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HomeMy WebLinkAbout1.08 Drainage reportParcel 5/1 & 5/2 Battlement Mesa PUD Preliminary Plan Drainage Report June 2005 Prepared by: Schmueser I Gordon I Meyer 118 W. 16th Street, Suite 200 Glenwood Springs, Colorado 970.945-1004 1:\2004\2004-238\COVER -DRAINAGE REPORT.DOC DRAINAGE SECTION 4:80 DRAINAGE REPORT BATTLEMENT MESA -PARCELS 5/1 & 5/2 Parcels 5/1 and 5/2 are located in the south central portion of the Battlement Mesa PUD. The parcels are bounded by Battlement Mesa Parkway on the north, County Road 308 on the east, County Road 302 on the south, and Stone Quarry Road on west. The area consists primarily of gently sloping native areas, irrigated pasture and stands of pinion, juniper and sage. Drainage patterns are generally from east to west on the site. The major drainages consist of Cemetery Gulch on the southwest and Studt Gulch on the northeast portion. Development of these parcels was contemplated in the original PUD. The level of development currently being proposed is consistent with the original plan, and downstream facilities require minimal modifications to accept these flows. FEMA NATIONAL FLOOD INSURANCE PROGRAM Cemetery Gulch, Studt Gulch and one other lesser centralized drainage were originally mapped on the 1986 Flood Insurance Rate Map (FIRM), Garfield County Panel 1315 of 1900. The Studt Gulch floodplain and central floodplain were later removed from the FIRM by Letter of Map Revision (LOMR). Only Cemetery Gulch remains as a mapped Zone A, defined as "the area of 1 OO-year flood , base flood elevations and flood hazard factors undetermined". The LO_MR application and subsequent correspondence provides key information on the hydrology and hydraulics of the area and the delineation of the regulatory floodplain for Cemetery Gulch. Reference documents include: 1. Battlement Mesa Letter of Map Revision Application, prepared by Wright Water Engineers (WWE) February 28, 1990. 2. July 20, 1992 letter from Arnold L. Mackley, Chairman, Garfield County Board of County Commissioners (BOCC) to William R. Locke, Chief, FEMA. 3. August 18, 1992 letter from Brian Hyde of CWCB to mark Bean, Director of Garfield County Regulatory Offices. 4. August 19, 1992 letter from John L. Blanchard, P.E., Wright Water Engineers to William R. Locke, Chief, FEMA. 5. October 1, 1992 response letter from William R. Locke, Chief, FEMA to Arnold L. Mackley, Chairman Garco BOCC. 6. Letter from William R. Lock, Chief, FEMA, to Marion I. Smith, Chairman, Garco BOCC. 7. Battlement Mesa Development Storm Drainage and Floodplain Study, Job No. 926.010 by Frasier and Gingery, March 1975. The 1986 FIRM and LOMR application had a specific nomenclature scheme to refer to the drainages. Cemetery Gulch was designated as Drainageway F and Basin 34 near this site. Studt Gulch was referred to as Drainageway E2a2 and Basin 26. The drainageway through the central area of this site was referred to as E2b and Basin 30. Again, only Cemetery Gulch (Drainageway F) remains as mapped Zone A under the floodplain regulations. Studt Gulch (E2a2) is still a significant drainage and must be dealt with appropriately. The central drainage 1:\2004\2004·23816·16·05 DRAINAGE REPORT.doc 1 E2b is fairly insignificant and runoff from that basin can be dealt with in a typical fashion consisting of swales, gutters and storm sewers. We should note that the WWE LOMR request considered developed conditions in hydrologic and hydraulic calculations. Parcels 5/1 and 5/2 areas were considered as being 50% impervious. This should be a fairly conservative assumption, given the currently proposed level of development. The Frasier & Gingery Master Storm Drainage Plan was also referenced in the LOMR and was included as Appendix C. The key component of that plan was that all major drainageways were designed to handle 1 aO-year flood without damage to property. The minor drainageways and storm sewers were designed based on a two-to five-year return period. When larger storms occur, pipes would surcharge and flows would be conveyed down the roads to appropriate swales and natural drainages. Another key component of the Master Drainage Plan was that "The 100-year runoff from developed areas within the project, tributary to property not owned by Battlement Mesa, Inc., shall be held to historic limits'~ The storm drainage analysis map from that study included a stormwater detention site on the Cemetery Gulch drainage just upstream of Stone Quarry Road. An approximate storage volume of 7.5 acre-feet was listed on the map. As of the writing of this report, backup information for this pond sizing has not been located. Additionally, it appears that all downstream areas to the Colorado River may have been built to accommodate developed flows. Only future development Lots 2 and 3 drain to this location. Prior to development on those two lots, a detailed analysis of downstream conditions will be conducted and an appropriate recommendation for detention pond sizing will be made. ON·SITE DRAINAGE The Master Drainage Plan exhibits show the locations of Studt Gulch and Cemetery Gulch along with locations of four on-site basins that would tend to drain in other directions. The Rational Method was chosen as the means of calculating anticipated flood peaks. The Soil Conservation Service soil study for the Rifle area shows that soils are predominately Potts loam and PottsIIdefonzo complex, which