Hec Hms Module

Embed Size (px)

Citation preview

  • 8/3/2019 Hec Hms Module

    1/32

    HYDROLOGIC ENGINEERING USING THE HEC-HMS MODULE

    1 - Theory and Background

    This section consists of a teaching module for undergraduate environmental or civil engineering students.

    The module is structured around three illustrative examples. The students are asked to determine the

    flood potential of a watershed site located in New Jersey. A step-by-step procedure is presented in the

    module in which students are directed to determine rainfall runoff, precipitation, interception/infiltration,

    unit hydrograph, and flood routing. Three illustrative examples are given in this module. The first example

    is the determination of a 100-year flood hydrograph for a New Jersey site. In the second example, the

    students are instructed to route the hydrograph determined in the first example through a given

    reservoir/spillover structure. In the third example the first two examples are repeated by dividing the same

    watershed into multiple watersheds.

    A computer program, "Hydrologic Modeling Systems" (HEC-HMS), developed by the U.S. Army Corps of

    Engineers is used in all of the three examples. This program is used in engineering practice to determine

    the drainage characteristics of both rural and urban watersheds. The use of this program is given in this

    module with instruction on how to prepare the input for the three illustrative examples and the output is

    interpreted. A listing of the program input and output is also given in the module.

    Hydrologic Modeling System (HEC-HMS) is new generation software for precipitation runoff simulation

    that will supersede the HEC-1 Flood Hydrograph Package. HEC-HMS was developed by the U.S. Army

    Corps of Engineers and is a Windows version of HEC-1 with significant advances in computer science

    and hydrologic engineering.

    HEC-HMS contains most of the HEC-1 capabilities, such as flow-frequency curve analysis, snow

    accumulation and melt. Hydraulic features of dam capabilities are underway but have not yet been

    incorporated. The flood damage analysis will be performed by HEC-FDA software and are not included in

    HEC-HMS.

    The HEC-HMS computer model has a large number of options, such as multiple basin watersheds, flood

    damage analysis, etc. The Soil Conservation Service (SCS) TR 55 approach to the determination of

    interception/infiltration and unit hydrographs will be used (TR 55 (1986)). This approach is commonly used

    for urban watersheds by the U.S. Army Corps of Engineers.

    MODEL USERS BACKGROUND

    A description of the HEC-HMS model and its use is given in site examples. There will be little instruction on

    the hydrology to determine the computer model input parameters. The user should have taken a first course

    in Water Resource Engineering where hydrologic and hydraulic techniques are discussed. A number of

    references (Linsley, et. al. (1992), Viessman, et. al. (1989), Hoggan (1989)) are given at the end of this

    module for review purposes.

  • 8/3/2019 Hec Hms Module

    2/32

    RAINFALL RUNOFF SIMULATION

    Simple mathematical relationships are intended to represent model component functions such as

    meteorological, hydrologic and hydraulic processes. These processes are divided into precipitation,

    interception/infiltration, transformation of precipitation excess to sub-basin outflow, addition of base flow and

    flood hydrograph routing. The HEC-HMS model has a number of options for these processes. Refer to the

    illustrative examples for the use and application of each processes.

    PRECIPITATION

    The precipitation model used in the illustrative examples is the frequency-based design storm. This is the PH

    record in HEC-1 hypothetical storms. The 100-year storm frequency is used for all the examples on an

    exceed probability of 1 percent. The storm size is the same as the basin area. The series type is either

    annual or partial. An annual series has been selected. The duration of the maximum intensity is the smallest

    time entered in the duration precipitation list (5 min.) and the storm duration is the longest (24 hours). The

    values of the precipitation for the 5 and 15 minute, and 1, 2, 3, 6, 12, and 24 hour 100 year storm was

    obtained from charts. By entering the chart in references NOAA (1977) and TP 40 (1961) with the latitude of4100 and the longitude of 7425 of Stickle Pond, the precipitation in inches can be determined. Figure 1 is

    a typical chart showing the 24 hour 100-year storm.

    INTERCEPTION/INFILTRATION

    In the HEC-HMS computer model, the land surface interception, depression storage, and infiltration are

    referred to as loss rates. The Soil Conservation Service soil classification system will be used here. The

    SCS has been able to relate the drainage characteristics of soil groups to a curve number, CN. These CN

    values are based on experimentation and experience. The SCS provides information on relating soil group

    type to the curve number as a function of soil cover, land use and antecedent moisture conditions at the

    onset of a storm. Refer to the illustrative examples for the determination of a CN value.UNIT HYDROGRAPH

    The unit hydrograph technique is used in the runoff component of a rain event to transform rainfall excess to

    outflow. A unit hydrograph can be directly input into HEC-HMS or a synthetic unit hydrograph can be

    computed from user supplied parameters (TP 40 (1961), TR 55 (1986), Army Corps. Eng. (1990, 1998)).

