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United States Department of Transportation United States Department of Transportation

Public Roads - Spring 2019

Spring 2019
Issue No:
Vol. 83 No. 1
Publication Number:
Table of Contents

Internet Watch

Assisting Practitioners with Hydraulic Design

by Eric Brown

The purpose of hydraulic engineering is to design a structure with the proper capacity to divert or remove water from the roadway and pass collected water under the roadway. Designing a hydraulic structure requires knowing how much water is associated with the design storm (hydrology) and calculating the velocity, depth, and type of flow (hydraulics) that must be accounted for.

To help with hydraulic design, the Federal Highway Administration's hydraulic engineering professionals work closely with a software development firm as well as partners and stakeholders at Federal, State, and local agencies to develop and advance hydrologic and hydraulic software applications. These tools perform both routine and complex calculations to improve design efficiency and reliability. One of these applications is the FHWA Hydraulic Toolbox.

The Hydraulic Toolbox is a free, publicly available, stand-alone suite of calculators that assists with analyses for the hydraulic design of transportation infrastructure.

Features of the Toolbox

Specific calculators in the Hydraulic Toolbox address a wide set of design variables and features including rational method hydrology, roadside channel capacity, channel linings, curb and gutter sections, bridge scour analysis, and culvert assessment. The program enables users to perform and save hydraulic calculations in one project file, analyze multiple scenarios, create plots, and generate reports of the analyses. The procedures available in the toolbox are based on methods published in the FHWA hydraulic engineering library of technical reference documents, known as the Hydraulic Design Series (HDS) publications, and Hydraulic Engineering Circular (HEC) publications.

The Hydraulic Toolbox has been well received by engineers, designers, and other practitioners.

“The bridge scour tools provide the New Hampshire Department of Transportation [NHDOT] with a consistent means to per-form important calculations,” says Timothy Mallette, a hydraulics engineer with NHDOT's Bureau of Highway Design. “The Hydraulics Toolbox is also a welcome addition to our training program for young engineers.”

Increased Functionality

FHWA continues to expand the toolbox's functionality with new features. One of the latest enhancements is the bridge scour plotting tool. The scour calculator follows the procedures presented in the current (fifth) edition of HEC-18: Evaluating Scour at Bridges (FHWA-HIF-12-003), to assist users with analyses of abutment, pier, and contraction scour as well as long-term channel degradation. The Hydraulic Toolbox can generate a profile plot of the calculated scour components as well as the total scour elevations.

Although the Hydraulic Toolbox primarily functions as a stand-alone program, recent advances in the Surface-water Modeling System (SMS), another FHWA-sponsored hydraulics software program that performs two-dimensional flow analyses, have streamlined bridge scour calculations. SMS is now linked to the Hydraulic Toolbox scour calculator and assists users with determining the hydraulic parameters necessary for scour computations and transferring these parameters to the Hydraulic Toolbox scour calculator. Two-dimensional hydraulic modeling is included in round 5 of Every Day Counts as part of the Collaborative Hydraulics: Advancing to the Next Generation of Engineering (CHANGE) innovation. Visit for more information.

Updated to version 4.4 in July 2018, the toolbox includes a Desktop Reference Guide with the software installation (accessible from the Help button on the top toolbar) to provide important information on the technical features, capabilities, and limitations of the calculators. In addition, the National Highway Institute offers an on-demand, web-based training course for the toolbox, course 135093. The free course takes 3 hours to complete.

The Hydraulic Toolbox, other software applications, and the complete library of HDS and HEC reference manuals are available on FHWA's website at

For more information, contact Eric Brown at

The Hydraulic Toolbox's scour calculator can produce a scour profile plot like this one of components as well as total scour.

Eric Brown is a senior hydraulic engineer on the Geotechnical and Hydraulic Engineering Team in FHWA's Resource Center.