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HomeMy WebLinkAbout43 DP Audio Video 05-15 909 University Dr. East. # ' ... FOR OFFICE USE ONLY Case No. 05-f c;; " Date Submitted Crrv OF Coll.EGE STATION Plt11111ing & De11elop 111m1 &>-vices DEVELOPMENT PERMIT ...-. / MINIMUM SUBMITTAL REQUIREMENTS ll.J' _ $200 .00 development permit fee. ~ Drainage and erosion control plan, with supporting Drainage Report two (2) copies each D flf\-. Notice of Intent ( N.0.1.) if disturbed area is greater than 5 acres Site is c:'l'n~ o.sL-o-.cx-es k~. Date of *Required Preapplication Conference: _________________ _ *(Required for areas of special flood hazard) LEGAL DESCRIPTION L..ot-.s 3 !j G..'!)ol 3r=, J3l.o cKst;, LJ...n.\\Jecs\1-g f=>~'6.,1?oo.S? 71 APPLICANT'S INFORMATION (Primary Contact for the Project): Name BrJ-l R iLe £ le.cJri c.. L, E E-Mail K.\J.toisb@. bvce.e.e>. ~ Street Address 300 L D. Lbv''f) Y}) • te Dr . City C 0, , ~ e S.~ ~ J 0V) State Je )f a S Zip C ~de ---'T__,t__.,~'--'4-"5 __ _ PhoneNumber C§J'iitRCJ3 -LJO}lo FaxNumber {9tq) fpCJ 3-9 J5f5 PROPERTY OWNER'S INFORMATION: Name GJ ?o.ct}')t(S LTD E-Mail _________ _ Street Address C) 1J Uf\ive,r s i b1 De £. City to )I ea e s+a + I 0 I) I State lex CtS Zip C~de t 1-'( z 0 Phone Number (g'=lqJ b q {g -51 JC) Fax Number _,_(--=-9t.__q_,_J -=-/p -=-9 -"'-~--'~ 5....__,__f --=-j....LS __ ARCHITECT OR ENGINEER'S INFORMATION: Name c.::£ EV\s ;n e.Rri "'-91-thv irrn~SQJ.1-\ CCMs 11.lranh E-Mail '<'c o nli n.~b?c c.oxn Street Address 3L/O} labor l<ooJ City B ( l/ a (\ State Tu-4 5 Zip Code -------- Phone Nu ~ber (9}9) }}~--Z.)')O Fax Number l9 ~Cf) 1-1-~ -O i.-Z.O Application is hereby made for the following development specific site/waterway alterations: NO'C\ e.. ACKNOW ED~MENTS :l , ~ ~t=:. ('t\ ~ \C~ Co"<\. \~1 '" 1 ' I,_' _,design enginee1 i'I •w, hereby acknowledge or affirm that: 6/13/03 1of 2 -1 ' As a condition of approval of this permit application, I agree to construct the improvements proposed in this application according to these documents and the requirements of Chapter 13 of the College Station City Code Contractor CERTIFICATIONS: A . I, MFC. , certify that any nonresidential structure on or proposed to be on this site as part of this application is designated to prevent damage to the structure or its contents as a result of flooding from the 100-year storm . m .Qil\cA~~~. Engineer Date B . I, .MK, certify that the finished floor elevation of the lowest floor, including any basement, of any residential structure, proposed as part of this application is at or above the base flood elevation established in the latest Federal Insurance Administration Flood Hazard Study and maps, as amended. 04-/14/64- Date C. I, MFC. certify that the alterations or development covered by this permit shall not diminish the flood- carrying capacity of the waterway adjoining or crossing this permitted site and that such alterations or development are consistent with requirements of the City of College Station City Code, Chapter 13 concerning encroachments of floodways and of floodw ays fringes. "1J1 zehl\ ~ 04/14../64- Engineer Date D. I, 1Y\9tw do certify that the proposed alterations do not raise the level of the 100 year flood above elevation established in the latest Federal Insurance Administration Flood Hazard Study. w .~~~~ Engineer 04/14-/04- Date Conditions or comments as part of approval: ------------------------ In accordance with Chapter 13 of the Code of Ordinances of the City of College Station, measures shall be taken to insure that debris from construction , erosion, and sedimentation shall not be deposited in city streets, or existing drainage facilities. All development shall be in accordance with the plans and specifications submitted to and approved by the City Engineer for the above named project. All of the applicable codes and ordinances of the City of College Station shall apply. 