Bushkill Creek 3 rd Street Dam Removal Analysis

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1 Bushkill Creek 3 rd 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

2 Contents 1. Objectives and Tasks Site Description Methods Sub basin Modeling NRCS Curve Numbers Time of Concentration Baseflow Reach Modeling Reservoir Modeling Results and Discussion Results Limitations References 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 3 rd St. Dam Appendix F Stage Discharge Table Spreadsheet Calculations Appendix G HEC HMS Results 1

3 1. Objectives and Tasks To determine the effect of removing the 3 rd Street Dam on peak flows in the Bushkill Creek, a model of the Bushkill Creek Watershed and the 3 rd 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 3 rd Street Dam, as well as the stagedischarge 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. 2

The surrounding area includes scattered woods, but primarily consists of paved streets and buildings.

4 FIGURE 1 BUSHKILL CREEK WATERSHED (DIGITAL TOPO MAPS) The 3 rd 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 3

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

) FIGURE 4 DAM UNDER STORMFLOW CONDITIONS (BRANDES, D.) 3.

5 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 3 rd 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. 4

6 3.1 Sub basin 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 subbasins. 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) 5

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.

7 FIGURE 6 HEC HMS REPRESENTATION OF THE BUSHKILL CREEK WATERSHED 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 6

8 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 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 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) 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). 7

9 The results of the time of concentration calculations can be found in Appendix B 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 8

10 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: Where: V = velocity n = Manning s n value R h = 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, R h, 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 Reservoir Modeling Stage Area Relationship The 3 rd 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 3 rd Street Dam, and since no stage storage and outflow data were available, the sizing data of 9

Survey Report, Nov 2010 ; contour lines from these points were created using AutoCAD Civil 3D to develop the

11 the 3 rd 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 10

12 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 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 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: 11

13 FIGURE 9 3 RD STREET DAM CROSS SECTION Section 2, which is the dam itself, was treated as a weir using the equation, Where: Weir coefficient (C w ) = 4 h = height of water above the dam Length of the weir (L w ) = 52 feet Q C hl w 2/3 w The other sections were treated as open channels, so flow was determined using Manning s equation: 1.49 Q AR S n 2/3 1/2 h Where n = manning coefficient of roughness (weighted by percent wetted perimeter of a certain material) A = cross sectional area of flow (ft 2 ) R = A/P (hydraulic radius where P = wetted perimeter) S = slope (A value of 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. 12

14 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 (q o /q i ) is related to the ratio of storage volume to total runoff volume (V s /V r ) by the relationship shown in Figure

15 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 3 rd Street Dam is 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. : V V.18 : V 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. 14

16 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 , which is higher than the ratio of 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 3 rd Street Dam, because site specific data was not available. The stage discharge table for the 3 rd 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. 15

17 Never the less, none of these factors are likely to change the overall conclusions of the modeling, that the 3 rd St. Dam has a negligible impact on peak flows in the Bushkill Creek. 16

18 5. References Free Printable Topo Maps Instant Access to Topographic Maps. Web. 10 Dec < 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, 1 st 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 < U.S. Geological Survey. Nazareth Quadrangle, Pennsylvania. 1:24, Minute Series. Washington D.C.: USGS, U.S. Geological Survey. Easton Quadrangle, Pennsylvania. 1:24, Minute Series. Washington D.C.: USGS, USGS (2010). Seamless Data Warehouse. USGS, < (Oct. 27, 2010). U.S. Geological Survey. Wind Gap Quadrangle, Pennsylvania. 1:24, Minute Series. Washington D.C.: USGS, US Army Corps of Engineers (ACOE) (2001). Hydrologic Modeling System HEC HMS, Version 2.1. Galaxy Runtime Components by Visix Software, Inc. 17

19 Appendix A Curve Number Inputs 18

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21 20

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24 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) Slope (deg) Slope (%) CN S T c (hr)