    The SCS synthetic dimensionless unit hydrograph method is used in the illustrative examples. A single

    parameter, TLAG, is needed to determine this unit hydrograph. TLAG is equal to the time between the

    center of the excess rain and peak of the unit hydrograph where,

    TLAG = 0.6 x (Time of Concentration).

    An important limitation on the HEC-HMS program is:

    T < 0.29 x TLAG,

    where, T = computation time interval (HMS Control specifications. setup).

    FLOOD ROUTING

  • 8/3/2019 Hec Hms Module

    3/32

  • 8/3/2019 Hec Hms Module

    4/32

    PROGRAM LIMITATIONS AND INSTALLATION

    The following is a list of some of the limitations of Version 2.0 HEC-HMS. Up-to-date information on HEC-

    HMS execution, features, and limitations can be found on the HEC web site, http://www.hec.usace.army.mil .

    The program can also be obtained from this website.

    1. The importing of HEC-1 rainfall data files does not always work.

    2. When printing tables or graphs from within HEC-HMS, output must be directed to a postscript printer.

    3. The currently active screen can be copied to the Windows clipboard by pressing ALT+Print Screen. That

    screen can be "posted" into a document.

    These limitations should be corrected in later versions of HEC-HMS.

    HEC-HMS INPUT PARAMETERS

    To compute an SCS synthetic hydrograph for Stickle Pond the following parameters will be determined.

    WATERSHED AREA

    A topographic map is necessary to delineate a watershed for the study area and calculate its enclosed area.

    Generally a detailed topographic map of the site does not exist. Therefore, U.S.G.S. quadrangle maps of thesite must be obtained. These maps may be purchased from map stores in large cities or from the federal

    government (Geological Survey). Two quadrangle maps: Boonton, NJ, and Newfoundland, NJ, are

    necessary to determine the contributing watershed for Stickle Pond.

    Each quadrangle is identified with a name in the upper right hand corner of the map to help locate the sites.

    The contour interval is printed at the bottom of the map. For the Boonton, NJ and Newfoundland, NJ

    quadrangles, the contour interval is 20 feet.

    Figure 2 is a topographic map of the site. The Stickle Pond watershed is delineated in Figure 3. The area of

    this watershed may be determined with use of a planimeter.

    HYDROLOGIC SOIL CHARACTERISTICSThe SCS curve number loss rate is used to determine the hydrologic soil characteristics for Stickle Pond

    watershed. A soil characteristics map of the site is published in SCS books for each county (Morris County

    for Stickle Pond (SCS (1981))). This book may be obtained from the SCS office in the state or county of

    interest. The soil characteristics map for Stickle Pond watershed is shown in Figure 4. The name and area of

    each of the soils making up this watershed are given in Table 1. A hydrologic classification of each soil may

    be determined from reference TR 55 (1986).

    Antecedent moisture condition (AMC) II was assumed for this analysis. AMC II should be selected unless

    rain records of the site are available. The curve numbers in Table 2 apply for AMC II. For dry conditions

    (AMC I) or wet conditions (AMC III), equivalent curve numbers can be computed (Veissman, Lewis and

    Knapp (1989)).

  • 8/3/2019 Hec Hms Module

    5/32

    PRECIPITATION

    There are six methods of precipitation models available. The gage data is rarely available for small

    watersheds and will not be used for the examples given. The frequency-based storm will be used in the

    illustrative examples. This hypothetical storm will be automatically distributed according to the specified

    depth/duration data. A triangular precipitation distribution is constructed such that the depth specified for any

    duration occurs during the central part of the storm.

    The required inputs are:

    Exceed Probability; storm frequency, the 100-year storm is used for the examples or 1% probability

    Storm Area; storm size will be the same as the watershed area.

    Series Type; annual or partial.

    Duration of Max Intensity; smallest input duration

    Storm Duration; maximum input duration.

    UNIT HYDROGRAPH

    The SCS dimensionless unit hydrograph is used in the illustrative examples. The only parameter necessaryto obtain this unit hydrograph is the Time of Concentration (TC), which is determined by techniques given in

    TR-55 (1986). For the Stickle Pond watershed, there are three components of TC: sheet flow, shallow

    concentrated flow, and open channel flow. See Table 3 for details in the determination of these values.

    EXAMPLE 1: FLOOD HYDROGRAPH

    The flood hydrograph for the Stickle Pond watershed is determined in Example 1. As outlined above the

    frequency based storm will be used to determine the precipitation data, SCS curve number for the loss

    rate, and the SCS unit hydrograph. The determination of these parameters are given in Tables 1, 2 and

    3.