6/13/03 2 of 2 CITY O F C OLLEGE STAT ION Planning d-Dnx!Dpmt nt Servicer SITE LEGAL DESCRIPTION: University Park Phase II Lots 3A and 3F of Block V DATE OF ISSUE: April 5, 2005 OWNER: GJ Partners , LTD 911 University Dr. E College Station , TX 77845 TYPE OF DEVELOPMENT: SPECIAL CONDITIONS: DEVELOPMENT PERMIT PERMIT NO. 05-15 FOR AREAS OUTSIDE THE SPECIAL FLOOD HAZARD AREA RE : CHAPTER 13 OF THE COLLEGE STATION CITY CODE SITE ADDRESS: 909 University Dr, CS, TX 77845 DRAINAGE BASIN: Burton Creek VALID FOR 12 MONTHS CONTRACTOR: Full Development Permit Britt Rice Electric , LP 3002 D. Longmire Dr . College Station, TX 77845 All construction must be in compliance with the approved construction plans All trees required to be protected as part of the landscape plan must be completely barricaded in accordance with Section 7 .5.E., Landscape/Streetscape Plan Requirements of the City's Unified Development Ordinance , prior to any operations of this permit. The cleaning of equipment or materials within the drip line of any tree or group of trees that are protected and required to remain is strictly prohibited . The disposal of any waste material such as , but not limited to , paint, oil, solvents , asphalt , concrete , mortar, or other harmful liquids or materials within the drip line of any tree required to remain is also prohibited . The Contractor shall take all necessary precautions to prevent silt and debris from leaving the immediate construction site in accordance w ith the approved erosion control plan as well as the City of College Station Drainage Pol icy and Design Criteria . If it is determined the prescribed erosion control measures are ineffective to retain all sediment onsite , it is the contractors responsibility to implement measures that will meet City , State and Federal requ irements . The Owner and/or Contractor shall assure that all disturbed areas are sodden and establishment of vegetation occurs prior to removal of any silt fenc ing or hay bales used for temporary erosion control. The Owner and/or Contractor shall also insure that any disturbed vegetation be returned to its original condition , placement and state . The Owner and/or Contractor shall be responsible for any damage to adjacent properties, city streets or infrastructure due to heavy machinery and/or equipment as well as erosion , siltation or sedimentation resulting from the permitted work . In accordance w ith Chapter 13 of the Code of Ordinances of the City of College Station , measures shall be taken to insure that debris from construction , erosion , and sedimentation shall not be deposited in city streets , or existing drainage facilities . I hereby grant th is permit for development of an area outside the special flood hazard area . All development shall be in accordance with the plans and specifications submitted to and approved by the City Engineer in the development permit application for the above named project and all of the codes and ordinances of the City of College Station that app ly. Date Date I c '6 c Engmeenng & Environmental Consultants Inc May,2005 Ms. Bridgette George, Development Coordinator City of College Station Development Services 1101 Texas Avenue South P . 0 . Box 9960 College Station, Texas 77842 Re: Third Submittal of Revised Site Plan and Landscape Drawings and Second Submittal of Construction Drawings for Proposed Audio Video Building University Drive near Spring Loop; College Station, Texas Incorporating Revisions in Response to Staff Review Comments No. I Case File #05-041 Dear Ms . George : This letter transmits the revised site development documents outlined in your Memorandum dated April 22 , 2005 for the proposed Audio Video Building planned to be located on the northern side of University Drive East, west of the intersection with Spring Loop in College Station, Texas . The submitted site development documents include the following three (3) separate items: ( 1) Nine (9) complete sets of the site construction plans prepared by CSC and including the attached copies of the revised site plan and landscape plan (six (6) "public" copies of the plans for the City of College Station and three (3) "private" copies of the plans for the contractor, owner/developer, and site engineer); and (2) two copies of the revised site plan as prepared by CSC Engineering & Environmental Consultants, Inc . and labeled as SP-I ; and (3) one copy of the revised landscape plan as prepared by the Land Design Group , Inc . and labeled as L-1 . A listing of the individual construction drawings is presented in the accompanying Table 1 The submitted site plan, landscape plan, and construction drawings