25 Appendix C Baseflow Calculations TABLE C.1: CREEK CHARACTERISTICS Little Lehigh Creek Jordan Creek Monocacy Creek Bushkill Creek Area (sq. mi) % Forested % Urban Area % Carbonate Weight 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 Jordan scaled Monocacy Scaled Average Weighted average

26 250 Monthly Baseflows 200 Baseflow (cfs) Month Little Lehigh Jordan scaled Monocacy Scaled Estimated Bushkill FIGURE C 1: BASEFLOWS BY MONTH 25

27 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) TABLE D.2: REACH SLOPES Belfast Forks Easton Slope (%)

28 Appendix E Flood Stage Areas for 3 rd St. Dam TABLE F.1: FLOOD STAGE AREAS 27

29 APPENDIX G: HEC-HMS RESULTS Project: Bushkill Simulation Run: 2 year new dam Reservoir: 3rd Street Dam Start of Run: 21Nov2010, 00:00 Basin Model: Bushkill Creek End of Run: 24Nov2010, 00:00 Meteorologic Model: 2yrSCS Compute Time: 13Dec2010, 14:30:24 Control Specifications: 2yr Volume Units: IN Computed Results Peak Inflow : (CFS) Date/Time of Peak Inflow : 21Nov2010, 20:30 Peak Outflow : (CFS) Date/Time of Peak Outflow : 21Nov2010, 20:30 Total Inflow : 1.00 (IN) Peak Storage : 4.4 (AC FT) Total Outflow : 1.00 (IN) Peak Elevation : 6.1 (FT)

30 Reservoir "3rd Street Dam" Results for Run "2 year new dam" Storage (AC-FT) Elev (FT) 4,000 3,000 Flow (CFS) 2,000 1,000 00:00 12:00 00:00 12:00 00:00 12:00 00:00 21Nov Nov Nov2010 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

31 Reservoir "3rd Street Dam" Results for Run "10 year new dam" Storage (AC-FT) Elev (FT) 10,000 8,000 Flow (CFS) 6,000 4,000 2, :00 12:00 00:00 12:00 00:00 12:00 00:00 21Nov Nov Nov2010 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

32 Storage (AC-FT) Flow (CFS) ,000 12,000 10,000 8,000 6,000 4,000 2,000 Reservoir "3rd Street Dam" Results for Run "25 year new dam" 0 00:00 12:00 00:00 12:00 00:00 12:00 00:00 21Nov Nov Nov Elev (FT) Run:25 YEAR NEW DAM Element:3RD STREET DAM Result:Storage Run:25 YEAR NEW DAM Element:3RD STREET DAM Result:Pool Elevation Run:25 YEAR NEW DAM Element:3RD STREET DAM Result:Outflow Run:25 YEAR NEW DAM Element:3RD STREET DAM Result:Combined Inflow

33 Reservoir "3rd Street Dam" Results for Run "50 year new dam" Storage (AC-FT) Elev (FT) ,000 12,000 Flow (CFS) 8,000 4,000 00:00 12:00 00:00 12:00 00:00 12:00 00:00 21Nov Nov Nov2010 Run:50 YEAR NEW DAM Element:3RD STREET DAM Result:Storage Run:50 YEAR NEW DAM Element:3RD STREET DAM Result:Pool Elevation Run:50 YEAR NEW DAM Element:3RD STREET DAM Result:Outflow Run:50 YEAR NEW DAM Element:3RD STREET DAM Result:Combined Inflow

34 35 30 Reservoir "3rd Street Dam" Results for Run "100 year new dam" Storage (AC-FT) Elev (FT) ,000 15,000 Flow (CFS) 10,000 5, :00 12:00 00:00 12:00 00:00 12:00 00:00 21Nov Nov Nov2010 Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Storage Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Outflow Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Pool Elevation Run:100 YEAR NEW DAM Element:3RD STREET DAM Result:Combined Inflow

Section 4: Model Development and Application

Section 4: Model Development and Application The hydrologic model for the Wissahickon Act 167 study was built using GIS layers of land use, hydrologic soil groups, terrain and orthophotography. Within