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HomeMy WebLinkAboutCT 14-10; POINSETTIA 61; SCOUR EVALUATION; 2017-12-18• TO: FROM: DATE: RE: TORY R. WALKER ENGINEERING RELIABLE SOLUTIONS IN WATER RESOURCES TECHNICAL MEMORANDUM Lennar California Coastal Attention: Jamison Nakaya 25 Enterprise, Suite 400 Aliso Viejo, CA 92656 Tory Walker, PE, CFM, LEED GA December 18, 2017 Scour Evaluation for Poinsettia Lane Bridge . . .. The proposed Poinsettia Lane Bridge spans an existing natural channel that runs south through the Poinsettia project site. The channel drains a limited area, which includes the natural area bounded approximately by El Camino Real, Cassia Road, and Poinsettia Lane, and a portion of the proposed Poinsettia residential development. As the channel will be subject to flood flows from storm events, and the bridge will be supported by piers along both sides of the channel, channel scour at the 100-year peak flow and the effect on the bridge foundations was investigated. This scour evaluation is in support of the bridge Foundation Report1, which will be used by others to confirm that the bridge pier footings have adequate embedment. SCOUR EVALUATION The hydrology at the proposed Poinsettia Lane Bridge is a key component of this scour evaluation. Based on the project's 100-year hydrology study2, the proposed condition drainage area and 100-year peak flow rate in the channel at the bridge location are approximately 36 acres and 49 cfs, respectively (this is the proposed condition drainage area and undetained 100-year peak flow at POC-3; copies of the hydrology maps are included in Attachment 1). It is clear, based on the hydrology maps, that the drainage area and peak flow are very small relative to the size of the channel and the bridge (35 feet estimated channel top width, flow depth of approximately 1-foot, and 110-feet approximate distance between bridge piers). Based on these observations alone, the risk of scour at the bridge is considered to be negligible. However, for the purpose of confirming what is physically and intuitively observed, a scour evaluation was completed using the allowable velocity method3• In the allowable velocity method, the average channel velocity obtained from a normal depth calculation is compared to the published allowable velocity for the channel boundary material (where allowable velocity is defined as the greatest mean velocity that will not cause the channel boundary to erode). Normal depth calculations were performed using the Hydraflow Express package by Autodesk. A representative cross section and channel slope (4.5%) were determined from the bridge plans and existing topography (as shown in the calculations and Channel Cross Section Map provided in Attachment 2). The Manning's n value of 0.06 was determined based on the extensive vegetation within the channel (observed during a site visit and in aerial imagery). This Manning's n value is conservative because following construction of the proposed development, the total volume of stormwater runoff to the WATERSHED, FLOODPLA IN ~ STORM WATER MANAGEMENT • RI VER RFSTORATION FLOOD FAClllTIES DESIGN · SEDIMENT 15-EROSION 122 CIVIC CENTER DRIVE, SUITE 206, VISTA CA 92084 · 760·414·9212 · TRWENGINEERING.COM -TRWE- Poinsettia Lane Bridge Scour Evaluation December 18, 2017 channel will increase, which will support the growth of even denser vegetation, resulting in a higher Manning's n than 0.06. The channel material and allowable ve locity were characterized from analysis of two sediment samples and the observed channel vegetation. Sediment gradations were developed for each sample