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Item 6 - Floodplain Storage Modificationskimley-horn.com 6160 Warren Parkway, Suite 210, Frisco, TX 75034 972 335 3580 March 22nd, 2021 Sandra Endy or Kevin Ferrer, P.E., CFM City of Southlake 1400 Main Street, Suite 320 Southlake, Texas 76092 RE:Methodist Southlake Hospital 421 E State Hwy 114 – Floodplain Storage Modifications Southlake, Tarrant County, Texas To Whom it May Concern, This letter summarizes the Floodplain Storage Modifications proposed by Kimley-Horn and Associates, Inc. (“Kimley-Horn”) for Methodist Southlake Hospital improvements. Methodist Southlake Hospital (“subject property”) is an approximately 13-acre parcel with existing healthcare facilities on the property. The existing underground detention is proposed to be replaced with an above ground detention pond. The detention pond was sized using modified rational method using the information from the record drawings. The detention pond outfall was designed to account for the tailwater from Dove Creek using a coincidental peak based on watershed size. Detention calculations are included with the construction plans. The project proposes cut and fill within the FEMA Effective Zone AE Floodplain at the proposed detention pond. The site outfalls into Dove Creek and is identified on FEMA’s Flood Insurance Rate Map Panel 48439C0085K and has a Zone AE floodplain designation assigned. See Exhibit 1 below for location of the effective floodplain relative to the subject property. Exhibit 1: FEMA Effective Floodplain Page 2 kimley-horn.com 6160 Warren Parkway, Suite 210, Frisco, TX 75034 972 335 3580 The proposed grading for the detention pond will be located at the upstream face of the State Hwy 114 frontage road within the ineffective flow area associated with the culvert crossing of Dove Creek to the east. Floodplain storage within the Dove Creek 100-YR FEMA floodplain was evaluated to ensure floodplain storage would not be decreased as a result of the detention pond improvements. A floodplain storage surface comparison was performed in AutoCAD Civil 3D using the 100-Year FEMA water surface elevation. The total amount of pre-project floodplain storage on the subject property (0.61 ac- ft) and post-project floodplain storage (1.98 ac-ft) was calculated in AutoCAD and used to determine the net change in floodplain storage (+1.37 ac-ft) due to proposed grading. Proposed grading for the detention pond can be seen on the attached Floodplain Storage Workmap. Table 1: Floodplain Storage Comparison (ac-ft) Volume (ac-ft) Pre-Project 0.61 Post-Project 1.98 Net Floodplain Storage Gain 1.37 Table 1 above shows that there is not a decrease in 100-Year floodplain storage with the proposed improvements within the subject property. If you have any questions or comments on the contents of this report, please contact me at (972) 770-1399 or carolyn.cox@kimley-horn.com. Sincerely, Carolyn Cox, P.E., CFM Cc: Caitlin Flaherty, P.E, CFM. – Kimley-Horn