sign in sign up
<<
Home , Runoff curve number

Submitted via Facsimile

To: Ed Hanlon From: Martin L. Sohraidt, Ph.D. USEPA Sr. Project Manager M Office: Solon, Ohio

Date: January 24,1994 Subject: Hydrologic and Transport Analysis Backup Information As requested during the January 11, 1994 meeting and discussed with you on Jamuuy 21, 1994, Woodward Clyde Consultants (WCC) is submitting the following excerpts from existing document* for your review. Attached are the following: 1. Section 4.0 - Hydrologic and Analysis This section is a portion of the SQDi Phase I Report, Revision 0, that was submitted in October, 1992 (Pages 4-1 through 4-13). Cross-sections from the study area are provided (Figures 4-2 through 4-15). Please note that this version includes modificaUuus tlmt were made to the SQDI Status Report submitted in March, 1992. A copy of the text from the SQDI Status Report will be included in the package submitted tonight. 1. Appendix A • SQDI FSP Addendum 1 * Sour Depth Analysis This information was submitted with the SQDI FSP Addendum 1 - Revision 3 and included with Attachment C that was submitted to USEPA prior to the December 17, 1993 meeting (Pages C-1A through C-3A). V. As discussed with you on January 21, 1993, WCC will submit copies of this information to USAGE Waterways Experiment Station. Hard copies will be forwarded via Federal Express overnight. If you have any questions, please do not hesitate to give me a call. cc: Steve Golyski - USAGE Ron Heath - USAGE Waterway* Experiment Station Laura Weyer - CH^M Hill Joe Hciiiibudi - de maxbnis, inc.

i '*. -' r\' \ \ /•-.*** WoodwanM^yde

r

SQDI PHASE I REPORT REVISION 0 WoodwanMtyde Consultants SQDI Repoit. Phase i

4,0 HYDROLOGIC AND SF.niMF.NT TRANSPORT ANALYSIS

4.1 INTRODUCTION

The objectives of the Hydrologic and Sediment Investigation were to:

• Identify 10- and 100-year for selection of Phase n sampling locations; • Identify areas of sedimentation for selection of sediment sampling -> locations for Phase II sampling; C * Characterize the water and sediment moving within the watershed; and • Estimate potential sediment migration out of the watershed between the time of sampling and remediation.

The Fields Brook watershed is located approximately three miles northeast of the City uf Ashmbula, Ohio. Primary land uses of the watershed consist of a mix of residential, agricultural, and industrial areas. The soils in the watershed have been classified by the United States Department of Agriculture (USDA), Soil Conservation Service (SCS) and range from well-drained gravelly soils to poorly drained silty and sandy soils. The average annual rainfall for the watershed is 363 ia per year. The monthly precipitation distribution is relatively uniform throughout the year with the minimum mean monthly /"" •, precipitation of 222 in. in February and the mnYinmin precipitation of 3.61 in. in May. The average daily temperature ranges from 27 degrees Fahrenheit in January, to 73 degrees Fahrenheit in July (U.S Department of Commerce 1968).

Stream information was collected at 6 locations within the watershed in November and December of 1989, and in January, February, March, May, August, and September of 1990. Average at the outlet of Fields Brook was estimated to be approximately 22 cfs based on the discharge information collected during the above months. The stream in general is recharging in the downstream direction. The stream is gaining discharge from the industrial outfalls or from groundwater into the stream. It is difficult to quantify the exact amount which can be attributed torn

4-1 r\FBK\SQDIMT\SQDll-».RPT Woodward-Clyde Con*uKantS SQDI Report * Phase I

each source from the available data. Based on the volume of industrial outfall discharges collected by Source Control Remedial Investigation during Phase 0 sampling, the baseflow attributed from the industrial outfalls ranges between 14 find 18 cfs. The discharges from the industrial outfalls tend to vary with respect to time, and discharge measurements from the various outfalls were not taken at the same time. The potentiometric map, prepared as part of the fields brook Source control Remedial Investigation, Phase 0 Report, indicates tbat the groundwater surface intersects the stream within the study area and indicates a discharge of groundwater to the stream for the time period the groundwater data were collected. It is likely that the water level in the upper , which would directly affect the amount of groundwater discharge to c the stream, will fluctuate seasonally. 42 HYDROLOGIC ANALYSIS

