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HomeMy WebLinkAboutFDP201900004 Permit Floodplain Development Permit 2019-06-07 of aL.£14 r,r'PR I A OVED C.141—ti arfe County 19.160. �► ,e�te _ - .DePartm@11t lRcir .SIC COUNTY OF ALBEMARLE ZO -0000 Department of Community Development 401 McIntire Road Charlottesville,Virginia 229024596 Phone(434)296-5832 Fax(434)972-4126 FLOODPLAIN DEVELOPMENT PERMIT This form is intended to aid the Department in documenting and characterizing the nature of development proposed in the floodplain. Development includes buildings or other structures,mining,dredging,filling, grading,paving,excavation or drilling operations or storage of equipment or materials. The form responses will be used to determine whether a floodplain impact plan or special use permit is required. Please check one: ® New Submittal with no anticipated floodplain impact(no floodplain impact plan) ❑ New Submittal with an anticipated floodplain impact. Please include a floodplain impact plan. FEE required with submittal: $323 (Code 18-35.1 g) ❑ FEMA Letter of Map Change(LOMA,LOMR) Please include a complete copy of all material to be submitted to FEMA. Include any computer models (HEC-RASfiles)on a disc. FEE required with submittal: $161 (topographic info only),or$323(floodplain modeling) ❑ New Submittal with a Zoning Special Use Permit.Please include a floodplain impact plan. FEE required with submittal: $323 ❑ Resubmittal (Floodplain Development Permit Number ) Please include your response form from the original submittal. FEE as above required with each resubmittal. A Floodplain Impact Plan, Special Use Permit,or FEMA Map Change will need to follow Zoning Floodplain Overlay District requirements(County Code 18-30.3), found at http://www.albemarle.org/upload/images/Forms_Center/Departments/County_Attornev/Forms/Albemarle County Code Ch 18_Zoning30_Overla _Districts.pdf Section 4 of the Design Standards Manual provides a list of required items to be included in a Floodplain Impact Plan. This can be found at http://www.albemarle.org/department.asp?department=cdd&relpage=4447. Oakencroft Holdings, LLC Owner Name(Print) Home Phone Office/Other Phone 410 East Water Street#500 Address Charlottesville Virginia 22902 City State Zip Code Tax Map&Parcel Number 59-32&59-32A Project Name(if applicable) Oakencroft Farm �^ Building Permit or Project Number(if applicable) - t* LUX- 11/1/2015 Please describe the nature of the development activity proposed within the floodplain (e.g. new structure, grading for a playing field, driveway stream crossing, installation of a fence,etc.): The purpose of this floodplain development permit is to replace two existing deteriorated bridges. (Please attach any plans or photos to this application) 1. If a structure is proposed,is the structure accessory to a recreational or agricultural use? Yes❑✓ No ❑ N/A 2. Does the proposed activity involve a stream crossing for a pedestrian trail or driveway serving a single family dwelling? Yes❑No ✓❑ N/A 3. Does any proposed fencing cross a stream channel? Yes❑No ElN/A 4. If any fill is proposed,please appro 'mate the proposed amount of fill in the floodplain See Site Plan Owne • gent 'ignature ��� i/�/!,� ij Date 12 (FOR OFFICE USE ONLY) Checked By Date (for resubmittals) Fee Amount$ Date Paid By Who? Receipt# Check# • MAR 0 7 2O19 COMMUNITY D Lo»win,- 1I/1/2015 WOOLLEY ENGINEERING March 5, 2019 Frank Pohl, P.E. County of Albemarle 401 McIntire Road Charlottesville, Virginia 22902 Re: Oakencroft Farm: Bridge Replacement Floodplain