    EXAMPLE 2: FLOOD HYDROGRAPH ROUTINGThe second example is to route a flood hydrograph through a reservoir/spillway complex. The same site,

    Stickle Pond, is selected. Water is retained in Stickle Pond by a dam at its southeastern end. Two spillways

    are available to prevent overtopping of the dam during periods of excess inflow to the reservoir, see Figure 5.

    The main spillway (22.75 feet long) is spanned by a concrete walkway. Three piers support this walkway,

    thus subtracting from the spillway length. A secondary spillway (a clear 12 foot long span) is at a higher

    elevation, 792.05 feet; than the main spillway at 791.7 feet; so there is a range of water surface elevations

    within which overflow occurs only over the main spillway.

    The dam is breached (overtopped) when the reservoir water surface reaches an elevation of 792.4 feet. It is

    assumed that this constitutes failure of the dam.

    The hydrograph determined in Example 1 will be used as the input discharge into the reservoir. The

    additional input parameters to compute the resulting reservoir volume and elevation and the output discharge

    due to this flood hydrograph are:

  • 8/3/2019 Hec Hms Module

    6/32

    FLOOD ROUTING

    A storage versus output table is determined for the Stickle Pond reservoir/spillway complex. The Stickle

    Pond spillway is shown in Figure 5. As in most routing procedures, the initial routing computation is for a

    water elevation at the crest of the spillway. A volume versus elevation table is determined by calculating

    the area of each contour enclosing the pond/reservoir. The first area is the area of the pond. See Table

    4 for the determination of the storage volumes. The spillway output versus elevation, Table 5, is

    determined by the use of the weir equation (King and Brater (1963)) for the Stickle Pond spillways. The

    output versus elevation table has been calculated for elevations up to 796 ft. At elevation 792.4 feet, the

    dam will overtop. Therefore, there is no need to continue the run. In order to avoid error messages the

    dam was extended to an imaginary top of 796 feet even though the dam top is 792.4 feet.

    EXAMPLE 3: MULTIPLE WATERSHEDS

    Subdivision of the area of a large basin may be necessary because of the size and complexity of the physical

    system. A basin with streams and/or a diverse topography may be divided into smaller components. In this

    section, the model input preparation for a subdivided basin is presented. The Stickle Pond watershed isdivided as shown in Figure 6.

    This watershed may be divided into approximately equal sub-watersheds or sub basins. The watershed

    parameter for the sub basins are given in Table 6. These parameters have been described in examples 1

    and 2. Since Stickle Pond is a small watershed, one precipitation distribution is assumed for both sub basins.

    The base flow will be defined here as the flow which results from releases of water from subsurface storage.

    The input parameters starting base flow discharge (ST), threshold discharge (QR), and rate of recession

    index (RT) are used to model the base flow in the HEC-HMS model. ST represents the initial flow in the river,

    RT is equal to the ratio of the recession limb flow to the recession limb flow occurring one hour earlier and QR

    indicates the flow at which an exponential recession begins on the receding limb of the computedhydrograph.

    The base flow record is used to input the base flow into the HEC-HMS model. Using the Stickle Pond case,

    there are three streams feeding into the reservoir, and hydrograph output is available from Examples 1 and 2

    to estimate the base flow input. The parameters selected will be 5 cfs and 8 cfs for the values of ST for the

    north and south sub basins, respectively, 0.05 for QR (i.e. 0.05 times the peak runoff, recommended in the

    HEC-1 manual) and 0.9 for RT (a typical recession ratio) for both sub basins.

  • 8/3/2019 Hec Hms Module

    7/32

    3 - References

    1. Boonton Quadrangle, New Jersey-Morris County, and Newfoundland Quadrangle, New Jersey-MorrisCounty; U.S. Geological Survey, Washington, D.C.

    2. "Five to 60 Minute Precipitation Frequency For the Eastern and Central United States"; NOAA Technical

    Memorandum NWS HYRDO-35, 1977.

    3. "HEC-1 Flood Hydrograph Package"; U.S. Army Corps of Engineers, Davis, California, 1990.4. HEC-HMS Hydrologic Modeling System, U.S. Army Corps of Engineers, Davis, California, 1998

    5. Hoggan, D.; "Computer Assisted Floodplain Hydrology and Hydaulics", McGraw-Hill, New York, 1989.6. King, H and Brater, E., "Handbook of Hydraulics" McGraw-Hill, New York, 1963.7. Linsley, R., Franzini, J., Freyberg, D., and Tchobanoglous, G.: Water Resource Engineering,

    McGraw-Hill, New York, 1992.8. "Rainfall Frequency Atlas of the United States, Technical Paper 40"; Department of Commerce;

    Washington, D.C., 1961.

