Hydrologic and Hydraulic Assessment Tools and Models

Several well-established and accepted public domain tools are available to the practitioner relating to hydrologic and hydraulic assessment.  In addition, there are several proprietary products on the market place that offer additional graphic and computational power that some professionals may find beneficial.  The vast majority of local and state governments allow the use of the major public domain tools, therefore, they are the focus of the write-ups below.  These tools can assist practitioners in the design of stormwater management practices, open channel conveyance systems, flood analysis studies, and other water resources applications.

Hydraulic

HEC-RAS, River Analysis System, Version 3.0 - The HEC-RAS system, developed by the United States Army Corps of Engineers Hydrologic Engineering Center, is intended for calculating water surface profiles for both steady and unsteady gradually varied flow. The system can handle a full network of channels, a dendritic system, or a single river reach.  The model and support documentation can be downloaded for free at http://www.hec.usace.army.mil/.

HY-8, Culvert Analysis, Version 6.1 – HY-8, developed for the Federal Highway Administration (FHWA), automates the design methods described in FHWA publications HDS-5, "Hydraulic Design of Highway Culverts," HEC-14, "Hydraulic Design of Energy Dissipators for Culverts and Channels," and HEC-19, "Hydrology."  The model and support documentation can be downloaded for free at  http://www.fhwa.dot.gov/bridge/hydsoft.htm.

Hydrologic

HEC-HMS, Hydrologic Modeling System, Version 2.1.3 - HEC-HMS is designed to simulate the precipitation-runoff processes of dendritic watershed systems. It is the successor to HEC-1 and provides a similar variety of options but represents a significant advancement in terms of both computer science and hydrologic engineering. In addition to unit hydrograph and hydrologic routing options, capabilities include a linear quasi-distributed runoff transform (ModClark) for use with gridded precipitation, continuous simulation with either a one-layer or more complex five-layer soil moisture method, and a versatile parameter estimation option.  The model and support documentation can be downloaded for free at http://www.hec.usace.army.mil/.

TR-55, Urban Hydrology for Small Watersheds - Technical Release 55 (TR-55) presents simplified procedures to calculate storm runoff volume, peak rate of discharge, hydrographs, and storage volumes required for floodwater reservoirs. These procedures are applicable in small watersheds, especially urbanizing watersheds, in the United States. Limits: NRCS type distributions, 24-hour duration rainfall, 10 subwatersheds, minimum 0.1 hour and maximum 10-hour time of concentration.  The model and support documentation can be downloaded for free at http://www.wcc.nrcs.usda.gov/water/quality/hydro/.

TR-20, Computer Program for Project Formulation Hydrology - Technical Release No. 20 is a physically based watershed scale runoff event model. It computes direct runoff and develops hydrographs resulting from any synthetic or natural rainstorm. Developed hydrographs are routed through stream and valley reaches as well as through reservoirs. Hydrographs are combined from tributaries with those on the main stream stem. Branching flow (diversions), and baseflow can also be accommodated. The model and support documentation can be downloaded for free at http://www.wcc.nrcs.usda.gov/water/quality/hydro/.

SWMM, Stormwater Management Model, Version 4.31 - SWMM is a dynamic rainfall-runoff simulation model, primarily but not exclusively for urban areas, for single-event or long-term (continuous) simulation. Flow routing is performed for surface and sub-surface conveyance and groundwater systems, including the option of fully dynamic hydraulic routing in the Extran Block. Nonpoint source runoff quality and routing may also be simulated, as well as storage, treatment and other best management practices (BMPs). Version 4.3 (May 1994) contains corrections and enhancements to Version 4.20 (June 1992), including a new Transport flow divider, revised hydraulic radius calculations for natural channels in Extran and Transport (to agree with the HEC-2 method), multiple land use options in Runoff, additional sewer infiltration options, improved manipulation of long-term rainfall data (especially 15-min data), a linkage to WASP4 from Transport, additional statistical output from Runoff and many other corrections and enhancements to various program options. Version 4.4 contains many more improvements and options and modifications, and is available in a beta version currently.  The model and support documentation can be downloaded for free at http://www.ccee.orst.edu/swmm/#VERSION%204.4 and http://www.bossintl.com/products/download/item/MIKE+SWMM.html#2, respectively.