HEC HMS Modeling Report - Sites at LafayetteHEC‐HMS Runoff and Routing Model Stephen Beavan, Melanie DeFazio, David Gold, Peter Mara and Dan Moran CE 421: Hydrology Fall 2010 December

Bushkill Creek 3rd Street Dam Removal Analysis

HEC‐HMS Runoff and Routing Model

Stephen Beavan, Melanie DeFazio, David Gold, Peter Mara and Dan Moran

CE 421: Hydrology

Fall 2010

December 15, 2010

1

Contents 1. Objectives and Tasks ............................................................................................................................. 2

2. Site Description ..................................................................................................................................... 2

3. Methods ................................................................................................................................................ 4

3.1 Sub‐basin Modeling ............................................................................................................................ 5

3.1.1 NRCS Curve Numbers ..................................................................................................... 6

3.1.2 Time of Concentration ................................................................................................... 7

3.1.3 Baseflow ........................................................................................................................................... 8

3.2 Reach Modeling .................................................................................................................................. 8

3.3 Reservoir Modeling ............................................................................................................................. 9

4. Results and Discussion ........................................................................................................................ 13

4.1 Results ............................................................................................................................................... 13

4.2 Limitations ......................................................................................................................................... 15

5. References .......................................................................................................................................... 17

Appendices

Appendix A – Curve Number Tables Appendix B – Time of Concentration Data Appendix C – Baseflow Calculations for Bushkill Creek Appendix D – Reach K‐Value Calculations Appendix E – Flood Stage Areas for 3rd St. Dam Appendix F – Stage Discharge Table Spreadsheet Calculations Appendix G –HEC‐HMS Results

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1. Objectives and Tasks

To determine the effect of removing the 3rd Street Dam on peak flows in the Bushkill Creek, a

model of the Bushkill Creek Watershed and the 3rd Street Dam was created using HEC‐HMS

(ACOE, 2001). In order to use this program, it was first necessary to complete extensive work

within ArcGIS and AutoCAD.

1.1 Objective The goal of this report is to determine the difference in peak outflows, with and without the

presence of the dam, for various design storm hydrographs.

1.2 Tasks

Delineate the Bushkill Creek Watershed, divide into sub‐basins

Determine the land cover, soil type and time of concentration within each sub‐basin

Determine the stage‐storage relationship at the 3rd Street Dam, as well as the stage‐

discharge relationship

Develop an accurate estimation of the Bushkill Creek’s base flow using data from

nearby watersheds

Develop a HEC‐HMS model of the watershed, reaches and reservoir

Rout storm hydrographs with and without the dam

2. Site Description

The Bushkill Creek Watershed encompasses an area of almost eighty square miles. The

watershed and its corresponding topography can be seen in Figure 1.

3

FIGURE 1 ‐ BUSHKILL CREEK WATERSHED (DIGITAL‐TOPO‐MAPS)

The 3rd Street Dam, owned by Lafayette College, is adjacent to the College’s downtown arts

campus. The surrounding area includes scattered woods, but primarily consists of paved

streets and buildings. Lafayette’s main campus sits on the hill above the Bushkill Creek and

drains directly into the creek. Figure 2 shows the area directly upstream of the dam.

FIGURE 2 ‐ LAND UPSTREAM OF 3RD STREET DAM

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Figure 3 and Figure 4 show the dam under both baseflow and stormflow conditions, respectively.

FIGURE 3 ‐ DAM UNDER BASEFLOW CONDITIONS (LYONS, C.)

FIGURE 4 ‐ DAM UNDER STORMFLOW CONDITIONS (BRANDES, D.)

3. Methods

Using HEC‐HMS, storm routing hydrographs were developed for the Bushkill Creek at the site of

the 3rd Street Dam. HEC‐HMS creates a basin model which consists of a system of

interconnected sub‐basins, reaches, junctions and reservoirs (ACOE, 2001). This basin model

was paired with meteorological data to simulate runoff for the 2‐yr through 100‐yr storms.