    9. Soil Survey of Morris County, New Jersey; Department of Commerce; Washington, D.C., 1981.10. "Urban Hydrology for Small Watersheds", Technical Release 55; Department of Commerce; Washington

    D.C., 1986

    11. Viessman, W., Lewis G., and Knapp, J.; "Introduction to Hydrology"; Harper and Row, New York, 1989.

  • 8/3/2019 Hec Hms Module

    8/32

    TABLE 1

    SOIL TYPES AND CURVE NUMBERS COMPUTATION SHEET

    Soil Description Area* CN Weighted CN(Area x CN)

    WATER Stickle Pond, Hoot Owl Lake, New Pond 28 100 2800

    RsC Rockaway: Rock Outcrop 71.5 75 5362.5RvF Rock Outcrop: Rockaway 31.8 90 2862

    HbC Hibernia: Stony Loam 27.5 70 1925

    RsD Rockaway: Rock Outcrop 23.25 89 2069.25

    RgA Ridgebury: Very Stony Loam 18.5 80 1480

    RpC Rockaway: Very Stony Sandy Loam 17.25 72 1242

    RiB Ridgebury: Extremely Stony Loam 12 81 972

    RrD Rockaway: Extremely Stony Sandy Loam 9.5 76 722

    Cm Carisle Muck 7.75 82 635.5

    Ad Adrian Muck 3 80 240

    PeC Parker-Edneyville:Extremely Stony SandyLoam

    2 70 140

    Wm Whitman: Very Stony Loam 1.5 80 120RsC Rockaway: Rock Outcrop 1.5 83 124.5

    RpC Rockaway: Very Stony Sandy Loam 0.75 72 54

    * Note: Area in arbitrary units Total = 255.8 Total = 20748.75

    (Total Weighted CN)/(Total Area) = CN = 81.11

    TABLE 2

    RUNOFF CURVE NUMBERS

    COVER DESCRIPTION CURVE NUMBERS

    FOR HYDROLOGICSOIL GROUP

    COVER TYPE HYDROLOGICCONDITION

    A B C D

    Pasture, grassland, or range-- continuous forage Poor 68 79 86 89

    Fair 49 69 79 84Good 39 61 74 80

    Meadow, continuous grass, protected from grazing and generallymowed for hay.

    --- 30 58 71 78

    Brush--brush-weed-grass mixture with brush the major element. Poor 48 67 77 83

    Fair 35 56 70 77Good 30 48 65 73

    Woods--grass combination (orchard or tree farm). Poor 57 73 82 86

    Fair 43 65 76 82Good 32 58 72 79

    Woods. Poor 45 66 77 83

    Fair 36 60 73 79Good 30 55 70 77

    Farmsteads--buildings, lanes, driveways and surrounding lots. ---- 59 74 82 86

  • 8/3/2019 Hec Hms Module

    9/32

    TABLE 3

    COMPUTATION SHEET FOR TC, TIME OF CONCENTRATION

    Because of the varied shape and topography of the Stickle Pond watershed, three paths of flow were

    selected to determine TC, see Figure 2. These three paths are located in the top, middle and bottom of

    the watershed. The TR-55 reference 1 is used to determine TC.

    There are three components of TC:

    1. Sheet flow TC1 = .007 (nl).8

    / (P2).5

    s.4

    Where, n = 0.4 woods, L = 150 (L maximum of 300 feet, a smaller value is recommended),

    P2 = 3.25 inches (2 year, 24 hour rain), S = slope of watershed at the divide.

    2. Shallow concentrated flow TC2 = L / 3600v where, v = 16.134s1/2

    ; s = water course slope.

    3. Open channel flow TC3 = L / 3600v where, v = (1.49r2/3

    s1/2

    )/n

    where n = .03 from site visit, TR-55 recommends .05; s = channel slope;

    r = hydraulic radius = .4(TR55).

    4. Total TC = TC1 + TC2 + TC3Path S TC1 L (ft.) DH(ft.) S TC2 L (ft.) DH(ft.) S TC3 Total TC

    Top .060 .317 1600 80 .050 .123 4400 78.3 .0178 .339 .779Middle .0313 .411 4900 125 .026 .523 2000 68.3 .0342 .111 1.045Bottom .224 .187 3400 272 .080 .207 3200 19.3 .0060 .425 .819

    The largest value of the time of travel is usually selected for TC. But because of the number of

    assumptions made in selecting the parameters, an average TC will be used.

