Pike_River_Ecosystem_Restoration_Project_Hydrology.pdf

Pike River Ecosystem Restoration Project

Phases 8 & 9

Village of Mount Pleasant, WI

HYDROLOGY

HYDRAULICS REPORT

January 2013

Pike River Ecosystem Restoration Project

Phases 8 & 9

Village of Mount Pleasant, WI

HYDROLOGY &

HYDRAULICS REPORT

January 2013

Pike River Ecosystem Restoration Project – Phases 8&9 4 Hydrology and Hydraulics Report

2.0 HYDROLOGIC ANALYSIS

To determine the hydrologic effects of the two alternatives on the Pike River and surrounding floodplain, both high and low discharge values were analyzed. Analyzing water levels of design flow events is necessary to determine the impact on the floodplain and any structures in the floodplain. Low flows must be analyzed to ensure adequate velocities during fish migration season and sufficient water levels for ecosystem functions.

2.1 Design Flow Events

Design flow events were analyzed to assess the effects of the design alternatives on the floodplain and any potential flooding impacts. The 100%, 50%, 20%, 10%, 2%, 1%, and 0.2% flow exceedance events were analyzed in this study. A hydrology model was provided by the local sponsor to the USACE Detroit

District, which estimated the design flow events using the Hydrologic Simulation Program – Fortran

(HSPF) software. For this study, these HSPF values were validated by comparing them to United States

Geological Survey (USGS) gage discharge values and Federal Emergency Management Agency’s

(FEMA) Flood Insurance Study (FIS) discharge values.

2.1.1 HSPF Discharge Values

HSPF is a comprehensive program intended to simulate watershed hydrology and water quality for both rural and urban environments. The current version of the model (11.0) was released by the United States

Environmental Protection Agency (EPA) in 1997. While there are a large variety of parameters that can be set within the model, the main inputs include rainfall time series, temperature and solar radiation, and land use patterns. HSPF produces a historic time series of discharge which includes baseflow and runoff.

Water quality parameters, sediment load, and detailed hydrographs are also predicted (EPA, 2012).

The base hydrologic model produced for this study was prepared by the Southeastern Wisconsin Regional

Planning Commission (SWRPC) in 1983 using HSPF. The model has undergone many revisions, the last of which was in 2009 by Crispell-Synder and Hey and Associates Inc. SEWRPC ran the model using the five following scenarios, altering land use and channel conditions:

Existing (1995) Land Use, Existing Channel Conditions

Planned Year (2020) Land Use, Existing Channel Conditions

Planned Year (2020) Land Use, Planned Channel Conditions in Mt. Pleasant

Planned Build-out Land Use, Existing Channel Conditions

Planned Build-out Land Use, Planned Channel Conditions in Mt. Pleasant

The Wisconsin Department of Natural Resources (WDNR) chose to continue analyzing alternatives based on the scenario: Planned Year (2020) Land Use, Planned Channel Conditions in Mt. Pleasant (Hey and

Associates, 2012). The results of the HSPF model are presented in Table 2-1. The modeled discharge locations listed in Table 2-1 are mapped in Figure 2-1. It is important to note that the Planned Year 2020

Land Use reflects flows based on Phases 1-9 of the Pike River Project as proposed design and construction, while the FIS flows that are published by FEMA May 2012 (and are discussed later in this report) represent flows based on Phases 1-3 as constructed and Phases 4-9 as existing.

Pike River Ecosystem Restoration Project – Phases 8&9 5

Figure 2-1 Modeled discharge locations from the HSPF model

Pike River Ecosystem Restoration Project – Phases 8&9 6

Table 2-1 Results from HSPF Model (cfs)

Location

Exceedance

Probability

Lamparek

Creek

Confluence

Chicory

Creek

Confluence

Waxdale

Creek

Confluence

Unnamed

Tributary

Confluence

1,150 ft

Downstream of Oakes Rd

Bartlett

Creek

Confluence

County

Highway C

0.2% 2180 2530 2530 1660 1450 1450 754

1% 1740 2050 2130 1360 1190 1150 599

2% 1560 1850 1960 1230 1080 1030 535

4% 1380 1660 1780 1110 967 910 472

10% 1140 1390 1540 937 821 751 389

20% 959 1190 1340 802 705 628 324

50% 689 876 1030 599 531 447 229

2.1.2 USGS Gage Data

The HSPF design flow events were compared to discharge values estimated using USGS streamflow data.