and Associates, Inc. Eric Mueller, EIT – Kimley-Horn and Associates, Inc. Attachments:1 – Floodplain Storage Workmap 2 – FEMA Firmette 3 – FEMA FIS Excerpts S T A T E H I G H W A Y 1 1 4 6 1 0 6 1 5 6 2 0 62 5 6 1 1 6 1 2 6 1 3 6 1 4 6 1 6 6 1 7 6 1 8 6 1 9 6 2 1 6 2 2 62 3 62 4 61 5 62 062 5 61 1 612 6 1 3 61 4 61 6 61 7 6 1 8 6 1 9 6 2 1 6 2 2 6 2 3 62 4 61 5 62 0 61 3 61 4 61 6 6 1 7 6 1 8 6 1 9 62 1 62 2 62 3 62 4 ON-SITE 100-YEAR FLOODPLAIN STORAGE: 1.98 ACRE-FT 610 615 607 608 609 611 612 613 614 616 616 617 617 615 613 614 616 617 61 5 61 2 61 3 61 4 61 6 S T A T E H I G H W A Y 1 1 4 6 1 0 6 1 5 6 2 0 62 5 6 1 1 6 1 2 6 1 3 6 1 4 6 1 6 6 1 7 6 1 8 6 1 9 6 2 1 6 2 2 62 3 62 4 61 5 62 062 5 61 1 612 6 1 3 61 4 61 6 61 7 6 1 8 6 1 9 6 2 1 6 2 2 6 2 3 62 4 61 5 62 0 61 3 61 4 61 6 6 1 7 6 1 8 6 1 9 62 1 62 2 62 3 62 4 ON-SITE 100-YEAR FLOODPLAIN STORAGE: 0.61 ACRE-FT PL O T T E D B Y MU E L L E R , E R I C 3/ 1 7 / 2 0 2 1 5 : 1 8 P M DW G N A M E \\ F R I F P 0 1 \ T X _ F R I \ F R I _ H Y D R O \ 0 6 1 1 6 3 0 0 2 - M S H D E T E N T I O N P O N D \ D W G \ E X H - F P S T O R A G E . D W G LA S T S A V E D 2/ 9 / 2 0 2 1 1 0 : 0 4 A M IM A G E S E P S G 2 2 7 6 _ D a t e 2 0 2 0 1 1 0 3 _ L a t 3 2 . 9 5 6 8 5 4 _ L o n - 9 7 . 1 4 4 4 3 6 _ M p p 0 . 1 4 9 - XR E F S X R E F x 2 4 3 6 - X R E F x A e r i a l TH I S D O C U M E N T , T O G E T H E R W I T H T H E C O N C E P T S A N D D E S I G N S P R E S E N T E D H E R E I N , A S A N I N S T R U M E N T O F S E R V I C E , I S I N T E N D E D O N L Y F O R T H E S P E C I F I C P U R P O S E A N D C L I E N T F O R W H I C H I T W A S P R E P A R E D . R E U S E O F A N D I M P R O P E R R E L I A N C E O N T H I S D O C U M E N T W I T H O U T W R I T T E N A U T H O R I Z A T I O N A N D A D A P T A T I O N B Y K I M L E Y - H O R N A N D A S S O C I A T E S , I N C . S H A L L B E W I T H O U T L I A B I L I T Y T O K I M L E Y - H O R N A N D A S S O C I A T E S , I N C . PR O J E C T N O . 06 1 1 6 3 0 0 2 DA T E : F E B R U A R Y 2 0 2 0 SC A L E : A S S H O W N DE S I G N E D B Y : E L M DR A W N B Y : EL M CH E C K E D B Y : C F C SHEET NUMBER 61 6 0 W A R R E N P A R K W A Y , S U I T E 2 1 0 FR I S C O , T E X A S 7 5 0 3 4 PH O N E : 9 7 2 - 3 3 5 - 3 5 8 0 F A X : 9 7 2 - 3 3 5 - 3 7 7 9 TE X A S R E G I S T E R E D E N G I N E E R I N G F I R M F - 9 2 8 No . RE V I S I O N S DA T E BY ME T H O D I S T SO U T H L A K E SO U T H L A K E , T A R R A N T CO U N T Y , T E X A S Not for construction or permit purposes. FOR REVIEW ONLY Engineer P.E. No.Date FEB 2020122243 CAROLYN COX FL O O D P L A I N ST O R A G E WO R K M A P NORTH PRE-PROJECT POST-PROJECT EXH LEGEND PROPERTY BOUNDARY 1-FOOT ON GROUND TOPOGRAPHY (ADAMS SURVEYING COMPANY, 2019 & AJ BEDFORD GROUP, 2011) 1-FOOT PROPOSED CONTOURS (KIMLEY-HORN, 2021) EXISTING ON-SITE 100-YEAR FEMA FLOODPLAIN PROPOSED ON-SITE 100-YEAR FEMA FLOODPLAIN 555 555 National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or