    TC = 0.88 hours and, TLAG = 0.6 x TC = 0.53 hours

    TABLE 4

    STORAGE CAPACITY

    Drainage area: 1682.5 ac Stickle Pond area: 124ac

    Small islands in Pond: 2.8 ac (included in Pond area)

    New Pond & Hoot Owl Lake: 18 ac Area of 800 ft. contour: 204 ac

    Assuming linear spread from 791.7 Pond elevation to 800 ft. contour. Therefore,

    204 - 124 = 9.639 ac/ft, and the volume = Z (A1 + A2)

    800 - 791.7 2

    ELEVATION AREA VOLUME CUM. VOLUME(ft) (ac) (ac-ft) (ac-ft)

    791.7 124.0 0.0 0.0791.8 125.0 12.5 12.5791.9 125.9 12.5 25.0792.0 126.9 12.6 37.6

    793.0 136.5 131.7 169.3794.0 146.1 141.3 310.6795.0 155.8 151.0 461.6

    796.0 165.4 160.6 622.2

  • 8/3/2019 Hec Hms Module

    10/32

    TABLE 5

    SPILLWAY CAPACITY

    Use the weir equation Q = CL H1.5

    where Q = discharge over the spillway

    L = length of spillway (adjusted for pier-edge effects)

    H = water height above the spillway crest

    Take C = 3.39 (H:V 5:1) (King and Brader (1963) Table 5.11)

    1. Primary spillway Crest 791.7 ft. el.; length = 22.75 ft. with 3 piers

    L = 22.75 - 0.8(H)

    2. Secondary Crest 792.05 ft. el.; length = 12 ft.

    L = 12 - 0.2H

    3. Reservoir Crest 792.4 ft. el.

    Primary Spillway Secondary Spillway

    Elevation H L Q H L Q Total Q

    [ft.] [ft.] [cfs] [ft.] [ft.] [cfs] [cfs]

    791.7 0.0 22.75 0.00 0.00 12.00 0.00 0.00

    792.0 0.3 22.51 12.54 0.00 12.00 0.00 12.54

    793.0 1.3 21.71 109.09 0.95 11.81 37.07 146.16

    794.0 2.3 20.91 247.26 1.95 11.61 107.17 354.43

    795.0 3.3 20.11 408.68 2.95 11.41 195.98 604.66

    796.0 4.3 19.31 583.69 3.95 11.21 298.33 882.02

    TABLE 6

    SUB BASIN CHARACTERISTICS

    Sub Basin Tc (hours) Area (Square miles) CN 100 yr Precip (in)

    North 0.77 0.771 85.2 7.5

    South 0.9245 1.859 79.4 7.5

  • 8/3/2019 Hec Hms Module

    11/32

    Figure 1: One-hundred year, 24-hour rainfall

  • 8/3/2019 Hec Hms Module

    12/32

    Figure 2: USGS Topographic Map of Stickle Pond Figure 3: Stickle Pond Watershed & TC Computation Paths

  • 8/3/2019 Hec Hms Module

    13/32

    A

    A

    5-7 6 ft. 1 in.5-65-7

    5

    1 SECTION A - A

    El. 791.7ft.

    TOP DAM El. 792.4ft.

    Figure 5: Diagram and Cross Section of Primary Spillway

    Figure 4: Soil Survey of Stickle Pond Watershed

  • 8/3/2019 Hec Hms Module

    14/32

    Figure 6: Stickle Pond Sub basins & TC Computation Paths

  • 8/3/2019 Hec Hms Module

    15/32

    4 - Example 1: Flood Hydrograph

    A flood hydrograph will be determined for a rural watershed in this example.

    1. Start HEC-HMS by choosing HMS from the Programs item on the Windows Start Menu. The main

    HEC-HMS windows will appear on screen (Figure 7).2. Using the mouse select New Project from the File pull down menu in the main HEC-HMS window

    (Figure 7).

    Figure 7: HEC-HMS Main Window

    3. Enter a name for the project and an optional description. The program will automatically choose a

    location for the project files, although this may be changed by clicking the Directory Select button.

    For this example, the name of the project is Stickle Pond. Press OK to continue, or Cancel to start

    over.

    4. The program defaults are selected during installation. This example uses the English system of units.

    Verify that the English system is selected by choosing Default Preferences from the Options pull

    down menu in the main HEC-HMS window, and selecting English in the Units section. Choose OK to

    continue.

    5. Choose Basin Model from the Component pull down menu in the main HEC-HMS windows, then

    select New. The New Basin Model dialog box will appear on screen. Press OK to accept the default

    name for the basin. Optionally, you may enter your own name and a description in this dialog box

    before pressing OK. The HMS Basin Schematic window will appear on screen.

    6. Create a subbasin by clicking on the Subbasin button, and while still holding down the mouse button,

    dragging the cursor to the center of the Basin Schematic window and releasing the mouse button. A

    subbasin icon will be created in the Basin Schematic window (Figure 8).

  • 8/3/2019 Hec Hms Module

    16/32

    Figure 8: Basin Schematic Window

    7. Edit the characteristics of the subbasin by double clicking the subbasin icon just created. The

    Subbasin Editor window will appear (Figure 9). Enter 2.629 sq. mi. as the subbasin area. In the Loss

    Rate tab, change the Method to SCS Curve No. Enter 0 for Initial Loss (assuming no loss for this

    example) and % Impervious and 81.11 for SCS Curve No.