5

3.1 Subbasin Modeling

ArcGIS was used in the preliminary stages of the project to develop inputs for the HEC‐HMS

sub‐basin models. These inputs include curve number, time of concentration and area. To

obtain these values, it was first necessary to divide the Bushkill Creek Watershed into sub‐

basins. Based on smaller tributaries throughout the Bushkill Creek Watershed, eight sub‐basins

were delineated. The sub‐basins and their given names are shown Figure 5 below. The Belfast,

Forks, and Easton sub‐basins contain reaches of the Bushkill Creek, which were also critical for

the HEC‐HMS model. The HEC‐HMS model basin containing both the sub‐basins and reaches

are shown in Figure 6.

FIGURE 5 – SUB‐BASINS WITHIN THE BUSHKILL CREEK WATERSHED (NOT TO SCALE)

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FIGURE 6 – HEC‐HMS REPRESENTATION OF THE BUSHKILL CREEK WATERSHED

3.1.1 NRCS Curve Numbers

Runoff curve number (NRCS, 1986) depends on land cover and soil type. Within each sub‐basin,

the corresponding land usage (LCI NLCD, 2001) and soil type (LVPC) were determined. In

several cases, the specific land usage of a sub‐watershed was distributed over multiple soil

classifications. The most dominant soil throughout the watershed was used to determine the

inputs for the curve number calculations, except for Nazareth and Forks. For these watersheds,

the percentages of B and C soils were almost equal, so it was necessary to distinguish the land

7

usage within each soil type and weight the corresponding inputs accordingly. The land use

layer used was based off data from the year 2000 and did not account for population growth

and development since that time. From population data for Bushkill municipalities, it was

found that the only significant population growth had occurred in Forks Township, which had

experienced a 52.7% growth in population from 2000 to 2005. In order to account for this, the

developed area in the Forks sub‐watershed was increased by 52.7%. This area was subtracted

from cultivated crops, Forks’ most prominent land cover.

Using the NRCS TR‐55 Curve Numbers, the relative curve number for each watershed was

calculated. The assumptions and full curve number tables can be seen in Appendix A. The

higher curve numbers reflect the amount of developed land in each watershed. Although some

sub‐basins have less developed land, C‐type soils will typically produce larger curve numbers.

The distribution of various land cover and soil types within the Bushkill Creek Watershed can

also be seen in Appendix A. DISCUSS POPULATION GROWTH

3.1.2 Time of Concentration

The time of concentration is the time that is required for water falling on the most remote part

of the watershed to reach the outlet point of the watershed. Time of concentration can be

calculated using the SCS lag method (Mays, 2005).

. 1 .

1900 .

Where: L = length of watershed

S = ⁄

Y = slope of watershed

It was necessary to determine the slope and length of each sub‐basin and reach to ultimately

find the time of concentration. The lengths were determined by tracing polylines along flow

channels in ArcGIS. Sub‐basin slopes were also determined using ArcGIS. Both of these

measurements were based on a 10‐m digital elevation model (DEM) (USGS, 2010).

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The results of the time of concentration calculations can be found in Appendix B.

3.1.3 Baseflow

The baseflow, an important input into the HEC‐HMS watershed model, was estimated using

data from USGS stream gauges on three nearby rivers; Jordan Creek, Monocacy Creek and Little

Lehigh Creek. Mean monthly baseflow data was found on the USGS website. First the flows

were scaled to the Bushkill Creek watershed area. Then the three baseflows were weighted

based on their watershed characteristics. The three watershed characteristics that influenced

the weighting were: the percent carbonate bedrock, percent urban area and percent forested

area. These characteristic values can be found in Appendix C. The percent urban area and

percent forested area for the Bushkill Creek were calculated using the land use data in ArcGIS,

while the percent carbonate bedrock was determined using geological data in ArcGIS. Both sets

of data were from the Lehigh Valley Planning Commission. For each of the creeks, besides the

Jordan Creek, the percent carbonate was the highest percentage out of the three relevant

characteristics. A weight of 0.5 was given to the Little Lehigh Creek because its percent

carbonate was closest to that of the Bushkill Creek, while a weight of 0.4 was given to the

Monocacy Creek. Since the percent carbonate of the Jordan Creek was drastically different

than the Bushkill Creek, a weighting of 0.1 was assigned. Using these weights and the scaled

baseflows, a weighted average monthly baseflow was found. A table illustrating the weighting

of each creek can be found in Appendix C, along with estimated monthly baseflow of the

Bushkill Creek.