have all been revised to address the comments of the City of College Station staff as outlined in the previously referenced Memorandum . The presently submitted construction documents also reflect the changes discussed for the site plan and the landscape plan. More specifically, an erosion protection detail for the existing stormwater inlets has been added to Sheet C-7 . With respect to the second comment, Sheet C-2, which is entitled Site Plan , is included with the construction drawing set but it is intended to be less detailed that the single sheet site plan labeled as Sheet SP-I which is submitted to the City for code and regulatory compliance review . For example, Sheet SP-I will contain parking space calculations which do not need to be on the contractor 's site plan. Therefore, Sheet C-2 is not intended to replace Sheet SP-I, but merely to be a pared down version of the site plan with only the basic information needed for provided an overall view of the scope of construction . Details indicated on Sheet SP-1 .1, such as paving sections , do not need to be repeated on Sheet C-2 since such details are located on other sheets of the construction plans. 3407 Tabor Road Bryan, Texas 77808 Phone (979) 778-2810 Fax (979) 778-0820 .. -Re-submittal of Revised Site and Landscape Plans and Submittal of Construction Documents Submittal No . 2 Based Upon Staff Review Comments No . I Proposed Audio Video Building; College Station, Texas Page2 The only item mentioned in the referenced Memorandum that is not included in this submittal is "One ( 1) revised grading plan." The staff comments listed in the referenced Memorandum did not include any comments on grading . There is a grading sheet in the set of construct ion drawings and telephone conversations with Mr. Josh Norton indicated that this sheet would be acceptable for review . Table 1. Listing of the Submitted Site Development Const ruction Drawings for the Proposed Audio Video Building; College Station, Texas SHEET DRAWING REVISON DATE NO. TIT L E NO . CONSTRUCTI O N DRAWINGS Cover Sheet C-1 General Notes 0 05/02/05 C-2 Site Plan and Utility Plan 0 05/02/05 C-3 Dimension Control P lan 0 05102105 C-4 Grading and Drainage Plan 0 05/02/05 C-5 P aving and Paving Detail s 0 05/02/05 C-6 Details 0 05102105 C-7 Erosion Control Plan 0 05/02/05 SP-1.1 Architectural Site Plan 0 January 2005 • s Joint Standard Waste Water Details 0 Undated w Joint Standard Water Details 0 Undated ADDITIO NAL DRAWING SUBMITTALS SP-1 Site Plan (corrected second submission) 0 04/29/.05 L -1 Landscape Plan (corrected second submission) 0 April 2005 NOTES: a. Drawing signed on 04/1 2 .05 We sincerely appreciate your assistance in facilitating this submittal . Please do not hesitate to call should any questions arise or if additional information is required. Kindest regards , CSC Engineering & Environmental Consultants, Inc. /_.-L-4- M . Frederick Conlin, Jr. P .E ., JD Senior Engineer MFC :am via: Hand Delivery Attachments : (Listed in Body of Letter) Andres Almanza Designer CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. CITY OF COLLEGE STATION Plann ing & Devewpmmt Services SITE LEGAL DESCRIPTION: University Park Phase II Lots 3A and 3F of Block V DATE OF ISSUE: April 15, 2005 OWNER: GJ Partners , LTD 911 University Dr. E College Station , TX 77845 DEVELOPMENT PERMIT PERMIT NO . 05-15 Project Description FOR AREAS Outside THE SPECIAL FLOOD HAZARD AREA RE : CHAPTER 13 OF THE COLLEGE STATION CITY CODE SITE ADDRESS: 909 University Dr, CS, TX 77845 DRAINAGE BASIN: Burton Creek VALID FOR 6 MONTHS CONTRACTOR: Britt Rice Electric, LP 3002 D. Longmire Dr. College Station , TX 77845 TYPE OF DEVELOPMENT: Clearing and Grading Only SPECIAL CONDITIONS: All construction must be in compliance with the approved construction plans Clearing and Grading Permit Only The Contractor shall take all necessary precautions to prevent silt and debris from leaving the immediate construction site in accordance with the approved erosion control plan as well as the City of College Station Drainage Policy and Design Criteria . If it is determined the prescribed erosion control measures are ineffective to retain all sediment onsite, it is the contractors responsibility to implement measures that will meet City , State