    Figure 9: Subbasin Editor Window

    8. Select the Transform tab in the Subbasin Editor window and change the Method to SCS. Enter 0.53

    hours for the SCS Lag (change the Lag time units from the pull down menu). Choose OK to accept

    and save the data. You will now be returned to the Basin Schematic window. The subbasin editor

    will then prompt you to confirm the changes made to the old Loss Rate method. Click OK and then

    continue.

    9. Choose Close from the File pull down menu. You will be prompted to save changes. Accept the data

    by choosing Save Changes. You will be returned to the main HEC-HMS window.

    10. Select Meterelogical Model from the Component pull down menu in the main HEC-HMS windows,

    then select New. The New Precipitation Model dialog box will appear on screen. Press OK to accept

  • 8/3/2019 Hec Hms Module

    17/32

  • 8/3/2019 Hec Hms Module

    18/32

    Figure 10: Completed Precipitation Data Window

    Figure 11: Completed Control Specifications Dialog Box

  • 8/3/2019 Hec Hms Module

    19/32

    15. You will be returned to the main HEC-HMS window. Save the project by selecting Save Project from

    the File pull down menu.

    16. To execute a run, double click on Basin 1 in the main window. The Basin Schematic window of

    Figure 8 will appear. Choose the components to be analyzed by selecting Run Manager from the

    Simulate pull down menu. The Run Manager dialog box will appear on screen (Figure 12). Click on

    Run Configuration from the Simulate pull down menu and the Run Configuration dialog box will

    appear (Figure 13). Choose Basin 1, Precip 1 and Control 1 from the Basin ID, Precip ID and Control

    ID lists. The program automatically assigns a Run ID, however the user can optionally change the

    Run ID. For this example, the default value of Run 1 will be kept. Click Apply and Close to accept

    the components and return to the Simulation Manager dialog box (Figure 12). For this example, there

    is only one basin model, one precipitation model and one control specification and the program

    automatically selects these as defaults. Therefore, this step is performed automatically by the

    program and is not actually necessary. However, the program is capable of storing more than one

    basin model, precipitation model or control specification per project. The user can mix and matchamong the different models, however each run MUST have one basin model, one precipitation model

    and one set of control specifications selected.

    17. Execute the run by clicking on the Compute button (Figure 12). The program will then perform the

    analysis. The HMS Compute dialog box will appear, informing you of the progress of the run. When

    complete, it will display Compute Successful. You can view a log of any errors, warnings and notes

    by pressing View Log. Press Close to continue. You will be returned to the Simulation Manager

    dialog box. Press Close again to be returned to the Basin Schematic window.

    Figure 12: Simulation Manager Dialog Box

  • 8/3/2019 Hec Hms Module

    20/32

    Figure 13: HMS Run Configuration Dialog Box

    18. To view the computation results, click and hold the right mouse button while the cursor is positioned

    over an element in the Basin Schematic window (for this example, there is only one element,

    Subbasin 1). A pop-up menu will appear on screen. While still holding the right mouse button, move

    the cursor down to View Results on the pop-up menu. A new pop-up menu will appear (Figure 14).

    When this menu appears, release the right mouse button and move the cursor on to the new menu.

    19. Select Graph from the pop up menu to view the hydrograph for the subbasin. The hydrograph will

    appear on screen (Figure 15). The hydrograph may be printed by clicking the Print button. When

    done viewing the hydrograph, press Close to return to the Basin Schematic window.

    20. Repeat Step 18, then select Summary Table on the pop-up menu. A summary of the run results will

    appear (Figure 16). Click on Print to print out the results and Close to return to the Basin Schematic

    Window.

    21. Repeat Step 18, selecting Time Series Table on the pop-up menu. A table detailing the precipitation,

    loss, excess, direct flow due to precipitation, baseflow (0 for this example, see Example 3 for a run

    with baseflow) and total flow for each interval appears (Figure 17). Click on Print to print out theresults and Close to return to the Basin Schematic Window.

  • 8/3/2019 Hec Hms Module

    21/32

    Figure 14: Basin Schematic Window with pop-up menus

    Figure 15: Output Hydrograph

  • 8/3/2019 Hec Hms Module

    22/32

    Figure 16: Summary Table

    Figure 17: Time Series Table

    The peak discharge is 4378.5 cfs, occurring 12.6 hours after the start of the storm as given in the

    Summary of Results Table (Figure 16). The runoff hydrograph is given in Figure 15 with a graph of

    the precipitation in gray and loss in inches in black. The difference between the precipitation and loss

    is the excess runoff in inches. A portion of a table of precipitation, loss, excess runoff, direct Q,

    baseflow (no baseflow input for Example 1) and total Q (the sum of the direct Q and baseflow values

    are plotted in the hydrograph, Figure 15) is given in Figure 17 for 6 minute intervals. The remaining

    part of this table is basically the same (Figure 17).