The U.S. Army Corps of Engineers (USAGE), Package (HEC-1) computer model was used to simulate the rainfall-runoff process for the Fields Rroofc watershed. Drainage area, runoff characteristics, arid rainfall amounts were input into the model to estimate peak runoff rates and volumes at various locations for the 10-year and l(X>-year frequency events, The peak discharge values estimated from the Fields Brook watershed and the major floodplains were input into the USACE, Water Surface Profiles (HEC-2) computer program. The HEC-1 and HEC-2 analyses were used to estimate the 10-year and 100-year flood elevations to aid in refining the extent of contamination and to assist in the design of the remediation facilities.

4.2.1 Watershed Characteristics

The Fields Brook watershed consists primarily of industrial facilities and medium density residential areas with open areas of natural grassland. Fields Brook is a tributary of the Ashtabula , which ultimately discharges to Lake Erie.

Overland slopes range from less than 0.3 percent to 4 percent Runoff is conveyed predominantly from the southeast to the norttiwest by several small and

4-2 10-13-92 I:\FBK\5QQIRrT\SQDIM.Rn1 Woodward-Clydo Consultants SQDI Report - Phase I

irrigation ditches which collect and convey runoff to Fields Brook. The watershed was divided into several sub-basins to account for tributary flow as showu in Figure 4-1.

The soil types, hydrologic condition, and vegetative cover of the different sub- basins were identified to evaluate infiltration characteristics* The SCS "Soil Survey of Ashtabula County, Ohio" was used to identify major soil types and hydrologic classifications of the watershed. Three major soil group association* were identified in the Fields Brook watershed:

« Elnora-Colonie-Kingsville association Hydrologic Soil Group B

• Otisvilie-Chenango association Hydrologic Soil Group A • Conneaut-Swamon-Claverack association Hydrologic Soil Group C

An SCS runoff curve number was estimated to quantify infiltration potentials for each sub-basin based on the soil type, land use, hydrologic condition, and vegetative cover determined. Estimated curve numbers range from 61 to 83 for the different sub-basins.

Land use and vegetative cover as well as sub-basin drainage areas were estimated from . , United States Geological Survey (USGS) 7.5 minute quadrangle maps. Tie USGS 7.5 minute quadrangle maps used in the analysis were: (1) Ashtabula North, Ohio 1960, photo-revised 1970, photo-inspected 1988, (2) Ashtabula South, Ohio, 1960, photo- revised 1970, (3) Gogcvfflc, Ohio, 1960, photo-revised 1979, and (4) North Kingsville, Ohio, 1960, photo-revised 1979.

Tune of concentration (T^) for each sub-basin was estimated using the Kiipich Method for flow, aud SCS methods for overland and shallow concentrated flow. The Tc is defined as the time for water to travel from the most hydraulically remote point to th« outlet of each sub-basin. Slope and length of flow paths are the parameters necessary to estimate time of concentration using both the Kirpich and the SCS methods. Slopes

4-3 l.\rBK\SQDIRrT\SOOll-*.WT Woodward-Clyd* Consultant* SQDI Report * Phase I

and lengths were estimated from USGS 7.5 minute quadrangle maps. The drainage

area, Curve Number (CN)( lag time (TJ and Tc estimated tor each sub-basin arc given below: Are* Tf Tc Basin l.D. fgg- mihff) CN fhrt,>

A 0.097 76 0.49 0.81 B 0.189 83 0.44 0.73 C 0.105 74 0.74 1.23 D 0.097 73 0.73 1.21 E 0.784 61 1.21 2.01 F 0-239 80 0.98 1.63 ~r G 0364 82 0.60 1.00 ( H 0.062 76 0.73 1.22 I 0.044 78 0.33 0.54 J 0.124 80 1.27 112 K 0303 72 1.43 2.38 L 0.091 80 0.95 1.58 M 0.835 69 1.23 2.03 N 2.673 64 1.44 2.40