and Federal requirements. The Owner and/or Contractor shall assure that all disturbed areas are sodden and establishment of vegetation occurs prior to removal of any silt fencing or hay bales used for temporary erosion control. The Owner and/or Contractor shall also insure that any disturbed vegetation be returned to its original condition, placement and state . The Owner and/or Contractor shall be responsible for any damage to adjacent properties, city streets or infrastructure due to heavy machinery and/or equipment as well as erosion, siltation or sedimentation resulting from the permitted work . Any trees requ ired to be protected by ordinance or as part of the landscape plan must be completely fenced before any operations of this permit can begin . In accordance with Chapter 13 of the Code of Ordinances of the City of College Station, measures shall be taken to insure that debris from construction , erosion , and sedimentation shall not be deposited in city streets , or existing drainage facilities . I hereby grant this permit for development of an area Outside the special flood hazard area . All development shall be in accordance with the plans and specifications submitted to and approved by the City Engineer in the development permit application for the above named project and all of the codes and ordinances of the City of College tio that apply . p:\group\htltr\pzltr\prod\pz2005 \p0011025 .doc Engmeenng & Environmental Consultants, Inc. 4-/4--05 00-/F) April 13 , 2005 Ms . Bridgette George, Development Coordinator City of College Station Development Services 1101 Texas Avenue South P . 0 . Box 9960 College Station, Texas 77842 Re: Second Submittal of Revised Site Plan and Landscape Drawings and First Submittal of Construction Drawings for Proposed Audio Video Building University Drive near Spring Loop ; College Station, Texas Incorporating Revisions in Response to Staff Review Comments No. 1 Case File #05-041 Dear Ms . George : This letter transmits the revised site development documents outlined in your Memorandum dated April 1, 2005 for the proposed Audio Video Building planned to be located on the northern side of University Drive East, west of the intersection with Spring Loop in College Station, Texas . The submitted site development documents include the following four (4) separate items : (1) the revised site plan as prepared by CSC Engineering & Environmental Consultants , Inc . and labeled as SP-1 ; (2) the revised landscape plan as prepared by the Land Design Group, Inc. and labeled as L- 1; (3) one complete set of the site development construction documents prepared by CSC and including the attached copies of the previously cited revised site plan and landscape plan; and (4) a drainage report . A listing of the individual construction drawings is presented in the accompanying Table l The submitted site plan, landscape plan, and construction drawings have all been revised to address the comments of the City of College Station staff as outlined in the previously referenced Memorandum . The presently submitted construction documents also reflect the changes discussed for the site plan and the landscape plan . Also transmitted via this letter is a $200 check for the Development Permit. 1fS 3 :"34 3407 Tabor Road Bryan , Texas 77808 Phone (979) 778-2810 Fax (979) 778-0820 Re-submittal of Revised Site and Landscape Plans and Submittal of Construction Documents Submittal No. 2 Based Upon Staff Review Comments No. l Proposed Audio Video Building; College Station, Texas Page2 Table 1. Listing of the Submitted Site Development Construction Drawings for the Proposed Audio Video Building; College Station, Texas SHEET DRAWING REVISON DATE NO. TITLE NO. CONSTRUCTION DRAWINGS Cover Sheet C-1 General Notes 0 4/11/05 ,_ C-2 Site Plan and Utility Plan 0 4/11/05 C-3 Dimension Control Plan 0 4/11/05 C-4 Grading and Drainage Plan 0 4/11/05 C-5 Paving and Paving Details 0 4/11/05 C-6 Details 0 4/11/05 C-7 Erosion Control Plan 0 4/11/05 SP-1.1 Architectural Site Plan 0 January 20053 s Joint Standard Waste Water Details 0 Undated w Joint Standard Water Details 0 Undated ADDITIONAL DRAWING SUBMITTALS SP-I Site Plan (corrected original submission) 0 04/11.05 L-1 Landscape Plan (corrected original submission) 0 NOTES: a . Drawing signed on 04112.05 We sincerely appreciate your assistance in facilitating this submittal . Please do not hesitate to call should any questions arise or if additional information is required . Kindest regards , CSC Engineering & Environmental Consultants, Inc. m.