are both classified as Hydrologic Soil Group B. To be consistent with the LOMR calculations, a condition of 50% impervious area was analyzed. A weighted runoff coefficient for post-development conditions was calculated by a 50% weight of a 0.3 coefficient for open space areas in Hydrologic Soil Group B on 6%+ slopes, and a 50% weighting of impervious area at 0.95. The resultant weighted C factor was 0.625. The attached spreadsheet shows results of the on-site calculations. An additional TR-55 analYSis was also conducted using a eN of 79. These results and pertinent supporting information is attached as well. Note that the design point in Subarea 6A is contained wholly within Subarea 6. The 6A subarea represents the Lot 1 Kum & Go site draining to the northwest corner of the parking area. Hydraulic calculations for the inlet are also attached. An NPDES Stormwater Permit for construction activities over one acre will be filed 10 days prior to anyon-site construction. The plan will detail appropriate construction and permanent Best Management Practices that will be used to ensure that water quality is not degraded by the construction on Lot 1. In addition to construction BMP's, a 2500 gallon sand/oil separator is proposed prior to discharging into the storm sewer system. Kum & Go also has a detailed 1:\2004\2004-238\6-16-05 DRAINAGE REPORT.doc 2 operation, maintenance and spill management plan to lessen the likelihood of stormwater contamination. Detailed drainage plans will be prepared for Lots 2 through 5 with new Preliminary Plans for those lots. These drainage plans will demonstrate that downstream facilities have capacity for the site-specific development, or include stormwater detention. An additional NPDES Stormwater Permit will be required for each future construction project. _ 1:\2004\2004-238\6-16-05 ORAINAGE REPORT.doc 3 Battlement Mesa Parcel 511 & 512 PRELIMINARY PLAN RATIONAL METHOD DRAINAGE CALCULATIONS (DEVELOPED CONDITIONS) SUB-A~'" TOTAL IMPERV. PERVIOUS PERVIOUS AVG. AREA· TIME OF 2-YEAR NUMBER AREA(SF) AREA(AC) AREA(%) AREA(%) RUNOFPC' RUNOFF'C' COEFF CONC.(MIN INTENSITY (IPH) 3 365523 8.39 50 50 0.30 0.625 5.24 16 1.53 • 1094265 25.12 50 50 0.30 0.625 15.70 20 1.30 5 150992 3.47 50 50 0.30 0.625 2.17 14 1.67 • 670873 15.40 50 50 0.30 0.625 9.63 15 1.62 6a 67713 1.55 95 5 0.30 0.918 1.43 5 2.70 2-YEAR 25-YEAR 25-YEAR Q (CFS) INTENSITY (IPH) Q (CFS) 8.02 3.30 17.31 20.41 2.B7 45.06 3.62 3.59 1-78 15.59 3.41 32.82 3.85 5.50 7.84 100-YEAR 1OG-YEAR INTENSITY(IPH) QICFS) 4.37 22.92 3.81 59.82 4.70 10_18 4.58 44.0 • 7.67 10.94 Job # 2004-238.001-20 6117105 BMPARCE~1&5-2_drainage.xfs SGM,lnc. David M. Katz. P .E. ~ .... \0 ~ to W r LAND USE OR SURFACE CHARACfEmSTICS UNDEVELOPED AREAS Bueground CultivatcdlAgricuItural Pasture Meadow F ...... RESIDENTIAL AREAS 111 acre per unit 114 acre per unit 113 acre per unit 112 acre per unit 1 acre per unit MISC. SURFACES Pav.:ment and roofS TPlIic areas <010;1 and pvel) NOTES: 1. 1. 3. ,r '( " as basic _".pe, homo£enelty of surfaC-f: type. sUI-faa depftSSlon stonge. and .. hI£her .. .uowInc use or. "e-value In the low ranee. Conversely, ptrunlt, .... also lor commercial .... bulustrtaI areas,1IIe values under MlSC RATIONAL METHOD RUNOFF COEFFICIENTS from Table 4, UC-Davls, which aDDean to be a modifICation of work done TABLE "B-1" r ~,"-, -, -""-I-~--'I-·~---··"·'--r·'-"··"·····h -', .... "",'--,cl-;--''''--IT~-ITJ-m''l''''':-]-r I ,! I! I I I ' ,I. . t ./, . , . , 1 • • • , , , • ; , • • • 1 • • .1_ 'I'o.j -1of' I. l I 'I I I" l ,I • ! I I I •• I •• : I ..•• I •••••• I :; I • I I' /' I I ;, :: •. I I ',I I : i I I I : I I •• i , I I I .! .. I I. 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DMK sub-Area Identifier/3 4 5 6 SHEET SHALLOW SHALLOW CHANNEL SHEET SHALLOW SHALLOW CHANNEL SHEET SHALLOW SHEET SHALLOW SHALLOW CHANNEL Flow Length (tt) 99 200 900 470 99 300 2000 400 99 600 99 300 1000 500 Battlement Mesa 5/1 & 5/2 Post-development conditions Garfield County, Colorado Sub-Area Time of Concentration Details Mannings's Slope n (tt/tt) 0.0400 0.150 0.0600 1.3 0.0600 1.3 0.0400 0.012 End Area (sq tt) 3.14 Wetted Perimeter (tt) 6.28 Velocity (tt/sec) 16.319 Time of Concentration 0.0400 0.0600 0.0630 0.0200 0.0400 0.0660 0.0400 0.0670 0.0530 0.0500 0.150 1.3 1.3 0.012 0.150 1.3 0.150 1. 300 1. 300 0.012 3.14 3.28 15.873 Time of Concentration Time of Concentration 3.14 6.28 17.361 Travel Time (hr) 0.193 0.014 0.050 0.008 0.265 :::"""'''''''='''= 0.193 0.021 0.109 0.007 0.330 0.193 0.040 0.233 0.193 0.020 0.059 0.008 Time of Concentration 0.28 TR-55, Version 2001.00.07 page 1 6/16/05 2:22:04 PM OMK Sub-Area or Reach Identifier SUBAREAS 3 4 5 6 REACHES OUTLET Peak 2-Yr (cfs) 1.21 3.18 0.54 2.16 6.95 TR-SS, version 2001.00.07 Battlement Mesa 5/1 & 5/2 Post-development conditions Garfield County. Colorado Watershed Peak Table Flow by 2S-Yr (cts) 4.31 11.54 1.88 7.70 25.13 Rainfall lOO-Yr (cts) 7.56 20.39 3.29 13.58 44.30 page Return Period 1 6/16/05 2:~1:13 PM User: Project: SubTitle: State: County: Filename: Name 3 4 5 6 TR-55 Current Data Description ---Identification Data ---DMK Date: Battlement Mesa 5/1 & 5/2 Units: Post-development conditions Colorado Areal Units: Garfield r,\2004\2004-238\BM5-1&5-2.w55 ---Sub-Area Data ---Description Reach Outlet Outlet Outlet Outlet Area (ac) 8.39 25.12 3.47 15.4 Total area: 52.38 (ac) ---Storm Data Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 2S-Yr 50-Yr (in) (in) (in) (in) (in) 1.3 1.5 1.7 1.9 2.2 6/16/05 English Acres RCN 79 79 79 79 100-Yr (in) 2.4 Storm Data Source: Rainfall Distribution Type: User-provided custom storm data Type II Dimensionless unit Hydrograph: <standard> TR-55, Version 2001.00.07 Page 1 6/16/05 Tc 0.265 0.330 0.233 0.28 l-Yr (in) 1.1 2:21:21 PM DMK Sub-Area or Reach Identifier SUBAREAS 3 4 5 6 REACHES OUTLET Peak 2-Yr (cfs) (hr) 1.21 12.11 3.18 12.15 0.54 12.08 2.16 12.11 6.95 Battlement Mesa 5/1 & 5/2 Post-development conditions Garfield County, Colorado Hydrograph Peak/Peak Time Table Flow and Peak Time (hr) by Rainfall Return Period 25-Yr lOO-Yr (cfs) (cfs) (hr) (hr) 4.31 7.56 12.07 12.07 11.54 20.39 12.12 12.09 1.88 3.29 12.06 12.05 7.70 13.58 12.09 12.08 25.13 44.30 TR-55, Version 2001.00.07 Page 1 6/16/05 2:09:54 PM •• m • a. ::l 0 '-C) -.-0 en .(-J 0') -0 0 '-"C ~ J: <0 -.:::t N 0 ro <0 -.:::t N 0 ro ro ro ro ~ ~ ~ ~ ~ JaqwnN aAJn:> o <0 0 L.{) 0 -.:::t 0 ("I') 0 N o 0~ en ::::l .0c-: a> Co -E NOTE: When specifying or ordering grates-Please refer to "CHOOSING THE PROPER INLET GRATE" on pages 108 and 109. ~-3292 )urb Inlet Frame, Grate and Curb Box Heavy D'IiY Also available with flat mountable curb plate, grated or solid, as shown on R·3246-1, in place of curb box. F"~"~ 35 1/4' 15 112' 1 314' CURB BOX ADJUSTABLE 8' TO " ~~ ~". w~ ~~Ia I------... -----~ 1+---31·------1. R-3295 Curb Inlet Frame, Grate, Curb Box Heavy Duty I 37 eJI8' 3lI 1/4' I -"1--, II" " .---,.. "" = I 331Je" I 43'''' "--_ ... _ =~!Wl(. '-----".-----1. R-3295-2 Double Unit Frame, Grate, Curb Box Heavy Duty 162 NEENAH·"iX~ FOUNDRY COMPANV ~~ ,L'tQ J'; I...i. ., A-~ ,/.1 51 p:: el3 f.,. '.i.. 1 ,i'' .' \' , . ' : T I I 7 /I 1/I GRATE OPENING RATIO t/I I //1//_. P-I-7/S-4 O.S I---P+7/S 0.9 ~'l I-I II/I . • P-I-I/S 0.6 7 y i., 7/~ Reticuline O.S • Curved vone 0.35 10 S 6 5 4 I---300 tilt-bar 0.34 I I I II 171~~ [7!//~@3 • Tested I II //II II II I I ///2 .. V~ ~ I /' ~ ~ O.S 6 . V.........:: ~ W///5 /V L0 I?::: t7: ~ . CURS '" I I T ~~~~r:::: V-I I W ./' '/'/1::/I I 1 31---~~ 1::71717 I I ~~~~v j t--L --t A = CLEAR OPENING AREA ~~v P = 2W + L (WITH CURB) .p =2(W+L) ( WITHOUT CURB) . I I I I '" o. lI!i:I O. 6'V 0 .4 O. 0.2 O. 2 3 4 5 6 8 10 20 30 40 50 60 80 100 DISCHAII6E Q 1FT 3/S1 CHART 11. Grate inlet capacity in sump conditions. t....-6 1~I...Lr Q'2-S:: 7· ~'( CAtS tilt tJA. II t ~ ~ l,.q ~ -z..,. U5t.. ClA12(J BDY oR. (It..D66 /~6 /VI Lt S '/f>£ {b).J510t~ to (2~ -S/P,,?,,) 'D()A ~t..t IPL-~ r 71 lr)t?Jo u--066,ltJ6 -'> p;-7.0..,' Project Description Worksheet Flow Element Method Solve For Input Data Mannings Coefficient Diameter Discharge Results Channel Slope Depth Flow Area Wetted Perimeter Top Width Critical Depth Percent Full Critical Slope Velocity Velocity Head Specific Energy Fraude Number Maximum Discharge Discharge Full Slope Full Flow Type BA TILEMENT MESA 5/1 & 5/2 Worksheet for Circular Channel K & G OUTLET Circular Channel Manning's Formula Full Flow Slope 0.012 15.0 in 7.84 cfs 0.012552 ftlft 1.25 ft 1.2 ft2 0.00 ft 0.00 ft 1.11 ft 100.0 % 0.011213 ftlft 6.39 ftls 0.63 ft 1.88 ft 0.00 8.43 cfs 7.84 cfs 0.012552 ftlft NIA Notes: 25-YR DESIGN SLOPE> 1.26% untitled.fm2 Schmueser Gordon Meyer 06/17/05 12:56:36 PM © Haeslad Methods, Inc. 37 Brookside Road Waterbury. CT 06708 USA Project Engineer: David M. Katz FlowMaster v7.0 [1.0005] +1-203-755-1666 Page 1 of 1 . I· f .' f , i FLOOD ",-.' J " • ( ,Ii ~,/,.; -/HOWNl/N. , SIS • t'l, .):/" I. \' ) '. ... .. ;"... i DENSITY, REl!lD~tN ). 'I \ •..•. -. '") .. :.' 'C HIGH SCHOOL /;. /, r· .... 1-'.l.,-..... +lI-I,..;~ ... ,....-_"' .... -f _ .• -~\, //I I "~ /1 , I \ -. MEDlU". OfSITY RESioE~TIA'l I . " I ~ .J .. ' ' . I ,lli .! 1 4 '~~4' I .. ',-, II \ .. ~" .\ " ~, ~ . ~ .,., '-c " ,-, .. :.I '",n' • ". ,,. I-I" 1 \ . I I ~ MEDIUM' DENSITY //.. I .. .~ .. ~jiiiii ... -~!It ••;; .f( III(./'• •_ .~...... '. ..... . ,I ,"f . .. · , GARFIELD COUNTY Board of County Commissioners MARIAN SMITH Glenwood Springs 81601 ARNOLD MACKLEY Rifle 81650 BUCKEY ARBANEY Glenwood Springs 81601 William R. Locke, Chief Risk Studies Division Federal Insurance Administration Federal Emergency Management Agency Washington, D.C. Case No. 90-08-24P RE: FIRM Panel 080205-1315B Garfield County, Colorado Dear Mr Locke: July 20, 1992 COUNTY COURTHOUSE 109 8th Street Suite 300 Glenwood Springs. CO 81601-3303 Telephone: (303) 945-9158 (303) 625-5571 CHUCK DESCHENES County Administrator Last year, Garfield County requested that FEMA remove the floodplain delineations for certain drainageways on FIRM Panel 080205-1315B. FEMA approved the removal of the requested drainageways by correspondence issued on February 26, 1991. By this letter, the Garfield County Board of County Commissioners is requesting the removal of drainageways noted in correspondence to you, dated May 12, 1992, from John Blanchard, Wright Water Engineers. As noted in our previous correspondence, we feel FEMA and Garfield County did not have sufficient and technically correct information to make the original Zone A delineations on the FIRM. Your cooperation in resolving this matter will be appreciated. If you have any questions or concerns regarding this matter, you may call or write to Mark Bean, Director of Regulatory Offices. Sincerely, ~r<:~ Arnold L. Mackley, Chairman Garfield Board of County Commissioners ALMIsa COLORADO WATER CONSERVATION BOARD Department of Natural Resources 721 Siale Centennial Building 1313 