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Initial Publication Date: May 26, 2015 | Reviewed: November 25, 2019 (see revision history: 2 events)

Rational Method

Abstract

This unit applies a spreadsheet, based on the storm water hydrograph modeling module, that applies the widely utilized Rational Method to estimate hydrographs and flooding for urban watersheds. The specific structure of the model is based on assumptions encoded for Maricopa County, Arizona, which is an urbanized area in the Desert Southwest of the USA, so the model is directly applicable to any similar climate. The model is broadly applicable to urban watersheds anywhere in the world, if appropriate adjustments are made to model parameters and if the necessary input data can be obtained. This model is designed to be utilized in parallel with a modeling guide by the same authors and alongside conceptual instruction in the hydrological concepts of rainfall and runoff processes in undergraduate classrooms. Hydrology and/or computational learning outcomes are assessed using a validated pre/post assessment instrument included with the unit.

Intended Audience

This unit is intended for university students of all levels in hydrology, environmental engineering/sciences and geology/earth sciences.

Conceptual Learning Outcomes

Students demonstrate understanding of the physical causes of flood frequency and intensity, especially the roles of land use and climate.
Students can identify the roles and responsibilities of U.S. Federal hydrology and flood management organizations.
Students demonstrate increased perception of the value of geoscience and hydrology education and information.
Students demonstrate understanding of the utility of mathematical geoscience models, especially for prediction and risk management.

Practical Learning Outcomes

MS Excel and spreadsheet-based calculation and visualization of a simple model
Use of published charts, figures, and tables to obtain design rainfall intensities and frequencies for an urban area
Manual calibration of a simple model to produce results that match observations for an example
Prediction and estimation of the effects of varying a key model parameter on model results

Reference Documents and Files

Concepts Guide for the Unit Concepts Guide for a Unit on Urban Stormwater Hydrograph Modeling with the Rational Method v2 (Acrobat (PDF) 617kB Jun14 13)
Unit Overview Document Unit on Urban Stormwater Hydrograph Modeling with the Rational Method v3 (Acrobat (PDF) 21kB Jun14 13)

Instructions

Please proceed to the first step and develop your rational method model for a watershed of your choice. Starter data for an urban watershed in Arizona is included, but you are encouraged to substitute data for your own place. After developing the model, proceed to the next step where you will learn to calibrate the model to match an observed storm event. As before, a sample storm event is provided for Arizona, but you are encouraged to obtain your own rainfall and runoff data to calibrate your model.

Steps Within This Unit

Assessment

Pre/Post Assessment Rubric: Pre Post Assessment Rubric for Unit on Urban Stormwater Hydrograph Modeling with the Rational Method v3 (Acrobat (PDF) 66kB Jun14 13)

Pre/Post Assessment for Rational Method: Pre Post Assessment for Unit on Urban Stormwater Hydrograph Modeling with the Rational Method v2 (Acrobat (PDF) 69kB Jun14 13)