~~~- M. Frederick Conlin, Jr. P .E ., JD Senior Engineer MFC :am via: Hand Delivery Attachments: (Listed in Body of Letter) Andres Almanza Designer CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Andres Almanza From: To: Sent: Attach: Subject: "Jeffrey Speed" <Jspeed@cstx .gov> <aalmanza@txcyber.com> Monday , April 11 , 2005 3 :30 PM UniversityPark2_ 1 O_Replat.pdf Re : Audio Video I don't show that easement to exist any more based on the attached replat from 2003. Page I of I 4/11/2005 ~ ,,,... \ \ ~ \ ... \~ \ ~ ' DRAINAGE REPORT FOR PROPOSED AUDIO VIDEO BUILDING UNIVERSITY DRIVE NEAR SPRING LOOP COLLEGE STATION, TEXAS Prepared for Britt Rice 3002 Longmire Drive Suite D College Station, TX 77845 Submitted to City of College Station Development Services 1101 Texas Avenue College Station, Texas 77842 Prepared by CSC Engineering & Environmental Consultants, Inc. 3407 Tabor Road Bryan, Texas 77808 April 2005 1!1.~e~~ M. Frederick Conlin, P.E. Senior Engineer CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. TABLE OF CONTENTS Page 1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT .............................. 1 2.0 DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT .................................................. 1 2.1 SITE LOCATION ................................................................................................................. 1 2.2 EXISTING SITE CONDITIONS ......................................................................................... .2 2.3 PROPOSED SITE DEVELOPMENT SCHEME .................................................................. 2 3.0 LOCATION OF THE SITE WITHIN THE MAJOR DRAINAGE BASIN AND EXISTING DRAINAGE PATTERNS IN THE AREA OF THE SUBJECT SITE ....................... .3 4.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA .................................................... 3 5 .0 STORM WATER RUNOFF COMPUTATIONS .......................................................................... .4 5.1 USE OF THE RATIONAL FORMULA .............................................................................. .4 5.2 RUNOFF COEFFICIENTS (C) ............................................................................................ 5 5.3 TIME OF CONCENTRATION (Tc) ..................................................................................... 6 5.4 RAINFALL INTENSITY (1) ................................................................................................. 7 5 .5 AREA OF SITE (A) .............................................................................................................. 7 5.6 STORM WATER RUNOFF QUANTITIES ......................................................................... 7 6.0 STORM WATER DETENTION .................................................................................................... 9 6.1 REQUIRED MINIMUM DETENTION STORAGE VOLUME .......................................... 9 6 .2 DETENTION BASIN STORAGE AREA ............................................................................ 10 6 .3 DETENTION BASIN OUTLET STRUCTURE ................................................................... 10 7 .0 EROSION CONTROL MEASURES ............................................................................................. 12 7.1 GENERAL CONSIDERATIONS ......................................................................................... 12 8.0 CERTIFICATION ........................................................................................................................... 12 9.0 REFERENCES ................................................................................................................................ 13 LIST OFT ABLES Table 1. Summary of Determination of Runoff Coefficient (C) Values for Post-Development Conditions for Entire Site ...................................................................................................... 6 Table 2. Computed Rainfall Intensity Values for Defined Storm Return Period ................................ 