USGS Gage 04087257, Pike River near Racine, WI, is in closest proximity to the project and was used for this analysis (Figure 2-2). The gage is approximately 3.2 miles downstream of the project extent and has a drainage area of 38.5 square miles. Daily discharge values were collected at this site from October of 1971 to present (Figure 2-3).

Annual peak flow data are available at this gage (Figure 2-4) and were analyzed to determine flow values for given exceedance probabilities using the USGS program PeakFQ. PeakFQ estimates peak flows for specific recurrence intervals using the Pearson Type III frequency distribution to fit logarithms of instantaneous annual peak flows following Bulletin 17B guidelines from the Interagency Advisory

Committee on Water data (Flynn, 2006). The results were verified using the Weibull distribution and are presented in Table 2-2.

Pike River Ecosystem Restoration Project – Phases 8&9 7

Figure 2-2 Pike River USGS gage near Racine, WI

Figure 2-3 Daily discharge values for USGS gage 04087257

Pike River Ecosystem Restoration Project – Phases 8&9 8

Figure 2-4 Annual peak streamflow for the Pike River near Racine, WI

Table 2-2 Summary of flood frequency analysis for annaual peak flow at USGS gage 04087257

Probability (%) Discharge

0.2% 2400

1% 2100

2% 1950

10% 1560

20% 1350

50% 991

100%

As the Bulletin 17B method does not produce a 100% event, the 97.56% event was used in its stead.

2.1.3 Basin Adjustment Method Overview

In order to compare discharge values estimated from the gage data to the HSPF values, the gage data needed to be adjusted to represent the same drainage area. The basin reduction analysis was performed using the methods described in USGS Water-Resources Investigations Report on Flood-Frequency

Characteristics of Wisconsin Streams (2003). The report relates flood frequencies to drainage basin characteristics based on data collected at the 312 gaged sites in Wisconsin. Using a multiple-regression analysis, flood frequency characteristics can be estimated at rural and ungaged sites in Wisconsin for the

1%, 2%, 4%, 10%, 20%, and 50% flood events. Different methods are used for discharge estimations based on whether the site is gaged, near a gaging station, on a stream without a gaging station, or on a

Pike River Ecosystem Restoration Project – Phases 8&9 9 regulated stream. To improve accuracy, the state was divided into five area based on physiographic characteristics (Figure 2-5). The standard error prediction for the 100-year flood discharge ranges from

22% to 44% in the state.

Figure 2-5 Flood frequency areas in Wisconsin (Walker, 2003)

2.1.4 High Flows Basin Adjustment Application

The project is located on the border of Racine and Kenosha Counties; therefore, it is located within

Region 5 according to Figure 2-5. Since the site is near a streamflow gaging station, a combination of regression equations and the station’s flood frequency characteristics were used. Equation 2-1 presents the equation used for basin area adjustment.

Pike River Ecosystem Restoration Project – Phases 8&9 10

Equation 2-1 Procedure to estimate flood frequency characteristics on streams near gaging stations

The flood frequency characteristic value is determined by multiple-regression equations, which factor in the basin’s area, slope, and percentage of storage area. Different equations are used for each of the following events: 50%, 20%, 10%, 4%, 2%, and 1%, as shown in Figure 2-6. These equations are provided in Table 2 of the USGS report with “A” being the contributing area, “ST” storage in percent of basin area plus 1.0, and “S” being slope of the main channel (ft/mile).

Figure 2-6 Regression equations for Area 5 (Walker, 2003).

As there is no equation for the 100% and 0.2% annual exceedance probability events, the 50%, and 1% equations were substituted. Area and slope for the project location were measured in ArcMap based on

1/3-Arc Second National Elevation Dataset (NED).

Figure 2-7 differentiates the study drainage area and USGS gage drainage areas. Storage area was determined using drainage basin characteristic values provided in the USGS report appendix. No values were given for Pike River at gage 04087257; therefore, gage 04087250 in Kenosha, WI was used. The input values used for this analysis are presented in Table 2-3. The final adjusted values for the project location at the Chicory Creek Confluence (XS 12.47) in Figure 2-1 are presented in Table 2-4.