  • 8/3/2019 Hec Hms Module

    23/32

    5 - Example 2: Flood Hydrograph with Routing

    In Example 2, the flood hydrograph from Example 1 will be routed through a reservoir spillway structure.

    There will be two methods shown in example 2. The first is to assume Example 1 has been run. The

    second assumes no data has been entered for the basin.

    METHOD 1

    1. In the main HEC-HMS window, choose Open Project from the File menu and open the project

    created in Example 1: Flood Hydrograph. The Open Project dialog box will appear. Click on the

    project created in Example 1, then click on the Open button. Double click on Basin 1 under Basin

    Model to open the basin model. The Basin Schematic window will appear. Choose Save Basin

    Model As from the File pull down menu. Enter Basin 2 in the New Basin Model field and press OK.

    The Basin Schematic window will appear on screen, set to Basin 2, which is an exact copy of Basin 1.

    2. In the Basin Schematic window, select Basin Model Attributes from the File pull down menu. The

    Basin Model Attributes dialog box will appear on screen. If the Channel Routing field in Default

    Methods is not set Modified Puls, click the down arrow next to the field and select Modified Puls.

    Press OK to be returned to the Basin Schematic window.

    3. In the Basin Schematic window, click on Reservoir button and, while still holding the mouse button,

    drag the cursor to a point below Subbasin-1, and release. A reservoir icon will be created in the

    Basin Schematic window.

    Figure 18: Basin Schematic Window with Routing

    4. Click on the Subbasin-1 icon. Then click and hold the right mouse button while the cursor is

    positioned over the Subbasin-1 icon. A pop up menu will appear on screen. While still holding the

    right mouse button, move the cursor down the menu to Connect Downstream, then release the

  • 8/3/2019 Hec Hms Module

    24/32

    button. The cursor will become a set of crosshairs. Click on Reservoir-1. A line will be drawn

    between Subbasin 1 and Reservoir-1. By this procedure, the direction of flow will be from Subbasin

    1 to the reservoir (Figure 18).

    5. The characteristics of the reservoir are edited by double clicking the Reservoir-1 icon. The Reservoir

    Routing window will appear on screen (Figure 19). Under Input Options, select Elevation-Storage-

    Outflow. You will be prompted as to whether you want to change the table type. Press OK when

    prompted.

    6. Enter the elevation, storage and outflow data as indicated in Tables 4 and 5 (Figure 19).

    Figure 19: Completed Reservoir Routing Window

    7. Press OK. You will be returned to the Basin Schematic window.

    8. Select Run Manager from the Simulate pull down menu. Next, click on Run Configuration from the

    Simulate pull down menu and the HMS Run Configuration dialog box will appear on screen (Figure

    20). Choose Basin 2, Precip 1 and Control 1 from the Basin ID, Precip ID and Control ID lists. Click

    Add and then Close to be returned to the Simulation Manager. Click on Run 2 under Run ID. Click

    on the Compute button to complete the run.

    9. Display the results for Subbasin-1 by clicking on Subbasin-1 and then following steps 18 through 21

    from Example 1: Flood Hydrograph.

    10. To review results, repeat step 9 for Reservoir-1.

  • 8/3/2019 Hec Hms Module

    25/32

    Figure 20: HMS Run Configuration dialog box

    METHOD 2

    1. Repeat steps 1 through 12 from Example 1.

    2. Repeat steps 3 through 8 from Method 1 in this example.

    3. To review results, repeat steps 18 through 21 from Example 1.

    4. To review results, click on the Reservoir-1 icon in the Schematic window and repeat steps 18

    through 21 from Example 1.

    The inflow hydrograph is the same as Example 1 since all the input variables are the same. The peak

    outflow is 599.72 cfs and peaks at 14.7 hours into the storm, or 2.1 hours after the peak inflow (Figure

    21). The elevation in the pond peaked at 794.98 feet (Figure 21). The time of the maximum storage was

    14.7 hours, the same time as the maximum outflow. Since the calculated maximum elevation (794.98

    feet) is greater than the elevation of the top of the dam (792.4 feet), the dam will overtop. The inflow and

    outflow hydrographs are given at the bottom of Figure 22 and the reservoir surface water elevation and

    storage volume at the top of Figure 22. A portion of the table with the reservoir storage, elevation, inflow

    and outflow every 6 minutes is given in Figure 23.