7 Table 3. Calculation of Pre-and Post-Development Storm Water Runoff Quantities Using the Rational Method .................................................................................................................... 8 .. ,. 11 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. ~~,-~---~-~ ... o/.:.~~~-~~~~--------·---·---·-·--. ~--··-------· ---~~a,;;_ ~:.£?.~~p r ~~~.2,L _, ·-·--· --"-·~~-·~•~"----~-w--.~~~d_~':~?!!Buil~~~~~~.tat ~~~ 1?' Figure 1. Figure 2 . Figure 3 . Figure 4 . Figure 5 . Figure 6. Figure 7 . Figure 8. LIST OF FIGURES Vicinity Map Burton Creek Drainage Basin Aerial Photograph (2002) of Subject Site and Surrounding Area Pre-Development Site Conditions and Stormwater Runoff Flow Patterns FIRM Flood Plain Map of Area of Subject Property Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns Types of Ground Cover Associated With Post-Development Scheme Pre- and Post-Development Unit Hydrographs for 100-Y ear Storm Event Ill CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. i:Mm @,.,. -~~~-·-·--~~-£"iiil_• ______ -·iri --•••m-•-,,~--... ~:£0!!: o fE~in ~:_.stu~.. n· -·~·--·-"' • ~ _ ·~ ··~ ~ • Pro P?,sed ~~~~~?.~ei. <;~1!:.e~ s;~tio~'... T_x 1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT This report documents the information used in the formulation of the stormwater drainage system for the proposed Audio Video Building development being constructed by Britt Rice Electric, L.P . (BRE) in College Station , Texas. 2.0 DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT Information concerning the project was provided by Mr. Kenny Walsh , Project Manager with BRE, the general contractor for the project, and by Mr. Brett Cumpton, AIA , with the project architects, Cumpton & Associates . 2.1 SITE LOCATION The property which is the subject of the proposed development and this drainage report is situated on the northern side of University Drive East, approximately 1,500 to 1,600 ft west of the intersection with Spring Loop (see Figure 1 -Vicinity Map in Appendix A ; all figures referenced in the report are in Appendix A). The site is situated within the Burton Creek Drainage Basin (Figure 2 -Burton Cree k Drainage Basin). As can be seen from a review of Figure 3 -Aerial Photograph (2202) of Subject Site , existing commercial developments border the subject property to the south (David Gardener 's Jewelers), west (Buffalo Wild Wings restaurant), east (office park), and north (Comfort Suites Hotel (currently under construction)). The proposed office building will be situated on an undeveloped lot that is referred to as Lot 3R of Block V of the University Park Addition -Phase II. The subject site is located immediately behind Lot 3A of the referenced subdivision. Lot 3A is currently occupied by the David Gardener 's Jewelers building that has a physical address of 911 University Drive East. ! .. ·• 't"-" .•• - CSC ENGINEERING & ENVIRONMENT AL CONSULT ANTS, INC. !f~'<;. ,..,, '"L ~~ ..... ~,;j1>_, Report of Drainage Study Proposed Audio Video Building; College Station, TX ..,, '""..,._ ~" , ... _.,,.,.,... .... ·~ . .,, ·.-·~· .... ·---........ ,,.~-.,_ .... 2.2 EXISTING SITE CONDITIONS The subje ~) extends over an area of approximately 0.53-acre and is undeveloped , being covered by sho /gasses1and a few isolated trees as indicated in the aerial photograph in Figure 3. The subject site has a pronounced slope in a northerly direction toward the adjacent Comfort Suites Hotel site . The predominant direction of stormwater surface runoff flows follows the surface grade toward the hotel site as illustrated in Figure 4 -Pre-Development Site Conditions and Storm Water Runoff Flow Patterns. Surface grades vary across the site from approximately 2. 7 to 5 percent, but average approximately 3 percent. Burton Creek is situated approximately 2,500 ft to the north of the project site and north of Spring Loop and Autumn Circle (Figure 1) In addition, there is a small, unnamed tributary drainage swale approximately 500 ft west of the subject site that flows in a northerly direction to Burton Creek (Figures 1, 2 and 3). The proposed site is not located within any existing flood plains as illustrated on Figure 5, FIRM Flood Plain Map of Area of Subject Property. 