- 30 2.2 Integration of GIS, Remotely Sensed (RS) Data and Flood Forecasting Models ------------------------------------------------------------------------------------- 31 2.2.1 GIS Inputs ----------------------------------------------------------------- 31 2.2.2 Remotely Sensed Imagery Inputs -------------------------------------- 35 2.3 Use of the Curve Number Method ---------------------------------------------------- 36 2.4 Effects of Tillage on Rainfall and Snowmelt Runoff ------------------------------- 36 Chapter 3: Methodology ------------------------------------------------------------------ 38 3.1 Watershed Model Development ------------------------------------------------------- 38 3.1.1 HEC-GeoHMS Watershed Pre-Processing -------------------------- 38 3.1.2 Land Cover and Soil Type ---------------------------------------------- 42 vi 3.1.3 Ground Cover and Tillage Practices --------------------------------- 44 3.1.4 Curve Number Distribution -------------------------------------------- 49 3.2 Calculation of Travel Time ------------------------------------------------------------ 50 3.2.1 Overland Flow ----------------------------------------------------------- 50 3.2.2 Channel Flow ------------------------------------------------------------ 53 3.3 Parameters for GAWSER Model ------------------------------------------------------ 59 3.3.1 Simulating Mean Daily Temperature --------------------------------- 61 3.3.2 Simulating Snowfall and Rainfall ------------------------------------- 63 3.4 Summary of Assumptions -------------------------------------------------------------- 64 Chapter 4: Results and Discussion ------------------------------------------------------ 68 4.1 GAWSER --------------------------------------------------------------------------------- 68 4.1.1 Calibration of Snowfall and Rainfall Depths ------------------------ 68 4.1.2 Weather Simulation ----------------------------------------------------- 69 4.1.3 GAWSER Snowpack Estimation --------------------------------------- 73 4.2 Accuracy Assessment of Stream Discharge Simulations -------------------------- 75 4.2.1 Model Calibration and Validation ------------------------------------ 75 4.2.2 Sources of Error --------------------------------------------------------- 79 4.2.3 Runoff from Snowpack -------------------------------------------------- 82 4.3 Prediction of Inundated Areas --------------------------------------------------------- 84 Chapter 5: Summary and Conclusions ------------------------------------------------ 88 References ----------------------------------------------------------------------------------- 95 vii List of Tables Table 1.1: Curve Number Definitions 7 Table 1.2: n Values for Sheet Flow 8 Table 1.3: n Values for Channel Flow 10 Table 1.4: Melt/Refreeze Factors for Halton Region, Ontario 12 Table 1.5: Surficial Geology in the Duffins Creek Watershed 16 Table 1.6: Land Cover in the Duffins Creek Watershed 18 Table 3.1: Curve Numbers in the Duffins Creek Watershed 52 Table 3.2: Mean Eight-Point Pour Distance/Direct Distance Ratios for Duffins Creek Watershed 54 Table 3.3: Manning’s Roughness for Calculation of Sheet Flow Travel Time 55 Table 3.4: Peak Discharge and Channel Velocity for Floods on the Creek, Main Branch 57 Table 3.5: Mean Daily Temperatures for Ajax, Ontario, Collected at Pearson International Airport 59 Table 3.6: Climate Normal Data for Ajax, Ontario, Collected at Pearson International Airport 62 Table 3.7: Rainfall Probability Equations for December, January, February and March: Where P is Probability of Occurrence and r is Rainfall Depth (mm) 63 Table 3.8: Snowfall Probability Equations for December, January, February and March: Where P is