3.2 Reach Modeling

The sub‐basins in the HEC‐HMS model are connected by a series of reaches. As the flow moves

down a reach, the peak flow of the storm’s hydrograph is reduced and delayed. The amount

that the peak is diminished and delayed is called “channel routing”. The river reaches were

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routed using the Muskingum method. This method requires a “K value” which is estimated by

the travel time through the reach, K≈L/V. The velocity in the channel was estimated using

Manning’s equation:

1.49 . .

Where:

V = velocity

n = Manning’s n value

Rh = the hydraulic radius

S = the Slope in ft/ft.

Uniform flow was assumed for this equation.

The Manning’s n value was estimated at 0.04 for each reach (Mays, 2005). The Hydraulic

Radius, Rh, was estimated using Google Earth maps and assuming the river channel to be

trapezoidal. The slopes of reaches were calculated using elevations from USGS topographical

maps, as they were found to be more accurate than the DEM.

A table of resulting K values can be found in Appendix D. The Muskingum method also requires

a weighting factor “x”, which was given its typical value of 0.2.

3.3 Reservoir Modeling

3.3.1 Stage Area Relationship

The 3rd Street Dam storage was modeled using the stage‐area relationship determined in

AutoCAD from the survey results. The four largest upstream dams, Lions Park Dam, Crayola

Dam, Rockwood Pigments and Easton Public Works Dam appeared to be of similar size to the

3rd Street Dam, and since no stage‐storage and outflow data were available, the sizing data of

10

the 3rd Street Dam was used throughout. The location of these dams can be seen below in

Figure 7.

FIGURE 7: LOCATION OF UPSTREAM DAMS

Survey points surrounding the dam were found from the “Bushkill Creek Survey Report, Nov

2010”; contour lines from these points were created using AutoCAD Civil 3D to develop the

stage‐area relationship. The contours can be seen below in Figure 8.

FIGURE 8– CONTOURS OF FLOOD STAGES AT DAM LOCATION

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The contours were drawn at every half‐foot. The elevation of the dam is 170 feet; thus, the

areas from elevations of 170 ft to 180.5 ft were considered. However, these areas did not

represent the actual flood‐stage areas, because west of the dam, there are several islands that

need to be included in the area calculations. If the water elevation was below the highest

elevation of the islands, then the areas of the islands were subtracted from the contour areas.

These flood‐stage areas were used in the HEC‐HMS model of the watershed’s reservoir. The

final flood‐stage‐area relationship can be found in Appendix E.

After preliminary runs of the HEC‐HMS model, we found that it was necessary to delineate

additional higher flood‐stage areas due to the water level rising higher than initially expected.

Using the contours shape file from the LVPC GIS database, contours and flood‐stage areas at

185 ft, 190 ft, 195 ft, and 200 ft were added.

3.3.2 Dam Discharge Modeling

An elevation‐discharge table was needed as the second input to HEC‐HMS reservoir model.

Historically the dam had a raceway on the north side that is about 5 feet above the top of the

dam. Today this raceway is filled in with concrete. Whenever the creek floods, water flows over

the raceway and the slope further up the bank of the creek, which is covered in rip‐rap. The

picture previously shown in Figure 3 was taken while standing on the raceway during baseflow

conditions. Figure 4 shows water flowing over the raceway. In extreme floods, water may flow

over the paved areas in the floodplain as well. A table showing the height of water over the

dam (h) vs. flow over the dam (Q) was needed to properly model how water would exit the

reservoir. As shown in Figure 9, the cross section of the dam was split into 4 sections:

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FIGURE 9 – 3RD STREET DAM CROSS SECTION

Section 2, which is the dam itself, was treated as a weir using the equation,

2/3w wQ C hL

Where:

Weir coefficient (Cw) = 4

h = height of water above the dam

Length of the weir (Lw) = 52 feet

The other sections were treated as open channels, so flow was determined using Manning’s

equation:

2/3 1/21.49hQ AR S

n

Where

n = manning coefficient of roughness (weighted by percent wetted perimeter of a

certain material)

A = cross sectional area of flow (ft2)

R = A/P (hydraulic radius where P = wetted perimeter)

S = slope (A value of 0.00365 ft/ft was used, which is the average slope of the lowest

reach of creek)

The flow from each section was summed to get the full flow for each elevation. The

spreadsheets used to make these calculations can be found in Appendix F.