Impact Documents Dear Mr. Pohl, This memorandum shall provide floodplain evaluation and design calculation results for the Oakencroft Farm bridge replacement project. As background, Oakencroft Farm is comprised by two parcels under the same ownership. The parcels are located at 1455 Oakencroft Circle and 1376 Oakencroft Lane. Two existing bridges on the properties span an unnamed tributary to Ivy Creek, and provide access for the agricultural use of the properties. Recent storm events have damaged both bridges. The shorter span bridge, labeled as"Bridge#1" on the accompanying plan,was completely washed away, leaving only the abutments currently in place. The support structures for"Bridge#2"have been undermined by scour and are currently unsafe for use. The current FEMA Flood Insurance Rate Map indicates that the project area is within a"Zone A"hazard area. Due to the undefined nature of"Zone A"overlay, the initial scope of our work was to evaluate the existing site-specific floodplain at the two crossings. The second focus of our work was to study how an improved replacement crossing at each location would impact the the base flood elevations. In each of the two locations,the property owner would like to replace the damaged bridge with an improved new structure. An engineering analysis has been conducted to refine the bridge span dimensions and deck elevations to enhance each crossing's ability to adequately pass the more frequent storm events while not adversely affecting the flood elevation of the 100-year frequency storm event. We relied on both County-provided GIS mapping and USGS mapping to determine the area that comprises the watershed boundary. A field-verified topographic survey was performed by Roger Ray and Associates, at a precision to generate one-foot contour intervals for the immediate project area. We utilized cross section data from the field-verified topographic survey and County mapping to model the creek using HEC RAS software. We determined the baseline flood elevations for the 100-year floods as 459.35 feet at bridge crossing#1 and 459.26 feet at bridge crossing#2. As we studied the in situ condition of Bridge crossing#1, it was evident that earthwork had occurred in the past to allow for a shorter bridge span. Our proposed new structure intends to remove the truncation of the stream channel at the crossing to more consistently match the WOOLLEY ENGINEERING 220 East High Street (434)973-0045 Charlottesville,Virginia 22902 110 WOOLLEY ENGINEERING upstream and downstream condition, and to raise the top of the proposed new bridge deck by one foot. This should provide ingress/egress in a more consistent manner, while also reducing the probability of clogging of the span. At bridge crossing#2,we have enhanced the existing bridge structure by removing two sets of piers that are in the stream channel and replaced it with a clear span across the entire crossing. By eliminating the piers,we found an opportunity to reduce the span by three feet in this location without affecting the flow characteristics in an adverse way. The results of our study indicate that the proposed new bridge crossings would have a positive net impact on the base flood. We determined the baseline flood elevations for the 100-year floods as 458.56 feet at bridge crossing#1 and 458.31 feet at bridge crossing#2. The change in the base flood water surface elevation at the upstream boundary of the property would be de minimus, and can be seen on the attached profile exhibit. Base flood elevations for the neighboring parcels would not be affected by the proposed new replacement bridges. We hope that our study and calculated baseline flow elevations ultimately aid in your review of the proposed new replacement bridges. Please let us know if you have any questions or require further support material. 