Baseflow in Fields Brook was estimated from the stream discharge information collected in November and December of 1989, and in January, February, March, May, August, and Sepiember of 1990. Precipitation records were reviewed with respect to tlic sampling dates to determine if discharge resulted from runoff from a storm event. The Amount / of precipitation in the period five days prior to the sampling was used to screen for discharge from runoff. UK average baseflow estimated at several locations along Fields Brook is presented below:

Design Point/ Baseflow BarfnlD _

1 22 2 21 3 20 4 12 5 8 6 4

4-4 10-13-92 I:\MUC\SUUIRFr\SQDlMRFr Ktvttioo U Woodward£tydt Consultant* SQDI Report - Phase I

Discharge from the industrial outfalls was measured in August and October of 1990 as part of the Source Conuoi, Phase 0 investigations. Average total discharges ranged from 14 to 18 cfs based on the data collected.

422 Rainfall Depth and Distribution

Rainfall depths for the 10-year and 100-year, 24-hour duration storms were estimated from National Oceanic and Atmospheric Administration (NOAA) Technical Paper 40 (TP-40). TP-40 is used for design purposes and is required for State permits in the State of Ohio. The total rainfall depths were then distributed using the SCS Type II temporal rainfall distribution curve. The 10-year and lOOyear, 24-hour duration precipitation depths were estimated to be 3.5 in. and 4.75 in., respectively, for the Fields Brook watershed

Rainfall of 3.95 in. in 18 hours was recorded at the WCC trailer located at the RMI Sodium site on September 7, 1990. Intensity-duratinn-freqn«ncy curves were developed from NOAA Technical Paper 40 (TP-40) for Ashtabula, Ohio to estimate the frequency of this rainfall event. The rainfall event was estimated to have a of 35 years for the 18-hour storm based on intensity-duration-frequency curves developed from TP-40 data.

, 4.2J Estimated Peak Flow*

The baseflow described above has been added to the I1EC-1 model to estimate the peak flow. The estimated peak flows (Q10 and Q100 for 10-year and 100-year precipitation in cubic feet per second, respectively) estimated from the HEC-1 model for the watershed are given in the table below:

Design Point/ Q19 Q1M Basin ID 1 913 1789 2 846 1687 3 799 1605

4-5 HM3-92 I:\rBK\SQDIR>'i\bgi>ll-»JUT RevWon 0 Woodward-Clyde Consultants SQDI Report Phase i

Design Point/ Qu Basin ID (cf*\

4 634 1283 5 544 1130 C 33 64 E 73 175 F 94 155 I 31 52 6 496 1052 7 335 734 c 4J FLOODPLAIN DELINEATION Hydraulic modeling of the Fields Brook floodplain was estimated using the USAGE'S Water Surface Profiles computer program, HEC-2. Cross-section data, discharge data, roughness coefficients, and reach lengths were input into the model to estimate flood depths and floodplain widths for both the 10-year and 100-year frequency events.

4,3,1 Approach

The floodplain cross-sections used in the HEC-2 model were taken from the stream sediment sampling program and the 1-ft aerial contour maps dated April 1987 by Kucera International The in-channe! sections were surveyed during the Phase I sediment f - sampling program (Section 3.2). All cross-sections were surveyed assuming the right edge of (looking downstream) was zero elevation and zero offset The in-channci zero elevation and offset points were assigned an elevation by plotting the cross-sections on tfce aerial contour maps. The foil floodplain cross-sections were plotted from left to right looking downstream. Cross-sections within the study area arc shown in Figures 4-2 through 4-15,

Manning's roughness coefficients were estimated from photographs of the reaches and from the aerial contour maps. The Manning's roughness coefficient accounts for channel and overbank roughness, vegetation, channel bends, arid meandering. The roughness values selected ranged from 0.045 to 0.06.