2.3 PROPOSED SITE DEVELOPMENT SCHEME The proposed development will consist of a single-story office/retail building of approximately 8, 115 square feet in area and associated paved driveway and parking areas of approximately 4,978 square feet in area as illustrated on Figure 6 -Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns . CSC anticipates that the proposed office building structure will be situated in the southwestern portion of the previously described property as illustrated in Figure 6 . We also anticipate that the proposed office building will have a single sloped roof that slopes to the north. We further anticipate that the proposed paved area will be located east of the proposed building (Figure 6) and will provide access to a drive-in bay of the building, as well as provide parking spaces for approximately eight vehicles. Additional parking will be provided by "off-site" paved areas on the adjacent lot (Lot 3A) that is currently occupied by David Gardener's Jewelers . We anticipate that the paved drive and parking areas associated with the new building will be constructed of a rigid pavement system with a Portland cement concrete (PCC) surface. Landscaping of the site will be established in the areas immediately around the office building and in the islands and areas bordering the paved access drive and parking area. 2 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. "' .... ~ Pr~~!:.~. Aud!? Vide:> ~~~~in~;--~~o ~~~_:_S ~tion, TX The finished floor slab elevation of the building will be at approximately El. 319 .5. The finished floor elevation will require some small volumes of fill to be added to the southern portion of the site in order to achieve final grades in the building pad area. Greater thicknesses of fill will be required in the northern area of the site. We anticipate that the fill heights will vary from 0 .5 ft in the southern portion of the building pad to approximately 4 feet in the northern portion of the pad. Finally, we do not anticipate that the building will have a basement or a storm shelter or other features that would require structural excavations at the site. 3.0 LOCATION OF THE SITE WITHIN THE MAJOR DRAINAGE BASIN AND EXISTING DRAINAGE PATTERNS IN THE AREA OF THE SUBJECT SITE As previously discussed , the subject 0 .53-acre site is located in the middle reaches or middle portion of the Burton Creek drainage basin (Figures I and 2). The subject site is located approximately 2,500 feet south of the Burton Creek channel. The subject site is situated at a point within the drainage basin that is approximately 3 ,400 feet downstream of the junction of Tributary C of Burton Creek and the main channel of Burton Creek, and approximately 3,600 feet upstream from the point where Burton Creek flows into Carters Creek (see Figure 1). There are no distinct drainage channels across the existing site . The major portion of current storm water runoff from the site appears to be by sheet-flow in a northerly direction toward the adjacent hotel site. The stormwater runoff previously flowed across the hotel site to various pavement sections along Spring Loop or private roadways adjacent to Spring Loop where the collected storm water runoff was routed via street gutters to existing storm sewer curb inlets . The storm water collected in the curb inlets was then discharged through a system of storm sewer pipes into Burton Creek, which , as previously mentioned, is situated north of the subject property. 4.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA This report described the planned storm water drainage system for the proposed development and addresses the volume of storm water detention required following the planned development of the building and associated paved areas. Both the site and the proposed development scheme were evaluated 3 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. ~~~~~·""'" .. ~..tt ...,..""" -,.,;7 ,,.:"'-~:.;;.."'1t~<<f•ei, :~.:n~~ ...... -...... t -·1,1 i#.u•1::t1~A~~ ... "' in accordance with the criteria outlined in the "Drainage Policy and Design Standards (DPDS)" manual of the City of College Station, Texas. The DPDS manual is undated but contains a chapter on "Flood Hazard Protection" that has a revision date of October 1, 1990 . This report also discusses general erosion control measures. 