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4. Results and Limitations

4.1 Results

Table 1 summarizes the results from the HEC‐HMS model, while Appendix G includes

hydrographs for the 2, 10, 25, 50, and 100‐year storms with storage plots for each storm, along

with an example of a raw output from HEC‐HMS.

TABLE 1 – HEC‐HMS MODEL PEAK FLOW RESULTS

*Level pond routing assumptions built into HEC‐HMS routing model are violated at highest flows due to negligible detention

storage

Our results show very little change in peak flows with removal of the dam. This leads to the

conclusion that the dam does not provide enough storage to have a significant effect on the

flooding. This finding is supported by the estimated storage volume calculation in Technical

Release 55, Urban Hydrology for Small Watersheds. According to NRCS TR‐55, the ratio of

outflow to inflow of a detention basin (qo/qi) is related to the ratio of storage volume to total

runoff volume (Vs/Vr) by the relationship shown in Figure 10.

*

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FIGURE 10 ‐ APPROXIMATE DETENTION BASIN ROUTING FOR RAINFALL TYPES I, IA, II AND III (NRCS, 1986)

The actual ratio of storage volume to total runoff for the 3rd Street Dam is 0.0010 for the 2‐year

return period. This ratio is so diminutive that it does not appear on the graph above. The

smallest storage volume to runoff volume ratio to appear on the graph is 0.18 (for Type II

storms as in the Lehigh Valley). Using the actual runoff volume generated by this watershed for

the 2‐year storm, the storage volume would have to be over 100 times higher (a value of 765

ac‐ft) to reach a value on the chart above. These calculations can be seen below for the 2‐year

design storm.

: VV

.18

: V 4250.6 ac ft

: V 765 ac ft

. . %

These calculations support the findings that dam removal will have no significant effect on the

peak discharge of the creek.

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4.2 Limitations

While our results show that the dam has negligible effect on the peak flows, some assumptions

had to be made during our work.

LVPC recently developed a HEC‐HMS model of the Bushkill Creek for 1990 land use data, which

yielded lower peak flow values than what was predicted by our model. The difference between

these values may be due to difference in CN values as the flows from our model are based on

higher adjusted CN values.

To determine the magnitude of this error, the HEC‐HMS model was adjusted to give the same

output as the LVPC 2‐year storm. This resulted in a ratio of storage volume to total runoff of

0.0017, which is higher than the ratio of 0.0010 determined by our model, but is still much too

low to result in a significant reduction in peak flows.

Some assumptions were necessary to calculate the different curve numbers for the land use

data. The curve numbers used were subjectively scaled to account for the provided GIS land

use layer, which was later discovered to be out‐of‐date. The amount of development and

impervious surface area within the watershed has changed significantly within the past twenty

years.

Channel widths, side slopes and depths were estimated based on aerial views provided by

Google Earth. The side slopes and depths were assumed to be consistent throughout the entire

creek. These estimates might have led to inaccurate K‐values. Also, the n‐values were based

on basic knowledge of the Bushkill Creek and may not reflect the actual conditions. The

properties of the other dams on the creek were assumed to be equal to those of the 3rd Street

Dam, because site‐specific data was not available.

The stage‐discharge table for the 3rd St. Dam may have had some inaccuracies in its modeling.

Exact dimensions, slopes and materials were not available without more extensive field work,

so some assumptions were made.

16

Never the less, none of these factors are likely to change the overall conclusions of the

modeling, that the 3rd St. Dam has a negligible impact on peak flows in the Bushkill Creek.

17

5. References

Free Printable Topo Maps ‐ Instant Access to Topographic Maps. Web. 10 Dec. 2010.

<http://www.digital‐topo‐maps.com/>.

LVPC (2009). “Lehigh and Northampton Counties Digital Geographic Data Disc.” (CD‐ROM),

LVPC, Allentown, PA.