Pike River Ecosystem Restoration Project – Phases 8&9 11

Table 2-3 Input values for regression equations

Table 2-4 Summary of project area annual exceedance events

Probability (%)

Area Adjusted

Discharge (cfs)

0.2% 2320

1% 2030

2% 1880

10% 1470

20% 1260

50% 937

100%

Figure 2-7 Project and gage contributing drainage areas

2.1.5 FIS Discharge Values

Several flood studies have been conducted for the project area. The most recent flood study was performed in Racine County by Hey and Associates in 2012. The report provides the data and mapping necessary to remap the flood hazard area in the Village of Mount Pleasant, WI for the main stem of the

Gaged Site Parameters Project Site Parameters

Area sq. miles 38.5 17.6

Slope ft/miles 6.29 6.93

STorage % of basin area +1 1.97 1.97

Pike River Ecosystem Restoration Project – Phases 8&9 12

North Branch of the Pike River. This study was done to update the FIRM Panels 209D, 217D, 226D, 228D, and 236D of Map Number 55101C for the restored sections of the Pike River (Hey and Associates, 2012). The study was prepared under requirements of NR 116 of the Wisconsin Administrative Code. To complete floodplain mapping, relevant discharge values must be calculated. The discharge values calculated for the flood study are presented in Table 2-5.

Table 2-5 Summary of FIS discharge values from May 2012 FIS from FEMA (Hey and Associates, 2012)

Location

Lamparek

Creek

Confluence

Chicory

Creek

Confluence

Waxdale

Creek

Confluence

Unnamed

Tributary

Confluence

1,150 ft

Downstream of Oakes Road

Bartlett

Creek

Confluence

County

Highway

C

Cross Section 11.55 12.47 13.43 14.06 14.66 15.92 16.4

0.2% 2,340 2,410 2,270 1,470 1,390 1,440 753

1% 1,950 2,040 1,930 1,220 1,140 1,150 599

2% 1,790 1,870 1,790 1,110 1,030 1,030 535

4% 1,620 1,710 1,640 1,000 927 906 472

10% 1,390 1,490 1,440 858 785 749 388

20% 1,210 1,310 1,280 743 674 626 324

50% 921 1,020 1,020 567 505 446 229

2.1.6 Validation of HSPF Values

Figure 2-8 shows a comparison of the design event discharge values estimated from the HSPF model, at the USGS gage, and in the FIS study. Given the similarity of the values estimated, it was determined that the HSPF values are reasonable and were used for further analysis within this study.

Figure 2-8 Comparison of design flow events for different calculation methods

Pike River Ecosystem Restoration Project – Phases 8&9 13

2.2 Low Flow Discharge Events

2.2.1 Low Flow Discharge Calculation

Analysis of low flow discharge events is essential for ecosystem restoration projects, as sufficient water levels and velocities are required for a number of ecosystem functions including fish migration and spawning. The low flow events used for this study are monthly average flows for the period of March through June and monthly average flows of July and August. Real-time discharge (15-minute discharge readings) data from USGS gage 04087257 (Figure 2-2) were used to complete the low flow analysis. The

March through June low flow value was calculated by averaging the real-time discharge data during the months of March, April, May, and June for the entire period of record. The July low flow value was calculated by averaging all discharge values in the month of July over the entire period of record. The same method was used to calculate the August low flow value.

2.2.2 Low Flows Basin Adjustment Application

The low flow discharge values were adjusted using the same methods applied to the flood events. The lowest discharge event the regression equations account for is the 50% exceedance probability, so low flow discharges could not be calculated using this method. Alternatively, the adjustment ratio was calculated based on the 50% exceedance probability event using the top equation in Figure 2-6.

The same area, slope, and storage values were used for high flow discharge adjustments as were used for the low flow discharge adjustment. Once the adjustment ratio had been calculated, the seasonal low flow discharges were adjusted for the project site (Table 2-6).

Table 2-6 Low flow discharge values at USGS gage 04087257 and project site

Low Flow Event Gage Flows (cfs) Adjusted Flows at Project Site (cfs)

March - June 62.4 59.0

July 19.7 18.7

August 23.0 21.7