  • 8/3/2019 Hec Hms Module

    26/32

    Figure 21: Summary Table

    Figure 22: Hydrograph for Reservoir-1

  • 8/3/2019 Hec Hms Module

    27/32

    Figure 23: Time series table

  • 8/3/2019 Hec Hms Module

    28/32

    6 - Example 3: Multiple Watersheds

    The same watershed given in Example 2 will be divided to create multiple watersheds discharging into a

    reservoir. This flow will also be routed over the same spillway given in example 2.

    1. In the main HEC-HMS window, choose Open Project from the File menu and open the projectcreated in Example 1: Flood Hydrograph. Choose Basin Model from the Edit pull down menu in the

    main HEC-HMS windows, then select New. The New Basin Model dialog box will appear on screen.

    Press OK to accept the default name for the new basin model, which should be Basin 3. The HMS

    Basin Schematic window will appear on screen.

    2. Create the first subbasin by clicking on the Subbasin button, and while still holding down the mouse

    button, dragging the cursor near the center of the Basin Schematic window and releasing the mouse

    button. A subbasin icon, named Subbasin-1, will be created in the Basin Schematic window.

    3. Repeat step 2, placing Subbasin-2 to the right of Subbasin-1.

    4. Create a junction by clicking on the Junction button, and while still holding down the mouse button,

    dragging the cursor below the two subbasins and releasing the button.

    5. Create a reservoir by clicking on the Reservoir button, and while still holding down the mouse button,

    dragging the cursor below Junction-1 and releasing the button.

    6. Click on the Subbasin-1 icon. Then click and hold the right mouse button while the cursor is

    positioned over the Subbasin-1 icon. A pop up menu will appear on screen. While still holding the

    right mouse button, move the cursor down the menu to Connect Downstream, then release the

    button. The cursor will become a set of crosshairs. Click on Junction-1. A line will be drawn

    between Subbasin 1 and Junction-1.

    7. Repeat step 6, connecting Subbasin-2 to Junction-1.

    8. Repeat step 6, connection Junction-1 to Reservoir-1. The Basin Schematic window should look like

    that pictured in Figure 24 (the names of the basins will be changed in steps 9 and 12). Using this

    procedure, the flow direction goes from the subbasins to the juncture to the reservoir. The reason to

    have a juncture in this example is to have a separate record of the combined flows. The junction can

    be eliminated by directing the flow from the subbasins to the reservoir.

    9. Double click on Subbasin-1. The Subbasin Editor window will appear. Change the name of

    Subbasin-1 to North. Enter 0.771 sq. mi. as the subbasin area. In the Loss Rate tab, change the

    Method to SCS Curve No. Enter 0 for Initial Loss and % Impervious and 85.2 for SCS Curve No. You

    will now be returned to the Basin Schematic window. The Subbasin Editor will then prompt you to

    confirm the changes made to the old Loss Rate method. Click OK and then continue.

    10. Select the Transform tab in the Subbasin Editor window and change the Method to SCS. Enter 0.462

    hours for the SCS Lag (change the Lag time units from the pull down menu).

  • 8/3/2019 Hec Hms Module

    29/32

    11. Select the Baseflow tab from the Parameters tab and change the Method to Recession if it is not

    already selected. Enter the Initial Q of 5 cfs, Recession Ratio of 0.9 and Threshold Q of 0.05 cfs in

    the appropriate fields as shown in Figure 25. Choose OK to accept and save the data. You will be

    returned to the Basin Schematic window.

    12. Repeat steps 9, 10 and 11 for Subbasin-2. Change the name of Subbasin-2 to South. The basin

    area for the South basin is 1.859 sq. mi., the Initial Loss and % Impervious is 0, the SCS Curve No. is

    79.4, the SCS Lag is 0.5547 hours, and for the baseflow, the Initial Q is 8 cfs, the Recession Ratio is

    0.9 and the Threshold Q is 0.05 cfs.

    Figure 24: Basin Schematic Window with Multiple Watersheds

  • 8/3/2019 Hec Hms Module

    30/32

  • 8/3/2019 Hec Hms Module

    31/32

    15. Display the results for the North basin by clicking on North and then following steps 18 through 21 (to

    view results) from Example 1: Flood Hydrograph.

    16. To review results, repeat step 15 for the South basin, Junction-1 and Reservoir-1.

    Figure 27 shows the three inflow hydrographs, North basin, South basin and their combined flows.

    The outflow hydrograph and storage elevation is not shown because it is basically the same as in

    Example 2. The only difference in the format of the output in Example 3 is the time series table at the

    juncture (Figure 28), showing the inflow for the North and South basins with the combined flow. Note,

    the inflows include the baseflow for each basin.

    Figure 27: Outflow Hydrographs

  • 8/3/2019 Hec Hms Module

    32/32

    Figure 28: Time series table at juncture