Hydrology Part 3: Rational Method Application TSYH 3143

Upon successful completion, the student will be able to:

Module 1 - Review of Hydrologic Equation and Parameters for Rational Method Use

• State and define the primary concepts of the Hydrologic Equation.
• State the rational equation and its units for both metric and imperial use.
• State the requirements in terms of data for rational method use.
• State the limitations of the rational method in terms of area and precipitation event assumptions which are the basis of the method.

Module 2 - Area, Subarea and Runoff Coefficients

• Determine the boundaries of the total catchment area tributary to the point of concentration.
• Assess the catchment area and to divide it into subareas based on the analysis of the characteristics of each subarea.
• Determine and assign appropriate runoff coefficient values to each of the subareas of the total catchment area.
• Utilize two methods to record the area runoff coefficient relationship by determining a mean basin coefficient and to tabulate a runoff coefficient subarea summation table.

Module 3 - Time of Concentration Determination

• State and define the two components of the total time of concentration.
• Select the appropriate saturation time based on the data provided.
• Select the paths for determination of the suitable time of concentration.
• Utilize five methods for determination of the running time.
• Select the method required for a specific catchment area time determination.
• Record the running time path profile and running time calculation summary showing the method used and the calculated results.
• Evaluate the total time of concentration and assess the calculation results in terms of the runoff coefficients in the basin.

Module 4 - Intensity Values and Calculated Flows

• Relate the time of concentration to an intensity of rainfall based on an established intensity duration graph.
• Tabulate the results of the rational method determinations.
• Calculate an initial value for the flood flow at the point of concentration.

Module 5 - FOS, Calculation Review and Design Flow

• Define the terms factor of safety and assess the appropriate safety factor based on the design proposed.
• Complete a review of all factors in the rational equation and assign adjustment values based on this review.
• Calculate a design flow, Qd, based on the results of the review and inclusion of a factor of safety.

Module 6 - Preliminary Culvert Sizing

• Estimate an approximate circular culvert size based on formula, given the appropriate data.
• Estimate an approximate circular culvert size based on nomographs, given the appropriate data.

Effective as of Fall 2003