indicating a mixture of silt and fine to medium grain sand, with a Unified Soil Classification of SM (silty sand). The sediment gradation results and boring information were obtained from the project's Foundation Report1 (see Attachment 3 for sediment gradation and boring info). Regarding channel vegetation, field observations show a dense mixture of shrubs, trees, and weeds on the channel bottom and banks. With the channel material and vegetation determined, Table 8-4 from the allowable velocity method guidance3 was used to select the allowable velocity for the channe l (Table 8-4 provided in Attachment 2). Based on the available options in Table 8-4, the channel corresponds best to "Grass-lined earth (slopes <5%), Bermuda grass, sandy si lt," which has an allowable ve locity of 6 ft/s. This selection is appropriate because the dense mix of shrubs, trees, and weeds have root systems that are stronger and more extensive than Bermudagrass. Figure 1 presents a typical view of vegetation in the channel, and Table 1 summarizes the results of the allowable velocity approach. . -. Figure 1. Typical vegetation in the Poinsettia channel, characterized by a dense mix of shrubs, trees, and weeds. TABLE 1. SUMMARY OF ALLOWABLE VELOCITY RESULTS 0 100 Flow Depth Velocity Channel Allowable Velocity (cfs) (ft) (ft/s) Material (ft/s) 49 0.89 3.1 Vegetation lined, 6.0 sandy silt 2 Job# 349-11 --TRWE Poinsettia Lane Bridge Scour Evaluation December 18, 2017 As shown in Table 1, the calculated design velocity in the channel is approximately 50% of the allowable velocity. Therefore, the channel will not erode and the potential for scour is considered to be negligible. This conclusion is further reinforced by the fact that allowable velocity values have a built-in factor of safety, meaning that they are somewhat less than the actual critical velocity required to move the channel boundary material. It should also be noted that the bridge piers are located outside of the 100-year water surface in the channel (the daylight elevation of the piers is approximately 1-foot or more above the 100- year water surface in the channel). Therefore, any potential local scour around the bridge piers is further reduced. CONCLUSION Based on TRW E's evaluation of the channel hydraulics and bridge plans, there is an extremely low risk of erosion in the channel for the 100-year event. The estimated channel scour depth as well as local scour depth around bridge piers is predicted to be negligible for the Poinsettia Lane Bridge. REFERENCES 1. Foundation Report Poinsettia Lone Bridges Carlsbad, California. December, 2017. Group Delta Consultants, Inc. 2. Technical Memorandum: Determination of Pre-and Post-Developed 100-year Peak Flow. August 9, 2017, Revised October 9, 2017. Tory R. Walker Engineering. 3. Chapter 8 Threshold Channel Design, National Engineering Handbook Part 654. August 2007. United States Department of Agriculture, Natural Resources Conservation Service. ATTACHMENTS 1. Hydrology Maps 2. Channel Cross Section Map, Normal Depth Calculation, and Allowable Velocity Table 3. Sediment Sample Gradation and Boring Information 3 Job# 349-11 ATTACHMENT 1 Hydrology Maps (From Reference 2) DEVELOPED CONDITIONS HYDROLOGY MAP POINSETIIA TORY R. WALKER ENGINEERING REL I ABLE SOLUTIONS IN WATER RESOURCES 122 CI VIC CENTER DR, STE 206, VISTA, CA 92084 · 760-414-9212 MAP SCALE 1" = 100' ~ I 0 50 100 2 00 OMA BOUNDARY INITIAL SUB -AREA FLOWLENGTH - BIOFILTRATION BASIN ---- ~ I CITY OF CARLSBAD 1111 ~ ~ BENCH MARK Description:------------------------------DE'vUOPED CONDITIONS HYDROLOGY MAP POINSEmA 61 Location:------------------------------- Record From: ____________________________ _ I · ~-Approved I Elev: Datum: _______________ _ ENGINEER OF WORK I ICheckod by Approvol dote ENGINEER RCE ''• .... 