Sherman Street Denver, Colorado 80203 Phone 13031 866-3441 STATE OF COLORI\D( FAX f3031866-2115 August 18, 1992 Rov Romer Goveornor Mr. Mark Bean Director of Garfield County Regulatory Offices 109 8th Street, Suite 303 Glenwood Springs, CO 81601 Dear Mark: We have received and reviewed the submittal prepared by Wright Water Engineers requesting a Letter of Map Revision (LOMR) for the Battlement Mesa portion of Garfield County. As you know, this request proposes additional changes to the county's Flood Insurance Study (FIS) in the Battlement Mesa area beyond those changes already approved by FEMA in 1991. In 1991 FEMA approved the removal from the FIS of floodplain delineations for several drainages in Battlement Mesa. The objective of the current LOMR request is to have FEMAapprove the removaL from the FIS of-floodplain delineations for some additional drainages. As was the case in 1991, the basic premise is that the original delineations were in error and did not meet FEMA's technical criteria. For that reason Wright Water Engineers (WWE) is identifying errors in the delineation of the flood hazard at the Battlement Mesa site at the time the FIS Was bein2 prepared_ Although regrading, drainage and flood control improvements, street crossings, and other changes brought about by urbanization have altered or virtually eliminated some of the floodplains affecting Battlement Mesa, WWE is not examining or delineatin2 the floodplain as it would be today. Six drainages were identified in the LOMR request. They are all part of the major drainage basin labelled "E". Two subbasins ("E2A1AH and "E2AlB"), basins "E2A1" and "E2A2", and basin "E2B" are all very close to each other. They are part of basin "E2". Basin "E1A", is, in turn, part of the larger basin, HE1". "E1A" is about a mile further north than the other basins. All are in the same general area as the five drainages that were part of the 1991 LOMR request. Our office commented on the 1991 LOMR request, which was a very similar request. On January 11, 1991 I sent a letter to Mr. John Matticks, Chief of the Risk Studies Division of the Federal Insurance Administration regarding WWE's request that the delineations of floodplains for several other drainages in the same portion of Battlement Mesa be removed. , , Mr. Mark Bean August 18, 1992 Page two In that letter I raised concerns about the map scale used, about inaccuracies in drainageway alignments, about the size of drainage basins, and about the lack of updates in the 1986 FIS to reflect topographic changes made in the early 1980's. FEMA eventually issued a LOMR removing floodplain delineations for those drainages. The same concerns apply to the current list of six drainages being submitted to FEMA We agree with WWE's conclusion that floodplains should not be delineated on the Flood Insurance Rate Maps (FIRM's) for the six drainages. We reco=end that the floodplain delineations for those drainages be removed from the FIRM's and that they be regulated by Garfield County as local drainages. Should FEMA agree with WWE's findings, the likely outcome would be a LOMR rather than a Physical Map Revision. For reasons that go beyond the changes at Battlement Mesa, we would prefer to see a Physical Map Revision for Garfield County. You and I have discussed the fact that we are currently working with the Sacramento District of the U.S. Army Corps of Engineers to complete a floodplain information report for the Colorado River from Glenwood Springs to the Mesa County line (and then into Mesa County). In addition, you already have three floodplain information reports prepared by the USDA Soil Conservation Service for various streams that are tributary to the Colorado River. Once the Colorado River mainstem report is ready, we trust that FEMA will be able to physically revise Garfield County's FIS to incorporate all of those reports. When the FIS is revised to include all of that new floodplain information, the Battlement Mesa changes should be made as 'Well. At the appropriate time your office and Battlement Mesa Partners-should provide plats and any other information to assure the inclusion of current roads and other relevant physical features on the revised FIS. A revised FIS for Garfield County should show conditions as they are in 1992 rather than as they were 5 or 10 years ago. We hope that the FIS will be physically revised in the near future. Meanwhile let me know if you have any questions or concerns regarding the LOMR request. Sincerelv, ~ Brian R. Hyde cc: William Locke, FEMA, Washington, D.C. Virginia Motoyama, FEMA, Region VIII Bill Wilde, Battlement Mesa Partners John Blanchard, WWE Bill Lorah, WWE WAf Wright Water Engineer.;, Inc. DENVER OFFICE 2490 West 26th Ave., Suite 100 A Denver, Colorado 80211 FAX (303! 