11 of l't Best re ds, ERIC W. WOOLLEY LIC. NO. 97088 l Eric Woolley, P.E. SI a NA L �� Attached: Exhibit A—Floodplain Development Plan Exhibit B—Photographs of the Existing Stream Crossings Exhibit C—Photographs of the Characteristics of the Floodplain Exhibit D—Cross section location exhibit HEC RAS —Water Surface Profile HEC RAS —Cross sections with water surface elevations Cc: Oakencroft Holdings, LLC, Property Owner 2 In WOOLLEY ENGINEERING - g,k?y; y G ,,11 tilt7' 'vr .. �•/" ' ' t • s; ;ads �-'rf l .rd' e0R1�' - _ )ice•. - •'.42ri '; siwSY'te a t J I-- ' 4 a,s ! f ,► tr �4.! 4 c r P F�i View of existing bridge crossing location #1. 'pc L i+., � ^may '"r..k7.t , �i,. I Imo- ,,,p EMI . • , 114 j ri. ire,iat C _ � • �y. r .46 r .....be t j a .: r.• N.F `'' • , r ' , ,• ham` View of existing bridge crossing#2. Oakencroft Study 3 Exhibit B • WOOLLEY ENGINEERING t ,, _-t''i' .:, • * y t �! � 4: P G•s c� •" ,, d.. " -{ ?4+y, 'ro Lai a a " ,r 1.1 ;'skv �; to .c I N n .r f r.. '- 4 , a .7'., ., ... a .. .....1 1 . ,, . .• ,:tittei„.4.::,..t?„, . ,10., ,,,, .;_ . . . .,-. - "Re , Or 10111.1.11111 x r r, lYW 'r i: • . f ". � _ ';� ). C4*V45('y���',{ ► ',,�g SOAK i{ ] R a '• I " f ?t a �$' die'IA; y�. fr K,. K— sV • •"" View of the tributary at bridge crossing#1, looking southwest from the east abutment. Manning coefficients: 0.05 (Left Bank) 0.04 (Channel) 0.035-0.05 (Right Bank) av , 4/1141110 te e, y ;, e. it i 4 View of the tributary just north of bridge crossing#2, looking upstream. Manning coefficients: 0.05-0.06(Left Bank) 0.03-0.045 (Channel) 0.05 (Right Bank) Oakencroft Study 4 Exhibit C H1&'S ' OAoo 4ee1409*PO Gus swamp,a ulae•ua+auoa all u•op A adaui maw•Apo eaeodnd A daa iol*dm zc9s�etIvevi C'11, 7 ad64*Huaus ROA•�l�s�a�a. • • y� i. 6S I if r `_\ tiJ Y£.6S :. .� \ ........, ._. . _ir i \\ _......... - - 1 ,iv. . re*, lb.,4„,..;,.....„. '..---.... , ££-6S y ++ \ i0,.. .....---.... © - ~ _ i • • i zO =Zt 6s 9 6S . ....._.. u �� o N ''''' '''...:----' ▪ �•••• ! ....••O•• • ▪M••••••• • • 1 r. • 111110% 01•••••.a. LOOM 4,98vet usay pi,•edoe loAmu, su A. dap uo p awns a1oNI A Ip pua6ai 4igiyx3 uoigoaS sso.1 j jo.ioue ep 405 I Legend WS 100 YR-ex cond-revised WS 100YR-FINAL Ground 460 455 • 450 445- [ 4 -+ - --•--4 440 , , 0 500 1000 1500 2000 2500 3000 3500 Main Channel Distance 00 RS =6 Downstream Reach 6-Directly upstream of Bridge#1 462 < —.05 >O .05 s Legend 1- - t t WS 100 YR-ex cond-revised WS 100 YR-FINAL 460_ WS 25 YR-ex cond-revised x • i i ----------i WS 25 YR-FINAL . A WS 10 YR-ex cord-revised a •• 1 - WS10YR-FINAL • WS 2 YR-ex cond-revised WS2YR-FINAL 1 Ground ■ A Ineff 456- ♦ ♦ • e _ Bank Sta c o - 'Fs' _ > a> W - 454- 452- • \ I 450- r k .i 448 -200 -150 -100 -50 0 50 100 150 Station(ft) RS = 3 Downstream Reach 3- Directly upstream of Bridge#2 I .06 )1.Ic .05 > 462� i • Legend I S t WS 100 YR-ex cond-revised / . WS 100 YR-• FINAL 460 • t } r H WS 25 YR-FINAL WS 25 YR-ex cond-revised WS 10 YR-▪ FINAL 458- - WS 10 YR-ex cond-revised WS 2 YR-FINAL _ \��""�` \\"" �\"\\\\\\ \\_�\ ' W5 2 YR-ex coed-revised 456- `��\\\\\.,N.\\ ������•..,:\ •s.N._�''• •.., - Ground . Bank Sta 454 w 452-- 450i • 448 I J. , it j ! I 446 ; ; , I , , -500 -400 -300 -200 -100 0 100 200 300 Station(ft) MAR 0 7 2019 COMMUNITY