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WALKER ENGINEERING BENCH MARK Description:------------------------------ EXISTING CONDITIONS HYDROLOGY MAP POINSEmA 61 Location: ____________________________ _ 122 CIV IC CENTER DR, STE 206, VISTA, CA 92084 · 760 -414 -9212 Record From: ____________________________ _ Elev; Datum: ______________ _ I Approved I RELIABLE SOLUTIONS IN WATER RESOURCES ENGINEER OF WORK Checked by Approvol dote ENGINEER RCE ,, ATIACHMENT2 Channel Cross Section Map, Normal Depth Calculation, and Allowable Velocity Table ND . t· n (feet) LEGE · t· 9 eleva 10 \ b ttom of foo in Indicates 0 ( z / ,c, coo,trucUoo / ~ \'> ~ lodicates "'" I RIPARIAN z ,c> .;1 g N 11 ;i., shawo) I 1:1 ~ ) YJ HABITAT/~\~ :g /2.,\: a ,,,;cotes CIDH pa, (oat a p I • • § ~I N O ~ d 1 w / \ N l, --o ( Oi cj I vi ~ ' X E . t fence to be remove ' ~ io O -'\ ,J I -X--XIS , / >-I \ . * /,. / / < ~ , ~ I y I (USE / :-_ I \... \ \\ -EC t95+ 78.21 CHANNELFLOW LINE . °N ! 190.00 • I ) \ ~-I I I ~ I I --I I I I "" L~. I ----l ~ \ I J ii I -----/ ~, _/ l I . I ·' /(: I . I /, -/IA ~ -'K ,,/'_/ s3s·11·21 '' • I ,,_o+oo **'" ~ I 1, ·I 6 l{) 0 l{) r N ~ 0 N N . / ) ,i I , , j 189+11.50 ' b I . / . ~/'~ ' ( 1 ,ss.00 I . '\ '•s\ g . { U"l 0 N ~ CHANNEL CROSS SECTION AND BRIDGE LAYOUT MAP POINSETTIA LANE BRIDGE vllCII II lt::I nt::tJUI L Hydraflow Express Extension for Autodesk® AutoCAD® Civil 30® by Autodesk, Inc. Poinsettia Bridge Channel User-defined Invert Elev (ft) Slope(%) N-Value Calculations Compute by: Known Q (cfs) = 194.20 = 4.50 = 0.060 Known Q = 49.00 Highlighted Depth (ft) Q (cfs) Area (sqft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Ye (ft) Top Width (ft) EGL (ft) Tuesday, Dec 12 201 7 = 0.89 = 49.00 = 15.79 = 3.10 = 34.43 = 0.82 = 34.37 = 1.04 (Sta, El, n)-(Sta, El, n) ... ( 0.00, 203.00)-(4.30, 202.00, 0.060)-(8.60, 201 .00, 0.060)-(13.40, 200.00, 0.060)-(1 8.40, 199.00, 0.060)-(24.40, 198.00, 0.060)-(35.00, 197.00, 0.060) -(48.50, 196.00, 0.060)-(67.80, 195.00, 0.060)-(91 .50, 194.20, 0.060)-(99.80, 195.00, 0.060)-(106.80, 196.00, 0.060)-(113.90, 197.00, 0.060)-(121.90, 198.00, O.i -(134.10, 199.00, 0.060)-(146.80, 200.00, 0.060)-(160.80, 201 .00, 0.060) Elev (ft) Section Depth (ft) 204.00 9.80 202.00 200.00 198.00 196.00 \ \ / \ / V \ ~ ., ~ I "' '-~ I 7.80 5.80 3.80 1.80 194.00 ~ ~ -0.20 192.00 -2.20 -20 0 20 40 60 80 100 120 140 160 180 200 Sta (ft) Chapt.er 8 Threshold Channel Design Part654 National Engineering Handbook Table 8-4 Allowable velocities Channel mat.erial Mean channel velocity (ft/s) (mis) Fine sand 2.0 0.61 Coarse sand 4.0 1.22 Fine gravel 6.0 1.83 Earth Sandy silt 2.0 0.61 Silt clay 3.5 1.07 Clay 6.0 1.83 Grass-lined earth (slopes <5%) Bermudagrass Sandy silt ~ 6.0 1.83 Silt clay 8.0 2.44 Kentucky bluegrass Sandy silt 5.0 1.52 Silt clay 7.0 2.13 Poor rock (usually sedimentary) 10.0 3.05 Soft sandstone 8.0 2.44 Soft shale 3.5 1.07 Good rock (usually igneous or hard metamorphic) 20.0 6.08 (210-VI-NEH, August2007) 8-7 ATIACHMENT 3 Sediment Sample Gradation and Boring Information 100 90 80 -.r::. .Q> 70 Cl) 3: ~ 60 ~ Cl) C: U:: 50 c Cl) ~ 40 Cl) Cl. 30 20 10 0 100 3" 11/." COARSE GRAVEL SAMPLE "14" BORING NUMBER: A-17--002 SAMPLE DEPTH: O' -3' 3/8" +-0% Gravel 10 FINE U.S. Standard Sieve Sizes #4 #A ,111~ # ,n ,11;n #100 #200 I -......, I I 97 I '\. I I I \ ~ ' 'C .... \~ . \ \ \ \ -, ..., I I I ! 