4-6 10-13-93 I;\rBK\5QD1R5T\SQDIl-».Ri'l R«vi«ioa 0 Woodward-CJydt Consultants SQDi Report - Phase I

Hydraulic routing typically includes both floodplain cross-sections and hydraulic crossings such as bridges and culverts. The survey data for the hydraulic crossings have not been completed at this time. Therefore, only the cross-sections with no hydraulic crossings were used in the hydraulic routing, Hydraulic crossings usually create additional head losses within the study area. The floodplain sections and the hydraulic crossings will be surveyed during the Phase n sampling.

4J2 Preliminaiy 10-Year and 100-Year Floodplain Delineation

The estimated flood elevations, reported relative to mean sea level (MSL) (NGVD 1929), based on hydrologic and hydraulic routing, and widths foi both die 10-year and 100-year frequency events, plus baseflow, are listed in the table below and are shnwn In Figures 4-2 through 4-15:

10-Yr. 100-Yr. Cross -section Elev Width Elev Hldtb ID nu Htt iflU ifii 1OCS2 578J 35 580.7 42 2-1XS2 5815 120 584.9 139 9-XS4 608D 30 6083 37 2-2XS1 5908 38 592.4 69 >XS5 OOOJ « 601.6 185 10-ixsn 6102 29 610.8 41 4-XS3 608.0 135 VM2 158 11-1XSS 614.6 26 615.0 32 f 5-1XS3 613.3 264 6143 285 1Z-XS2 625J 270 6263 276 &-1XS1 625^ 109 62&2 182 S-2XS1 63U 106 6318 141 8-2XS3 633.7 163 6363 319 8-3XS2 6393 165 6402 172

The estimated 10* and 100-year floodplain maps with cross-section locations are shown in Figure 4-16. Computed water surface elevations are shown in Figure 4-17.

4-7 io-13-n I:\rBK\*JL)|Ki'i\SQDIl-4.RFr Revision 0 Woodward-Clyde Consultants SQOI Report - Phase I

4.3.3 Calibration of Preliminary Floodplain Delineation

The estimated 10-year and 100-year flcxxlplains were compared to an observed flood event. The observed event on September 7, 1990 of 3.95 in. within an 18-hour period, has been estimated to be approximately a 35-year event Based on the level of engineering completed to date, the HEC-1 and HEC-2 models appear to represent the watershed reasonably well. The estimated 100-year event is greater than the observed 35-year event except in Reach 3 and Reach 6 where, in some locations, the estimated 100-year event has under-predicted the flood elevation compared to the observed event. In some cases, the 10-year event has over-predicted the flood elevation compared to the r observed event The results are summarized La the following table. Estimated Observed Estimated Cross-section 10-Year Eter 35-Year* Elev 100-Year Elev ID (IH (11) fin 1-XS2 578.5 579.0 580.7 1-XS10 5813 580.0 583.4 2-1XS2 582.6 581.0 584.9 2-2XS1 5908 591.0 592.4 3-XS1 593.7 599.0 595.2 3-XS5 600.4 601.0 601.6 4-XS3 608.0 6082 609.2 5-1XS3 6133 612.5 6143 6-XS2 617.8 618.7 618.6 7-2XS1 624.6 625.0 625.S c 8-1XS1 625.5 625.5 626.2 8-1XS9 630.6 630.6 631.6 8-2XS1 631.6 631.0 632.8 8-2XS3 635.7 Not Estimated 636J 8-3XS2 6393 Not Estimated 640.2

* Based on observed flood elevations at select locations.