DepthZone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileZone X Future Conditions 1% Annual Chance Flood HazardZone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood HazardZone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 2/28/2021 at 3:31 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 97°8'57"W 32°57'42"N 97°8'20"W 32°57'12"N Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020 F L O O D P R O F I L E S A N D I N C O R P O R A T E D A R E A S F E D E R A L E M E R G E N C Y M A N A G E M E N T A G E N C Y LEGEND 0.2% ANNUAL CHANCE FLOOD CROSS SECTION LOCATION STREAM BED T A R R A N T C O U N T Y , T X 179PSTREAM DISTANCE IN FEET FROM ESTIMATED FLOW LINE OF DENTON CREEK-GRAPEVINE LAKE D O V E C R E E K 615 610 605 600 595 230002250022000215002100020500 E L E V A T I O N I N F E E T (N A V D 8 8 ) 1% ANNUAL CHANCE FLOOD 2% ANNUAL CHANCE FLOOD 10% ANNUAL CHANCE FLOOD F G 615 610 605 600 CULVERT CITY OF SOUTHLAKE L I M I T O F D E T A I L E D S T U D Y W E S T H I G H L A N D S T R E E T S T A T E H I G H W A Y 1 1 4 S O U T H B O U N D (N O R T H W E S T P A R K W A Y ) S T A T E H I G H W A Y 1 1 4 N O R T H B O U N D (N O R T H W E S T P A R K W A Y ) S T A T E H I G H W A Y 1 1 4 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com 79 TABLE 4 – SUMMARY OF DISCHARGES (continued) PEAK DISCHARGES (cfs) FLOODING SOURCE AND LOCATION DRAINAG E AREA (sq. mile) 10% Annual Chance 2% Annual Chance 1% Annual Chance 0.2% Annual Chance Redelineation Detailed Study Streams NORTH FORK OF DEER CREEK Just upstream of Burlington Northern and Santa Fe Railroad 0.65 ** ** 700 ** SOUTH FORK OF DEER CREEK At confluence with Deer Creek 4.32 5,100 7,000 7,800 9,900 Downstream of confluence of North Tributary of South Fork of Deer Creek 4.19 5,400 7,400 8,300 10,500 Upstream of confluence of North Tributary of South Fork of Deer Creek 3.61 4,600 6,300 7,100 9,000 SOUTH FORK OF NORTH BRANCH OF DEER CREEK At confluence with North Branch of Deer Creek 2.82 3,750 5,100 5,700 7,200 DENTON CREEK At Tarrant County boundary4 3.96 6,000 8,300 9,400 36,200 Below Tributary D-l4 3.615 5,900 8,000 9,400 36,200 Above Tributary D-14 2.425 4,050 5,500 9,400 36,200 Above Tributary D-24 1.60 2,550 3,500 3,900 4,900 Above Grapevine Lake outlet channel 1.19 2,050 2,800 3,100 3,900 DOVE CREEK At Grapevine Lake 3.22 2,650 3,750 4,250 5,500 At Dove Street 2.14 2,150 3,000 3,400 4,350 At Carroll Avenue 1.51 1,850 2,600 2,900 3,700 DUTCH BRANCH At Benbrook Lake 7.30 6,900 9,500 10,900 13,800 Approximately 1.52 miles upstream of Benbrook Lake 4.90 5,700 7,900 9,000 11,300 TRIBUTARY DB-3 Approximately 480 feet upstream of the confluence with Dutch Branch 0.52 917 1,366 1,479 2,059 EDGECLIFF BRANCH Above its confluence with Sycamore Creek 6.52 5,800 8,250 9,300 11,400 Downstream of left bank tributary located east of Chelsea Drive 5.92 5,750 8,250 9,300 11,850 Upstream of left bank tributary located east of Chelsea Drive 5.04 5,050 7,250 8,150 10,400