11 I I I I I 51% Sand+-+ , 49% Fines-I '' ' ' I 1 0.1 Grain Size in Millimeters COARSE MEDIUM FINE SAND UNIFIED SOIL CLASSIFICATION: SM DESCRIPTION: SIL TY SAND L:iti(CUP DELTA SOIL CLASSIFICATION 0.01 SILT AND CLAY 0.001 A TTERBERG LIMITS LIQUID LIMIT: - PLASTIC LIMIT: - PLASTICITY INDEX: - Document No. 17-0065 Project No. SD412A FIGURE B-1.5 100 90 80 .., .c -~ 70 Q) ~ ~ 60 .... Q) C: U:: 50 .., C: Q) ~ 40 Q) Cl. 30 20 10 0 100 3" 1Y." COARSE GRAVEL SAMPLE < /4" BORING NUMBER: A-17-003 SAMPLE DEPTH: O' • 5' 3/E" +-0% Gravel 10 FINE U.S. Standard Sieve Sizes #4 #8 ~A~· # .n #50 #1no #2fn I -I " I I \ ::R I I I \ I I \ I I \ I I I I I \ I ; \ ~ I I I \ I I ~ :::,q I I I \ I ' \ I " ' \ ~ ~,. ,a I I I I I I I I 74% Sand -I 26% Fines-+ ' I I 0.1 Grain Size in Millimeters COARSE MEDIUM FINE SAND UNIFIED SOIL CLASSIFICATION: SM DESCRIPTION: SIL TY SAND l..:iliii(CUP DELTA SOIL CLASSIFICATION 0.01 SILT AND CLAY 0.001 A TIERBERG LIMITS LIQUID LIMIT: - PLASTIC LIMIT: - PLASTICITY INDEX: - Document No. 17-0065 Project No. SD412A FIGURE B-1.10 EXPLANATION: A-17-004~ Approximate location of exploratory boring (TD-Total Depth). 8 Approximate location of R-Value sample for pavement design. N A NO SCALE GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO. CA 92126 (858) 53&-1000 PRoJECT- Poinsettia Lane Bridges Lennar Homes PRoJECT NlMBER SD412A DClCtMHT NlMBER 17-0065 AGU<ENUIIIIER 18 SITE VICINITY PLAN I' \ / / \ / / / / \ " DENSE BRUSH GNV REFERENCE: O'Day Consultants (2017). ' ' ~ " ......... '-.. - I l> I . I ( ' ~4{ \ \ I \ \ 'x' /\\ \/\ 1418 Bridge Boring Coordinate Exhibit, June 2. ;· .......... / X '- 205.6 X -- - ~ EXPLANATION: A-17-004~ Approximate location of exploratory boring (TD-Total Depth). N A NO SCALE ~ GRCI..JP OFl :TA GROUP DELTA CONSULTANTS, .. c. ENGINEERS ANO GEOLOGISTS 9245AC1M1YROAD, SUITE 103 SAN DIEGO, CA 92126 (858) 536-1000 PROJECT- Poinsettia Lane Bridges Lennar Homes PROJECT NlMIER SD412A OOClAIEHT NIAIBER 17-0065 FIGURENIJMIER 3A EXPLORATION PLAN I I I I I I WEST ":..."":..-----:,,...r:.:.;:. ......... ___ _ 220' ELEV. 212 ft. 200' ... ········-·· ............ _.,, 180' 160' ~ 140' u.. -~ I ~, 120· z 0 I ~100· UJ ...J w 80' 60' EXPLANATION: BORING LOG ELEV.21211.1·. SM' Surface / :· , Elevation 16 .... · : sc Soil Profile with I / · .':' uses Soil Type' N60Bow 15 . CL-/-Counts , &1,<r> ~ Groundwater Level Tota10epth,10tt. -Total Depth Drilled 1: Refer to Legend In Appendix A. IJ1 t "" ~p ~ >.~ ~ . ,L I.. ----- ··················· ......................... . 133 192 CL SM TSA 102 170 110 CH TSA SM 137 CL SM CL SC CL SM CL SM 200 Total Depth: 120ft. GEOLOGIC INFORMATION PROPOSED ALIGNMENT Queried Geologic where Contact , QAL I uncertain ................................. , ............. ,,,?,--.. , ..... ;ii ... .. T / SA Alluvium Santiago Formation Alignment \ A-17-001 .--Boring ID I I I~ 187+00 ---Location on "" alignment Stationing T EAST ~~~~---~-~rr-~~--------~--· ......... ~ .::, .............. ?,···------- "Ii,.,... r . ~ -----_ ---'"·;,"";;;::_ ---- FINISHE1 GR~r E ___ .,. Ill ~~\., n, :;::;:;i ML 110 CL 92 SM 127 138 ML ...................... 1 ...................................................... " "' ,. "' .. ... TSA ... "' ,,. " ,,. ,... , .. oc '-Of:UCl'.4L Cf.'0 ·NJ:, .. ,... ........ ? .............. ?A,LQtli, MC.HT EDCE er .:>E<.t Total Dtpth: 81ft. 138 ..... SM 110Wtj sc 200+· TOia! Depth: 110ft. ELEVATION Elevation above I Mean Seal Level (MSL) 200' 1" = 30' HORZ. 1" = 30' VERT. II ~II }," 1 GROUP CEL TA GROUP DELTA CONSULTANTS, INC~ ENGINEERS ANO GEOLOGISTS 9245ACTIV1TY ROAD, SUITE 103 SAN DIEGO, CA92126 (858) 536-1000 66X1Cr'ft.11t.Ui:i PROJECT NUMBER SD412A 17-0065 Poinsettia Lane Bridges Lennar Homes I 38 GEOLOGIC CROSS SECTION