480·1020 (303 480·1700 Mr. William R. Locke Chief, Risk Studies Division August 19, 1992 Federal Insurance Administration Federal Emergency Management Agency Washington, D.C. 20742 GLENWOOD SPRINGS OFFICE 618 Colorado Avenue P.O. Box 219 Glenwood Springs, Colorado 81602 FAX (303)945·9210 Denver Lin. (303) 893·1608 (303) 945·7755 Re: Case No.90-08-24P, Battlement Mesa PUD, Garfield County, Colorado Wright Water Engineers, Inc. (WWE), on behalf of our client Battlement Mesa Partners, (BMP), hereby respectfully submits supplemental information for our request of a Letter of Map Revision (LOMR) for FEMA-regulated drainageways situated within the Battlement Mesa Planned Unit Development as shown on FIRM Panels 080205-1315B for Garfield County, Colorado. BACKGROUND The original Battlement Mesa LOMR was submitted under cover dated February 28, 1990 to request abrogation of FEMA floodplain jurisdiction from numerous local drainag~ways traversing the development. These drainageways typically receive stormwater runoff from basins less than 250 acres and are generally: considered minor, local tributaries to the Colorado River. FEMA correspondence issued on August 6, 1990 acknowledged acceptance of the WWE computed flood flow hydrology by FEMA's Denver regional office and the Colorado Water Conservation Board (CWCB), but noted that drainageways would not be removed from FEMA jurisdiction unless technical data was submitted to demonstrate the current FIRM information was incorrect. Supplemental information was subsequently submitted on January 24, 1991 for several drainageways in Section 8, Township 7 South, Range 95 West, of the Sixth Principal Meridian. Using 1980 aerial mapping to establish a common basis for comparison with mapping used by FEMA contractors in floodplain delineations across the site, HEC-2 backwater analyses were performed to demonstrate the inaccuracy of floodplains depicted a FIRM panels. On February 26, 1991 FEMA. issued correspondence to the Garfield County Board of Commissioners (copy attached for reference) to officially abrogate and remove Drainageways E1B1A1, EIB1A2, EIB2A1, EIB2A2 and EIB2B from FEMA regulation and FIRM mapping. The purpose of this submittal is to present supplemental floodplain information relating to other similar Battlement Mesa drainageways located in Section 8 and Section 17, Township 7 South, Range 95 West and request removal of six additional FIRM drainageways. Figure William R. Locke August 19, 1992 Page 2 1 shows the location of these drainageways designated as E1A, E2A1, E2A1A, E2AlB, E2A2, and E2B. HEC-2 backwater analyses, utilizing the hydrological data previously approved by FEMA and the CWCB (summarized in Table 1), are again employed here to demonstrate basic errors contained on the effective FIRM panels. Aerial mapping from 1980 again serves as a basis for comparison with FEMA contracted work. Summary of Pertinent FEMA and CWCB Approved Hydrology TABLE 1 Designated Basin Area Q100 Drainageway (Ac) (cfs) E1A 90 180 E2A1 262 325 E2A1A 70 150 E2A1B 179 175 -E2A2 -.129 255 E2B 38 70 DEMONSTRATION OF ERRORS IN FIRM DELINEATIONS FOR DRAINAGEWAYS E2A1,E2A1A.E2AIB.E2A2,~D E2B Delineations of the computed 100-year floodplains for the subject drainageways are contrasted with current FIRM regulated floodplains on the attached Sheets 43, 48, 58, 59, 71 and 72. In all cases, the computed floodplain is more narrow (and, hence, more shallow) than the overlain FIRM floodplain boundary. As shown by the accompanying HEC-2 summary printouts, the flow regimes for these five, relatively steep, channels is critical. The floodplain delineations, therefore, conservatively reflect critical depths of each cross section for all study reaches. Other errors in the FIRM panels, identified in previous submittals, are restated below for background information; 1. The subject FIRM panels utilized an enlargement of 2,000 scale USGS topographic mapping with forty-foot contour intervals to obtain a scale of oneinch equals fifty-feet and two-foot contours. Although more detailed base William R. Locke August 19, 1992 Page 3 mapping for this area was available from local sources, FIRM floodplain delineations are based on very coarse mapping. 2. The subject FIRM panels do not show land form changes and land development improvements that existed as early as 1980. Planimetric and topographic changes, including new collector roadways (e.g. Battlement Mesa Parkway and Spencer Parkway), modified drainageways, and other land development improvements, are not shown or considered by current FIRM information. 3. The regulated drainageways as shown on the FIRM panels are substantially wider and of different horizontal alignment than those existing in the field. The large scale USGS topographic mapping and approximate hydrological techniques utilized by FEMA likely produced these errors. 4. The CWCB did not designate nor approve the 1977 FIRM panels because the engineering work upon which the floodplains were based was not done to normal engineering standards acceptable to the State authority. 5. The CWCB did not designate nor approve the 1986 FIRM panels for the same reason they did not approve the 1977 panels. Acopyofthe January 16, 1986 resolution of the CWCB is attached to confirm the fact that these floodplains were not approved nor designated by the State. 