Mays, Larry W. (2005). Water Resources Engineering, 1st Ed., Wiley, New Jersey

NRCS, (1986). “Technical Release 55.” Urban Hydrology for Small Watersheds, Washington

D.C.

The USGS Land Cover Institute (LCI). National Land Cover Dataset. 10 Dec. 2010.

<http://landcover.usgs.gov/>.

U.S. Geological Survey. Nazareth Quadrangle, Pennsylvania. 1:24,000. 7.5 Minute Series.

Washington D.C.: USGS, 1992.

U.S. Geological Survey. Easton Quadrangle, Pennsylvania. 1:24,000. 7.5 Minute Series.


USGS (2010). “Seamless Data Warehouse.” USGS, < http://seamless.usgs.gov/> (Oct. 27,

2010).

U.S. Geological Survey. Wind Gap Quadrangle, Pennsylvania. 1:24,000. 7.5 Minute Series.


US Army Corps of Engineers (ACOE) (2001). Hydrologic Modeling System HEC‐HMS, Version 2.1.

Galaxy Runtime Components by Visix Software, Inc.

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Appendix A – Curve Number Inputs

19

20

21

22

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Appendix B – Time of Concentration Data

TABLE B.1: TIME OF CONCENTRATION CALCULATIONS INPUTS

Little

Bushkill Zucksville Nazareth Belfast Forks Easton

Upper Main Stem

State Park

Length (ft) 57020 26162 41501 39509 26390 44765 49985 36243

Slope (deg) 1.64 0.75 0.78 1.41 1.14 1.33 1.38 1.37

Slope (%) 2.86 1.31 1.36 2.46 1.99 2.32 2.41 2.39

CN 76.19 69.69 71.13 76.81 70.31 71.23 74.31 72.78

S 3.125 4.349 4.059 3.019 4.223 4.039 3.457 3.740

Tc (hr) 5.35 5.09 6.94 4.23 4.09 5.63 5.54 4.49

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Appendix C – Baseflow Calculations

TABLE C.1: CREEK CHARACTERISTICS

Little Lehigh Creek Jordan Creek Monocacy Creek Bushkill Creek

Area (sq. mi) 80.8 75.8 44.5 79.1

% Forested 33 34 19 22.2

% Urban Area 11.0 3.7 12.0 14.2

% Carbonate 63.0 11.0 69.0 62.0

Weight 0.5 0.1 0.4 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

TABLE C.2: AREA‐SCALED BASEFLOW BY MONTH ‐ LOCAL USGS‐GAGED STREAMS (ALL FLOWS IN CFS)

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

Little Lehigh 111 121 138 146 119 105 90 78 79 76 81 104

Jordan‐scaled 156.5 62.6 219.1 176.3 120.0 90.8 58.4 57.4 73.0 77.2 116.8 163.8

Monocacy Scaled 106.6 117.3 135.1 133.3 103.1 94.2 80.0 72.9 76.4 76.4 83.5 104.8

Average 124.7 100.3 164.0 151.9 114.0 96.6 76.1 69.4 76.1 76.5 93.8 124.2

Weighted average 113.8 113.7 144.9 143.9 112.7 99.3 82.8 73.9 77.4 76.3 85.6 110.3

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FIGURE C‐1: BASEFLOWS BY MONTH

0

50

100

150

200

250

0 1 2 3 4 5 6 7 8 9 10 11 12

Baseflow (cfs)

Month

Monthly Baseflows

Little Lehigh Jordan‐scaled Monocacy Scaled Estimated Bushkill

26

Appendix D – K Calculations

TABLE D.1: MUSKINGUM K VALUE CALCULATIONS

Reach Length (ft) n Rh (ft) S V (ft/s) V (ft/hr) K (HR) n (sub‐reaches)

1 26296 0.04 3 0.005363553 5.695395 20503.42069 1.282518 2.565035406

2 13626.0 0.0 3.0 0.004669896 5.3 19131.7 0.7 1.4

3 3738.0 0.0 3.0 0.002942750 4.2 15187.2 0.2 0.5

4 6535.0 0.0 3.0 0.003825555 4.8 17316.0 0.4 0.8

5 4669.0 0.0 3.0 0.002998501 4.3 15330.4 0.3 0.6

6 9279.0 0.0 3.0 0.004634120 5.3 19058.3 0.5 1.0

7 2368.0 0.0 3.0 0.002956081 4.2 15221.5 0.2 0.3

TABLE D.2: REACH SLOPES

Belfast Forks Easton

Slope (%) 0.525 0.418 0.376

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Appendix E – Flood Stage Areas for 3rd St. Dam