The addition of data for the upstream hydraulic crossings at the Penn Central railroad tracks would probably show reduced flow entering the study area and would generally reduce the flood estimate throughout the study area. The addition of the hydraulic

4-8 10-1342 l:\FBK\SQDIRFT\SQDIl-(.RFr fceviiiouO Woodward-Ctydt Contuftants SQDI Report - Phase I

crossing data for the study will probably create additional head losses and local ponding that will change tbe profile near the culvert crossings due to the limited capacity of the hydraulic crossings. This is evident at cross-sections 3-XS1 and 6-XS2 which are located immediately upstream of a restricting hydraulic crossing. There was approximately five feet of bead loss observed for the hydraulic crossing upstream of 6-XS2 during a field visit on August 4, 1992: The head loss may be attributed 10 blockage of tbe culvert or a partial collapse of the culvert This will be confirmed during tbe Phase n campling survey. In these locations, the observed 35-year flood elevations are greater than the estimated 100-year flood elevations. When the remaining surveying for the hydraulic crossings and fluodplains is completed, tbe HEC-i and HEC-2 models will be calibrated using the September 7, 1990 event.

4.4 SEDIMENT ANALYSIS

A measure of whether a stream will transport sediment primarily by ur is based on the ratio of the shear velocity of the reach to the fall velocity of the sediment For ratios less than 0*5, most of the sediment will be transported by bed load. For ratios between OJ to 2.0, the transport of sediment will be bed load and some suspended load. For ratios greater than 2.0, the mode of transport win be primarily suspended load (Laursen 1960). For all stream reaches within the study area, the ratios exceed 10 assuming a median sediment size of 0.10 mm. The median sediment size was obtained from gradation analyses performed during the Phase 1 £ sampling program. Therefore, the primary mode of sediment transport tor Fields Brook is generally by suspended load. A report published by the USGS on Fluvial Sediment in Ohio reports that, in general, less than 10 percent of the sediment transport is by bed load for in the State of Ohio. Specifically, a gauge on the Ashtabula River at Ashtabula records that less than 5 percent of the sediment is transported by bed load (USGS 1978).

The Bagnold equation was used to estimate the total sediment load which may be transported by tbe stream. This equation was chosen not to quantify the amount of sediment being transported by the stream but 10 estimate the relative ability of tbe reaches to transport sediment By comparing the ability of a reach to transport sediment

4-9 10.1342 L\n»K\SQDIRTT,9QDn-i.RfT Woodward-Clyde Consultant* SQDI Report * Phase I

to the ability of the upstream reach to transport a given amount of sediment, a relutiuiisliip bclwccu readier uf aggradaliuu (icdiuiciit accumulation) aud degradmiini (tediment ) can he teen. Tf the upstream reach has a greater ability to transport sediment, then would occur in the subject reach. If the ability to transport sediment is less in the upstream reach, then degradation will occur in the subject reach. However, aggradation and degradation can vary from reach to reach depending on the magnitude of the How. This analysis represents in general the aggradation/degradation process for the entire floodplain area for the subject reach; however, local scour or may occur.

The Bagnold equation is based on the following factors:

\v. -v*) \***

where: QT * Total sediment discharge per unit time per ft width (tons/day/ft) 3 Yw « Specific weight of water (62.4 Ib/ft ) Yt " Specific weight of solids (168 Ib/ft3) 2 TO » Average shear stress on channel boundary (.16-3.57 Ib/ft ) U « Average flow velocity (2^-9.0 ft/sec) / e> » Efficiency factor (.11-.15) V. • tan« * Dynamic solid friction (.45-.90) W « FaJl velocity (.0002-147 ft/sec)

For comparison purposes, the 10-year event was selected for this analysis because of the higher probability of occurrence compared to the 100-year event The peak flow velocity estimates from the HEC-1 and HEC-2 analyses were used as input into the Bagnold equation. The duration of the peak flow was assumed to be constant for 1 hour. The results are shown in the following table.

4*10 10-13-92 i:\rBK\SQDlkPt\XtUU-4.Krr KevisioB 0 Woodward-Clyde Consultant* syui Report. Phase I

Estimated Total Sediment Load (tons/10-year peak flow) Aggrading/ RfiMTh ?*> Total Degrading 8-3 14 8-2 90 Degrading 8-1 880 Degrading 5,6,7 155 Aggrading 4 805 Degrading /' 3 180 Aggrading 2-2 920 Degrading 2-1 70 Aggrading 1 270 Degrading

The aggrading versus degrading conclusions are in general concurrence with the Geld observations with the exception of Reaches 8-1 and 8-2 (swampy area). Field observations confirm that large portions of degrading reaches are characterized by flow over coarser or relatively hard channel bottom (bedrock or hard clay layers of lacustrine sediments exposed by erosion).