6. The Battlement Mesa floodplains shown on the 1977 and 1986 FIRM panels are schematic only, approximate in delineation, and do not represent a standard of engineering practice generally employed in designating Colorado floodplains. Standard practice includes obtaining the approval of the CWCB of the engineering parameters and proposed floodplains prior to FIRM panel preparation and designation as a regulated drainageway. Also enclosed are copies of letters provided by the Garfield County Board of County Commissioners and Mr. Brian Hyde of the CWCB expressing the County's and State's position, respectively, regarding this matter. Both regulatory entities are concerned with the existing FIRM panel errors and are supportive of the LOMR request. Because of the uniqueness of this LOMR application and the duration of the ongoing review process, we respectfully request that FEMA contractor Michael Baker and Associates be assigned to continue the review under this submittal. This application deals with complex issues that require an awareness of previously submitted information and understanding of the basis for prior removal of drainageways by FEMA in February, 1991. William R. Locke August 19, 1992 Page 4 SummaO' Due to the fact that the January 3, 1986 FIRM panels have been shown to contain erroneous flood risk information by the attached technical data, that the LOMR request is endorsed by the CWCB and Garfield County, and that the floodplain characteristics of Drainageways E1A, E2A1, E2A1A, E2AlB, E2A2 AND E2B are comparable to those abrogated in February, 1991, WWE requests that a supplemental LOMR be issued for FIRM Panel 080205-1315B to remove said drainageways from FEMA floodplain regulation. Very truly yours, WRIGHT WATER ENGINEERS Attachments cc; Mr. William Wilde, Battlement Mesa Partners Mr. Mark Bean, Garfield County Planning Department Mr. Brian Hyde, Colorado Water Conservation Board WUJlB/= 811.()63.100 baltlcmcn \case\iIb ....... ., FIGURE 1 Battlement Mesa Location Map U.S.G.S. 7 1/2 minute series Grand Valley Quad (1962) Scale: 1"=2000' water Engineers April r I 1992 " ~ /11/-'-------1 I I I I 5129\ ----'< (~ _/!iBa~t ~~--: _l Sch -'-----_:.::~ /r . \ \ '-_/. . 5'~", •. --in place 5/40 ) \ ---~'y< "---\ i . ....., r--J:...--:/~ oo:t;e;:~:::' ;,:;.~ 1~ttL~~ .~ . . Federal Emergency Management Agency Washington, D.C. 20472 CERTIFIED MAIL RETURN RECEIPT REQUESTED The Honorable Arnold L. Mackley Chairman, Garfield Board of County Commissioners 109 Eighth Street, Suite 300 Glenwood Springs, Colorado 81601 Dear Mr. Mackley: IN REPLY REFER TO: 102A Case No.: 92-08-054P Community: Garfield County, Colorado Map Panel Numbers: 080205 1315 B Effective Date of This Revision: 080205 1705 B OCT ·11992 chis is in response to a lettet dated August '19, 1992, trom Mr. John L. Blanchard, P.E., Project Engineer, Wright Water Engineers, Inc., (WWE) , regarding the effective· Flood Insurance Rate Map (FIRM) for the unincorporated areas of Garfield County, Colorado. In his letter, Mr. Blanchard requested that we revise the effective FIRM to show the effects of a detailed hydrologic and hydraulic analysis along drainageways identified as E1A, E2B, E2Al, E2AIA, E2AIB, and E2A2 on Figure 1 submitted with this revision request and entitled "Battlement Mesa Location Map," prepared by WWE, dated April 1992. All data necessary to support the request were submitted with the August 19, 1992, letter, and with data submitted with the earlier revision request for drainageways in Garfield County, Colorado, shown on Panel 1315 B, and approved by a Letter of Map Revision (LOMR) dated February 26, 1991. '. We have completed Our review of the submi t ted data wi th regard to the data used to produce the effective FIRM and have revised the FIRM to modify the floodplain boundary delineations of a flood having a I-percent probability of being equaled or exceeded in any given year (base flood) along the drainageways identified as E1A, E2A1, E2A1A, E2A1B, E2A2, and E2B on the above-mentioned figure in the vicinity of Battlefield Mesa. Flooding on these drainageways is no longer shown on FIRM Panels 080205 1315 Band 1705 B based on minimal resulting topwidth of the 100-year floodplain and depth of flow. (The G~6rage topwidth 15 42 feet; av~rage depth of flow, 1.8 feet.) The modifications are shown· on the enclosed annotated copies 080205 1315 Band 1705 B. This LOMR hereby revises these effective FIRM dated January 3, 1986. of FIRM Panels panels of the Because of current funding constraints, we must limit the number of physical map reV1Slons. Consequently, we will not ·publish a revised FIRM for Garfield County to reflect modifications at this time. However, if in the future we revise and republish the FIRM panels affected by this LOMR,· we will incorporate the previously described modifications at that time. These modifications have been made pursuant to Section 206 of the Flood Disaster Protection Act of 1973 (P.L. 93-234) and are in accordance with the National Flood Insurance Act of 1968, as amended (Title XIII of the Housing and Urban Development Act of 1968, P.L. 90-448), 42 U.S.C. 4001-4128, and 44 ,. , ' 2 CFR, Part 65. As required by the legislation, a community must adopt and enforce floodplain management measures to ensure continued eligibility to participate in the National Flood Insurance Program (NFIP). Therefore, your community must enforce these regulations using, at a minimum, the base (100-year) flood elevations, zone designations, and floodways in the Special Flood Hazard Areas shown on the FIRM for your community, including the previously described modifications. This response to your request is based on minimum floodplain management criteria established under the NFIP. Your community is responsible for approving all proposed floodplain developments, including thi s request, and for ensuring that necessary permits required by Federal or State law have been received. With knowledge of local conditions and in the interest of safety, State and community officials may set higher standards for construction, or may limit development in floodplain areas. If the State of Colorado or Garfield County has adopted more restrictive