EFH-2 Overview Quan D. Quan Hydraulic Engineer USDA – NRCS – WNTSC 301-504-3952 quan.quan@wdc.usda.gov William H. Merkel Hydraulic Engineer USDA – NRCS – WNTSC 301-504-3956 william.merkel@wdc.usda.gov Introduce yourself. EFH-2 Overview

Training Objectives Upon completion of this training you will: Be familiar with the parameters used in EFH-2. Be able to develop and enter data inputs for the computer program. Be able to run the model and interpret the results. Training Objectives. Upon completion of this training : You will be familiar with the parameters used in EFH-2. As we go along, we’ll review the technical aspects of the hydrologic analyses, but the real focus is on getting you familiar with the computer program, so we’ll only dwell on the hydrology aspects as much as is necessary to define terms and make sure you understand where the information comes from and how it is utilized in the program. You will be able to develop and enter data inputs for the computer program. Again, understand where the information comes from, particularly because you will have to develop a good portion of it yourselves. You will be able to run the model and interpret the results. That is, you will be able to develop the inputs, enter them into the program and run the model. We will also talk about debugging model runs, and interpreting output to help you make the decisions as to whether or not the output is reasonable, and if necessary, make corrections to your data.

Background March 2003 Engineering Field Handbook Chapter 2 Major revision in October, 1990 DOS version 1.2, computer program March 2003 First version of Windows based EFH-2 (EFH-2 version 1.1.0) is released Owen Kvittem, SCE-NE CCE Certification EFM was first issued by the Soil Conservation Service as a graphical method. Graphical in this case meaning a method for using graphs and hand computations. Developed as a simplified method for estimating runoff volumes, peak discharges, and partial hydrographs for small watershed areas. In October 1990 the first version of a EFH-2 computer program was released. This DOS program utilized the same tables and graphs which were developed for the hand computations. Finally, in March 2003 the first version of a Windows based EFH-2 computer program was released.

Program Description Estimating peak discharge (cfs) and runoff depth (inches) Single watershed No hydrograph Simple version of WinTR-55 and WinTR-20 CCE – certified Windows version The EFH-2 software implements the procedures described in the NEH 650 – Engineering Field Handbook, Chapter 2 (EFH-2) for estimating runoff and peak discharge for single watershed. The EFH-2 computer program was written in Visual Basic 6.0.

Capabilities & Limitations The next couple of slides are titled “Capabilities and Limitations.” Represented here are the range of parameters within which EFH-2 is useful. Questions like, “What is the maximum drainage area size for which EFH-2 can be used?” is covered here.

Capabilities & Limitations Drainage Area 1 – 2000 acres Tc for sub-area 0.1 hr < Tc< 10 hrs ARC 2 (average) CN for any sub-area 40 < CN < 98 Number of sub-areas 1 Average slope 0.5-64 percent Watershed length 200-26,000 feet As mentioned previously, many of the capabilities and limitations in EFH-2 were carried over from the original EFM . The result is a model that is fairly simple and straightforward to use.  Drainage area is limited to 1-2000 acres.  Time of concentration for single sub-area is limited to between 0.1 and 10 hours.  Antecedent runoff condition 2 is the assumed antecedent runoff condition. All the runoff curve number tables in EFH-2 are for antecedent runoff condition 2.  Curve number values for one sub-area range from 40 to 98. If a weighted CN of less than 40 is estimated for any one sub-area, use another procedure.  EFH-2 allows the user to model 1 sub-area.  Time of concentration for the sub-area is limited to between 0.1 and 10 hours. This limitation stems from the original TR-55. When the generalized tables and graphs were developed for the original TR-55, they spanned values of Tc ranging from 0.1 to 10 hours.  Average slope length is limited to 0.5 – 64 percent.  The Watershed length is limited to 200-26,000 feet.

Capabilities & Limitations Routing No valley – reservoir Urban land use <10% Rainfall Depth Default or user-defined (range of 0-26 inches) Rainfall Distributions NRCS Type I, IA, II, III, DMV distributions. * Draft distributions are developed for northeast states based on NRCC data. Rainfall Duration 24-hour Dimensionless Unit Standard peak rate factor (484) Hydrograph or DMV 284  No valley or reservoir routing is required.  Urban land use within the watershed does not exceed 10%.  Standard NRCS Rainfall Distribution Types I, IA, II, III and DMV are built-in to the program. Localized rainfall distributions based on NOAA Atlas 14 or NRCC, for example, may be developed through a special study. Rainfall duration is limited to 24 hours for any storm that is modeled using EFH-2. Nothing less than 24-hours can be entered by the User, nor can anything greater than 24-hours be entered.  The standard peak rate factor 484 Dimensionless Unit Hydrograph is the default built-in unit hydrograph utilized by EFH-2. The DMV unit hydrograph may be used if the DMV rainfall distribution is selected.

Capabilities & Limitations Peak discharge is determined by procedures contained in NRCS Engineering Field Handbook, Chapter 2 Information needed to use this procedure: drainage area curve number watershed length watershed slope rainfall amount rainfall distribution A few final thoughts before moving on.  WinTR-55 utilizes methods based on open and unconfined flow over land and in channels. For large events during which flow is divided between sewer and overland flow, more information about hydraulics is needed than is presented here to determine Tc.  Therefore, it is inappropriate for use in closed system pipe flows such as storm sewers.  And finally, calibration is not something done often when making hydrologic analyses using WinTR-55, primarily because most of the watersheds on which WinTR-55 analyses are performed do not have stream gages to which those comparisons can be made. It is suggested however, that at a minimum, some comparison of data against results obtained from USGS curves of peak flow be made. Even though standard errors of estimates for USGS peak discharge equations are often quite high it is a good order of magnitude check.

EFH-2 Team Quan D. Quan Beltsville, MD NRCS Tony Funderburk Fort Worth, TX NRCS Claudia Hoeft Washington, DC NRCS William Merkel Beltsville, MD NRCS These are the names behind the program. This is a listing of all the members of the EFH-2 development team. Feel free to contact members of the team with questions and comments.

Summary Reviewed the background of EFH-2 Gave an overview of EFH-2 capabilities and limitations The objectives for this first lesson were: To review the background of EFH-2; To provide a very brief description of the program; And finally, to give an overview of the EFH-2 capabilities and limitations.

Questions ? Summary Questions?