C The sediment discharge from a watershed may he limited by the amount of available sediment to transport or by the ability of Fields Brook to transport sediment In general, the stream has the ability to transport sediment but is limited by the available sediment to transport.

One equation used to estimate the amount of overland erosion is the Universal SoQ Loss Equation (USLE). The USLE only accounts for overland erosion and does not account for other sources of sediment such as suspended sediment from outfalls, stream channel erosion, and stream bonk erosion. Estimating the amount of erosion from industrial outfalls, the stream channel, and bank erosion is difficult. To account for some of the major outfalls, suspended sediment data collected under the National Pollutant

4-11 10-13-92 I:\FBK\SQDIRPT£QDU-4.RFT Woodward-Clyde Consultants SQDI Report -

Discharge Elimination System (NPDES) program for the industrial outfalls will be collected during the Phase II sampling program and added to the total sediment load estimated from the watershed.

The USLE equation accounts for several factors:

A-RxKxLSxCTP

A - soil loss tons per year per acre R = rainfall factor (125) K » soQ erodibility factor (.120-.280) ^~ LS » length-slope factor (.148-1.468) ( C « crop management factor (.01) P • practice factor (1.0)

Annual soil loss for the Fields Brook watershed was estimated by the basins defined in the hydrologic investigation section. The rainfall factor, the crop management factor, and the erosiou control practice factor remained constant fur all ba»inv The length- slope factor and the soil erodihility factor varied depending on the characteristics of the basin. The crop management factor was selected based on a well-established watershed and was estimated as if the watershed was considered a meadow or grassland with 95 percent coverage. Values may range from 0.003 to 0.11. The Fields Brook watershed is a well-established watershed with no large-scale agricultural areas. The average soil / loss from the Fields Brook watershed was estimated to be 170 tons per year based on the USLE* For the Phase II report, existing suspended sediment data from the industrial outfalls will be collected and added to the USLE estimate. The estimated 170 tons per year converts to a discharge of sediment from the watershed of 130 cubic yards (assuming the sediment weight is 100 pounds per cubic foot).

The Bagnold equation is an example of one empirical total sediment load equatioa The Bagnold equation can account fur many sources of erosion but often produces erratic results without sediment load data to calibrate the equation. The Bagnold equation seems to produce unrealistic high concentration results and larger-than-expected sediment transport for this case without calibration data.

4-12 10*13-92 t:\FBK\5QDIRrT\5QDU-4.Ki'i Revision 0 Woodward-Ctycfc Consultants SQDI Report - Phas« I

The best estimate to date of the sediment discharge from the Fields Brook watershed is based on the USLE. No estimate of the sediment discharge from the industrial storm water outlets and stream bank and channel erosion was made for this sediment discharge estimate. The addition of hydraulic crossing data may affect the sediment load estimate. During Phase II sampling, suspended and bed load will be measured to calibrate an equation to estimate sediment discharge from the watershed.

c

4*13 10-13-92 IArOK\SQDlRn\SQDJl-4.RPT • Rcvkhjii 0 Ml-

4-2 WC9MK CROSS-MCMON 1-XS/ SIA. 2»45

(Mi RE1I>S BROOK rLOOOPUVN ^ M 3£ 2

C Woodward-Clyde Consultants -

013-

LJ Ld z en- Q I

6Q9-

100-YR FLOOD IO-YR FLOOD

I I I ~ -75 -50 -25 0 50 DISTANCE FROM CENTERUNE

FIG. 4-4 Job No. ; 66C3604?: CROSS-SECTION 9-XS4 STA. 3+00 Pr«pcr«

Out* . FIELDS BROOK FIOODPLA'.N B 6*^ d

-SO FK3L4 5 CROSS-SECTION 2-2XSI S7A. 45+50 ntxos DW INC..