or comprehensive floodplain management criteria, these criteria take precedence over the minimum NFIP requirements. The community number and suffix code listed above will be used for all flood insurance policies and renewals issued for your community on and after the effective date listed above. The modifications described herein are effective as of the date of this letter. However, a review of the modifications and any requests for changes should be made within 30 days. Any request for reconsideration must be based on scientific or technical data. This LOMR will not be printed and distributed to primary map users such as l()cal ins\ll-arice agents and morEgagere"dersltheref()re,-Uie community wi 11 serve as a repository for these new data. We encourage you to disseminate the information reflected by this LOMR widely throughout the community in order that interested persons such as property owners, insurance agents, and mortgage lenders may benefit from this information. We also encourage you to consider preparing an article for publication in the community's local newspaper that would describe the changes that have been made and the assistance the community will provide in serving as a clearinghouse for these djta and interpreting NFIP maps. Please note that the Federal Emergency Management Agency (FEMA) is currently developing detailed application and certification forms for use in requesting revisions or amendments to NFIP maps. These forms are mandatory for all requests received by FEMA on or after October 1, 1992. The forms will facilitate an efficient review by highlighting relevant technical considerations; there tore, use of' these forms prior to that date, while voluntary, is strongly recommended. 'Application forms are presently available for Letter of Map Amendment and LOMR Based on Fill requests, and should be available October 1 for all other revision requests. ., 3 If you have any questions regarding the modifications described herein, ease call the Chief, Natural and Technological Hazards Division, FEMA, in _cover, Colorado, at (303) 235-4830, or Mr. Karl Mohr of my staff in Washington, D.C., at (202) 646-2770. Enclosures cc: Mr. Brian R. Hyde Colorado Water Conservation Board Mr. John L. Blanchard, P.E. Project Manager Wright Water Engineers, Inc. Mr~liam W. Wilde, P.E. ~e~~~r of Operations Sincerely, William R. Locke Chief, Risk Studies Division Federal Insurance Admini9tration I:J <"'> C> 2.:zr ''"" ~ ~ c: -'» :":"; t~:= iz .... c: ~~ 0 l>'" :o~ 0"" C) -< ... N~ -' O~_ ~.... ~"" "-'"c": ..... ,'" w'" ~ -", I:D!=:' '"", ~-t..11Y11 I vr //STUDY ,/;A REVISE -~.-I -ZONE A \ MIT OF STUDY ~ i'"'M -r"'I rrr'I ~ ---4 ~ ~ 2()C) 20;.-~ ~5~ ---~ 0:<l-"';.-rr1 ~ dOt""" ~ "> '0(°) ~ ;;i 0 .. .,.:.= >'" cZ: ''"" ..., c:;::) > :< ~ E ZONEC LIMIT OF STUDY ~ "" x ~-~ g;la ~ c; ::3: x := z -'" ~ <:: 0 0 ... 0 z> -;; <"> .... -c~ ~ ... x ..>.....-.. ::l -~ '" 0 .>..-. -n .~, , I. APPROXIMATE SCALE IN FEET 1000 0 \ E"3 E3 uOY REVISED TO REFLECT LOMRDATED FEB26 1991 ~---IT OF STUDY FLOOD BOUNDARY NOT SHOWN TO SCALE LIMIT OF STUDY ZONE C I ---r-------------~!; -----~ ZONEA --"-'---LIMIT-OF STUDY LIMIT OF STUDY Zt-•• E C HNS PANEL 1 AREA REVISED [}ill (]ill /ZONE A 17 AREA REVISED--.J \ \ I----+--;L" M"" ;TT~O'F STUDY ~' LIMIT OF STUDY Q][] /~ ~ ~LlMIT OF STUDY 16 ~ -.-.......•... .~ -s. _ ._. .... ~~~~-:~~rL1~J:r,". ' ~___ 1000 APPROXIMATE 0s eAL( IN FEfT 100( ._..-C .L J1s ~ E3 ~'I ~ _ ,,_St()n. .OVO' ~'J-20~~~ '--, LIMIT OF STUDY nllllllllllllill NATIONAL flOOD INSURANCE PIO;UM '~ \ -,-. -FIRM FLOOD INSURANCE RATE MAP GARFIELD COUNTY, COLORADO (UNINCORPORATED AREAS) PANel 1705 OF 1900 ""',...''1'" ... ·""'n" ''''-'O'~' ''', 0\'." \ .. . ~"f' s,~ if' ,'>( ~ ~ :,., R ''''", it • ~ a:. a , ~·\lt"'l ~olilT l .,r. .. ~ 2:~-~lA.\t .-•.. ...,· .. 8 ~]~JnpCT 1 1992 CoMMUHITY-PAHEL NUMBER 080205 1705 B MAP REVISED: JANUARY 3, 1986 "!HR 5 . 31 Federal Emergency Management Agency Washington, D,C, 20472 CERTIFIED MAIL RETURN RECElPT REQUESTED The Honorable Marian I. Smith Chairman, Garfield County Board of , Commissioners 109 Eighth Street, Suite 300 Glenwood springs, Colorado 81601 .' -.. -...•.. '-, --..... Dear Ms. Smith: IN REPLY REFER TO: 102A Community: Garfield County, Colorado (Unincorporated Areas) Map Panel Number: 080205 1315 B Effective Date ---.. of Ynis--Revi"ion: FEB 2 6 i991 This is in response to a letter dated January 24, 1991, from Mr. William L. Lorah, P.E., Vice President, and Mr. John L. Blanchard, P.E., Project Engineer, both of Wright Water Engineers (IIWE) regarding the effective Flood Insurance Rate Map (FIRM) for the unincorporated areaS of Garfield County, Colorado, dated January 3, :986. In their letter, Mr. Lorah and Mr. Blanchard requested that we revise the effective FIRM to show the effects of a detailed hydrologic and hydraulic analysis along drainageways identified as Elblal, Elbla2, E1b1b, Elblal, Elb2a2, "'and Elb2b on Figure 1 of the submit tedre-porteri-t i ned' "Bat\: lemenf' Me9a Lifn er-'ofMapRevision- ,"'p-repareo by \/WE, dated February 1990. These data were submitted to support the initial request for a Letter of Map Revision (LOMR) from Ms. Sheila A. Beissel, Project Engineer, \/WE, and Mr. Lorah with their letter dated February 28, 1990. Ms. Beissel and Mr. Lorah submitted all the data necessary to review thi S reques t wi th letters dated February 28, April 11, June 22, 1990, and January 24, 1991. We have completed our review of the submitted data with regard to the data used to produce the effective FIRM and have revised the FIRM to modify the floodplain boundary delineations of a flood having a I-percent probability of '-"being-equaled or' e%c""ded-1,·n lITI'y·"gi-ren-Yell'r (base, flood) along drainageways . " identified a5_-Elblal,.