TABLE F.1: FLOOD STAGE AREAS

Project: BushkillSimulation Run: 2 year new dam Reservoir: 3rd Street Dam

Start of Run: 21Nov2010, 00:00 Basin Model: Bushkill CreekEnd of Run: 24Nov2010, 00:00 Meteorologic Model: 2yrSCSCompute Time: 13Dec2010, 14:30:24 Control Specifications: 2yr

Volume Units: IN

Computed Results

Peak Inflow : 4113.0 (CFS) Date/Time of Peak Inflow : 21Nov2010, 20:30Peak Outflow : 4109.4 (CFS) Date/Time of Peak Outflow : 21Nov2010, 20:30Total Inflow : 1.00 (IN) Peak Storage : 4.4 (AC−FT)Total Outflow : 1.00 (IN) Peak Elevation : 6.1 (FT)

APPENDIX G: HEC-HMS RESULTS

Sto

rag

e (

AC

-FT

)

0.0

1.0

2.0

3.0

4.0

Ele

v (

FT

)

0.000.781.562.333.113.894.675.446.227.00

00:00 12:00 00:00 12:00 00:00 12:00 00:00

21Nov2010 22Nov2010 23Nov2010

Flo

w (

CF

S)

1,000

2,000

3,000

4,000

Reservoir "3rd Street Dam" Results for Run "2 year new dam"

Run:2 year new dam Element:3RD STREET DAM Result:Storage

Run:2 year new dam Element:3RD STREET DAM Result:Pool Elevation

Run:2 year new dam Element:3RD STREET DAM Result:Outflow

Run:2 year new dam Element:3RD STREET DAM Result:Combined Inflow

Sto

rag

e (

AC

-FT

)

2

4

6

8

10

12

14

Ele

v (

FT

)

1.71

3.43

5.14

6.86

8.57

10.29

12.00

00:00 12:00 00:00 12:00 00:00 12:00 00:00

21Nov2010 22Nov2010 23Nov2010

Flo

w (

CF

S)

0

2,000

4,000

6,000

8,000

10,000


Run:10 YEAR NEW DAM Element:3RD STREET DAM Result:Storage

Run:10 YEAR NEW DAM Element:3RD STREET DAM Result:Pool Elevation

Run:10 YEAR NEW DAM Element:3RD STREET DAM Result:Outflow

Run:10 YEAR NEW DAM Element:3RD STREET DAM Result:Combined Inflow

Sto

rag

e (

AC

-FT

)

0

4

8

12

16

Ele

v (

FT

)

0.001.563.114.676.227.789.3310.8912.4414.00

00:00 12:00 00:00 12:00 00:00 12:00 00:00

21Nov2010 22Nov2010 23Nov2010

Flo

w (

CF

S)

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000






Sto

rag

e (

AC

-FT

)

0

5

10

15

20

Ele

v (

FT

)

0.00

2.92

5.83

8.75

11.67

00:00 12:00 00:00 12:00 00:00 12:00 00:00

21Nov2010 22Nov2010 23Nov2010

Flo

w (

CF

S)

4,000

8,000

12,000

16,000






Sto

rage (

AC

-FT

)

0

5

10

15

20

25

30

35

Ele

v (

FT

)

0.00

2.29

4.57

6.86

9.14

11.43

13.71

16.00

00:00 12:00 00:00 12:00 00:00 12:00 00:00

21Nov2010 22Nov2010 23Nov2010

Flo

w (

CF

S)

0

5,000

10,000

15,000

20,000


Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Storage Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Pool Elevation

Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Outflow Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Combined Inflow

Documents

HEC HMS Modeling Report - Sites at LafayetteHEC‐HMS Runoff and Routing Model Stephen Beavan, Melanie DeFazio, David Gold, Peter Mara and Dan Moran CE 421: Hydrology Fall 2010 December