(/•in»

*n<

VI u

C

c

- NOBVATIl MfldOOOU J8 SQTI3U Wcc/ki

OS+fr VIS NOUDK-SSOMD

«1 001 t j » a

! I v'irtj ai/j O -? & N u

I! _sS o

fPOU CPOtR.MC FK3. 4-9 CPOSS-SECnON 11-1XS5 STA 5 + 30

B*ta : U/»/»1 ntLDS Bfr »»->« FVOOO

no. 4-10 CROSS-StCIION S-IXS3 STA. 62+80 nnooic so FMM crmULMT

Ftt. 4-11

MA MCMMT CW)SS-SCCTIOH !2-)lS2 STA. 2+80

FIELDS OP* US-I

LJ

-ira

FK3 4-12 MCMOH CROSS -SECTION B-ISS STA. 111+60 noes BROOK rutocvun 636 H

634 H

$32 H

|630

I UJ

623 H

I -300 -200 -100 100 200 DISTANCE

FVO. «-1*| Job No. ; CROSS-SECTION 8-2XS1 STA. 125+80 by : J.H.S.

Octe : J/16/91 FIELDS BROOK FLOODPLAIN Woodward-Clyde Conoultanta »-

-8

-8

-O

tr. f U) ui U 8 •I

c

• 8•* I

r —r~ -1r 01 o to

4-14

Job No. : CROSS-SECTION 8-2XS3 STA. 138 + 30 Prcporvd by : J.H.S. S to »*) Dott : 1/16/91 FIELDS BROOK FLOOOPLAIN O Woodward-Clyde Consultants ~

-R

-8

UJ 2

UJ *. oLu

u. UJ

- O

CLCVATiON -

FIG. 4-15 Job N'o. : 86C3609E CROSS-SECTION 8-J.X52 STA. 161+60 Fr«porcd by : J.H.S.

Uote : 12/30/91 FIELDS BROO< FLOODPlAtN WbodwewLCIyde

C

SODI FSP ADDENDUM 1 REVISION 3

C Attachment C - Appendix A Fields Brook Sediment Operable Unit - SQDI FSP Addendum I 86C3609L

A.I Scour Depth Estimate lor Ftoldt Brook Channel In order to identify reaches of Fields Brook that are candidates for scour evaluation, an erosion model was used. The depth of scour during the 100-year flow event was estimated using the tractive force approach. This method involves an iterative procedure which was solved utilizing a programmable calculator. The method is based primarily on the sediment size found in the stream and the shear forces acting on the during the 100-year flow. The initial water deptii, dupe of the bed, energy grade line, and Manning's n values were obtained from the HEC-2 modeling presented in the Phase I SQDI Report (WCC 1992). Gradations of sediment, descriptions of sediment by reach and probing depths from the SQDF Phase I Report were reviewed as pan of this analysis. Results of this simplified method were compared to results obtained from a mass balance approach which Included erosion from the watershed and sediment transport of the various reaches. Aggradation or degradation (scour) was estimated from the ability of certain C readies to transport sediment The source of sediment includes the bed and that which is scoured from the channel bottom, A further comparison was made by increasing the channel cross-sections in the HEC-2 analysis by the depth of scour d&iu;iaicd in the tractive force method to simulate scour during the 100-year event. A.1.1 Assumptions

The depth of sediment in the stream bed were estimated from available data. Gradations of sediment were available only for the upper 6 in, of bed material (one gradation from a composite of sediment from 1 to 2 ft in depth was available in Reach 7). The size (diameter) of sediment at different depths was assumed A reasonable assumption is that the diameter of the sediment doubles for every 2 ft increase in depth. This is because the fact that the larger partide sizes ore not moved horizontally and thus, become a pan of the underlying sediment This process is called armoring and is expected to occur in the Fields C Brook channel Based on the gradations and stream characterizations available, some coarse gravel appears to exist in most of the readies.