~1b-l'a2, Elb1b; Elb2al; Elb2a2, and Elb2b in the abovereferenced report in the vicinitY-'of Battlement Hesa. Of these drainagevays, El-bTaT, .;El-bh:Z-, E1b2al,. Elb2a2, and E1b2b have been removed based on the topwidth of the 100-year floodplain and depth of flow (average topwidth 35 feet; average depth 1.5 feet). The tOO-year floodplain for drainageway Elblb has been redelineated based on the revised hydraulic analysis. The modifications are shown on the enclosed annotated copy of FIRM Panel 080205 1315 B. This LOMR hereby revi ses this panel of the effective FIRM dated January 3, 1986. ·.t:)40" ~"~ ,:::,,... ... HAP. ., r'lH? 5 "31 8: 18 F F:( PAGE.OG3 -2 Because of current funding constraints, we must limit the n~ber of physical map reVl.,ons. Consequently, we will not publish a revised fIRM for Garfield County to reflect modifications at this time. However, if in the future we revise and republish the FIRM panel affected by this LOMR, we will incorporate the previously described modifications at that time. These modificat ions have been made pursuant to Section 206 of the Flood Disaster Protection Act of 1973 (P.L. 93-234) and are in accordance with the National Flood Insurance Act of 1968, as amended (Title XIII of the Housing and Urban Development Act of 1968, P.L. '90-448), 42 U.S.C. 4001-4128, and 44 CFR, Part 65. As required by the legislation, a community must adopt and enforce floodplain management measures to ensure continued eligibility to participate in the National Flood Insurance Progr./lm (NFIP). Therefore, your community must enforce these regulations using, at a minimum, the base (lOa-year) flood elevations, zone deSignations, and floodways in the Special Flood Hazard Areas shown on the FI~~ and Flood Boundary and F100dway Map for you:: CQDl!lIUll.1tY-r-.incl udi"g-,-t~ !>Ceviol>siy-d-es-.:ri.bed· lIK>d-iHcat ions. This response to your request is based on minimum floodplain management criteria established under the NFlP. Your community is responsible for approving all proposed floodplain developments, including tb.is requesC', and for ensuring that necessary pennits required by Federal or State law have been received. Wi th knowledge of local cond ieions and in the interest of safety, State and community officials may set higher standards for construction, or may limit development in floodplain areas. If the State of Colorado or Garfield County has adopted more restrictive or comprehensive floodplain management criteria, these cr~teria take precedence over ,the mini!1lum NFIP requ~reml!nts. ' The co~ity number apd suffix code listed above will be used for all flood insurance policies and renewals issued for your community On and after the effective date listed above. The modifications described herein are effective as of the date of this letter. However, a review of the modifications and any requests for changes should be made within 30 days. Any request for reconsideration muSt be baaed on scientific or technical data. ' This· LOMa will not be printed and distributed to primary lIlap users such as local icsu~anc" age .. ~s and _="~gage, .l.end.ers I. t~er"fpre, the community .. will serve as a reposito~y for these new data. We encourage you to disseminate the information reflected by this LOMa widely throughout the community in order that interested persons such as property owners, insurance agents, and mortgage lenders may benefit from this information. We also encourage you to consider preparing an article for publication in the community's local newspaper that would describe the changes that have been made and the assistance the community will provide in serving as a clearinghouse for these data and interpreting NFIP maps. 1'1 H R 5 ' 3 I 8: 19 FEul'l '91GHT blHTER EII'3IfIEER PHGE • 004 -3 If you have any questions regarding' the modifications described herein, please call the Chief, Natural and Technological Hazards Division, FEHA, in Denver, Colorado, at (303) 235-4830, or Hrs. Cynthia H. Croxdale of my staff in Washington, D.C., at (202) 646-3458. Enclosure '. J:.cL_!'Ir .• "J/ill.iam .L; L.qrah.~ •. ~.E. •.. Vice President, wwE ... <.:..--. -f.'Jft~ Kenneth R. Wrlght, P.E. ~,.-. Chief Engineer, WWE Mr. John L. Blanchard, P.E. Project Engineer, WWE Sincerely, william R. Locke Acting Chief, Risk Studies Division Federal Insurance Administration '. ...... . . . ..... ' ,'. .. , •. -._. ".. _. 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" rZONEA JI ___ =_ .0: ._, '".=" .. '~~~_ -LIMIT OF STUOY .. ",." "",,',o' m. ~'~~y~ --·"~I·~·'==J" =,=I='·=~~=" ~ ... J : liMIT nc ~Tllnv l "~\..1MIT OF STUOV 9 '" ft~, ~IJISeD ZONEC ! /I' LtMIT OF STUDY .-," -.r=_o-,---'=~=Q-E=J -= .-.... ~. .~ ~ I, • -;u In lD (0 lD " ;1) C'· ;:u :; . I -i ~ I· -i m ;1) m GJ ~ m m ;U '1J I> G) m o IS' en ... ~ . •. (-~ -. _.-.... Q .. 'C,",C"J> /..... S"'c..,. 9 • .-.~"'. l'~r' ,\. "-.) ~-. ."~ , ". . /,.. ' . . "." ... . \.. " r j ;., --------.-------------:;:S~:BMI PUD BOUNDAR"......:"'· ,--• D .' FIOURE 2 1888 FIRM \ Dralnag ••• y. ( D 1000 ,o00 -----'CALE. 1M fElT ,------------~----, .. ,. T .............. , ....... "' •• -,-nne "1.'1' .,