The assumptions used in the analysis include: 1. Cohesion of the fine-grained particles is not considered This assumption implies that sediment is more likely to erode than if cohesion is considered.

2. The tke of sediment with 90 percent of material smaller than the given size (d*), based on the gradations, was used as the input sediment size for the first 2 ft of

3* Hie size of sediment corresponding to a coarse sand (5 nun) is used as the input sediment sfce for the sediment layer from 2 to 4 ft

C* 1 A Attachment C - Appendix A Fields Brook Sediment Operable Unit * SQDI FSP Addendum I 86C3609L

4. The size of sediment corresponding to a coarse gravel (20 mm) is used as the input sediment size for the sediment layer from 4 to 10 ft

5. Local scour around piers, abutments, etc., and contraction scour estimates are not included. The depth of scour may be greater near bridges and other hydraulic structures. 6. This analysis assumes "dear water scour and does not account for sediment being transported downstream. As such, results should be conservative since water transporting fine sediments is less likely to erode the channel* 7. Estimates of scour depth are based on limited hydrologic, hydraulic and sediment transport data analysis performed as part of the Phase I SQDL More detailed hydrologic, hydraulic and udiment transport analyses will be prepared as pan of the Phase n investigation. 8. Scoured areas, predicted during storm events, are refilled and restored by sedimentation occurring after the storm event so the original grade is maintained. A.12 Results Results of the analysis indicate that the size of sediment to required against the 100- year flood event is approximately 5 to 20 mm. The maximum scour depths computed for a 100-year flood event, based on the assumptions made for the sediment layers, were estimated to be from 2 to 5 ft This estimate should be reliable if 5 percent of the material in the sediment between 2 and 5-ft deep is 5 to 20 uiui ur greater (coarse sand to coarse gravel). From information in the Phase I SQDI Report, coarse material or bedrock is present in all of the reaches except Reach 5-2 and Reach 8-2. It is expected, however, that coarser sediment would be found in these reaches with increased depth. If significant amounts of sediment larger than 20 mm exist, or bedrock exists between 0 to 5-ft deep, the soour depth would be less than that predicted in this analysis. Fium the probe depths and reach characterizations obtained from the Phase I Report, bedrock is present in the reaches of Melds Brook west of Highway It thus limiting scour in these reaches. A.L3 Gwclosioaft Armoring of the channel during the 100-year flood event is expected to occur between 2 and 5 ft, based on the assumption that 5 percent of the sediment material has a grain size of 20 mm or greater. In Reach 1 through Reach 3, the scour potential is the greatest; however, bedrock is exposed at the channel base in these reaches. In the central reaches, coarse gravel and sands exist in the upper sediment layers. Coarse sands and gravels are assumed to exist in lower sediment layers in the upper reaches, although the 0 to 6 in. gradations do not indicate the presence of coarse materials.

C-2A Attachment C - Appendix A Fields Brook Sediment Operable Unit - SQDI FSP Addendum 1 86C3609L

The scour potential has been estimated in two ways:

1. Estimations of clear water scour potential using the tractive force approach. This is a conservative approximation based on the assumptions listed above. 2. Estimations of scour, based on a mass balance approach of aggradation and degradation, sediment transport potentials, and knowledge of existing stream bed conditions. The following scour depths are estimated based on the above analyses: 1. Reaches 1 through 3 may scour to bedrock, considering both methods o! estimating the scour potential. Average sediment thickness in Reaches 1 through 3 is not greater than 2.0 ft. 2. Reaches 4 through 5*2 may scour to 4 ft considering only clear water scour and may scour to 2 ft considering Method Number 2. 3. Reaches 6 and 7-1 may scour to 4 ft considering only clear water scour and may scour to 3 ft considering Method Number 2. 4. Reaches 7*2 and 8-1 may scour to 4 ft considering both methods of estimating scour potential.

3. Reaches 8*2 and 8-3 may scour to 3 ft considering both methods of estimating the scour potential o

C-3A