5.0 STORM WATER RUNOFF COMPUTATIONS 5.1 USE OF THE RATIONAL FORMULA The Rational Formula was used to compute the volume of storm water runoff prior to and following the planned development. Calculations based upon the Rational Formula were employed to ::> assess the quantity of storm water that must be detained to "~ffset" the increased runoff associated with 'the new development. The generalized grading of the site and the general direction of pre-development flow are illustrated on the accompanying Figure 4 . The proposed grading plan for the development and the patterns of post-development storm water runoff flows are illustrated on the accompanying Figure 6 . Use of the Rational Formula is reasonable for this project since the contributory area of runoff is less than 50 acres, an area sometimes referenced in the literature as an upper limit for use of the Rational Formula. In addition , the subject site is located within a Secondary Drainage System and not within a Primary Drainage System . The Rational Formula is not recommended for use within a Primary Drainage System . Therefore, the Rational Formula was used to determine the peak discharge for both pre-and post- development conditions . The general equation for the Rational Formula is well known: Q=CIA where Q = discharge of storm water in units of cubic feet per second ( cfs) C = coefficient that represents the average runoff characteristics of the land cover within the drainage area of interest, i.e ., the runoff coefficient, which is dimensionless I= rainfall intensity in units of inches per hour (in/hr), and A = area of the site that contributes to the storm water runoff in units of acres 4 .< '.~ -··.""~~.--,.:~. I ,.:..-.) ._ .....- CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX • __ .... , --~ ... --.-..,,,,_ • -< -·""'' . --·-'~..--· ,..,,._ ., . ·-" ~ . ~-· .,.,.. ,.,, ~ - The values of each of the factors contained in the equation that were employed to compute the storm water runoff at the subject site are discussed in the following sections . 5.2 RUNOFF COEFFICIENTS (C) The runoff coefficients or "C" values were computed for both pre-and post-development conditions. Coefficients for the different types of surface covers were determined from Table III -1 of the DP DS manual. The coefficient for the pre-development condition was determined based upon the land cover category listed in Table III-1 as a combination of "Natural Woodlands " and "Natural Grasslands " for slopes in the range of 1 % to 3 .5%. A range of C-values of 0.18 to 0 .25 is listed in the referenced table for the "Natural Woodlands " and a range of C-values of 0.35 to 0.45 was given for ''Natural Grasslands" for the cited topographic conditions. Accordingly, an average value of 0.4 was selected for use for pre- development cover of the entire 0.53-acre site. An average C-value for post-development conditions was also calculated . The post-development C-values were determined from the referenced table in the DPDS for the specific types of site cover associated with post-developed site conditions . An illustration of the various types of site cover anticipated for post-development conditions is presented in Figure 7 -Types of Ground Cover Ass ociated With Post-Development Scheme . The specific types of post-development cover materials illustrated in Figure 7, the corresponding C-values from Table III-I of the DPDS manual, and the approx imate areas of the various types of cover materials listed in Figure 7 were used in the analysis outlined in Table 1 of this report to compute an average C-value for the post-developed site. In general, a unit C-value of 0.9 was used for building roof and concrete covered pavements and sidewalks and a unit C-value of 0 .5 was used for the landscaped or grassed areas as indicated in Table 1. Therefore , the average C-value for the post-developed site can be determined by dividing the summation of the product of the individual areas times the respective unit C-values listed in Table I and dividing that summation by the overall site area which is also listed in Table 1. The result of that calculation is as follows: Average C-value = summation of unit C-values times individual areas divided by the total site area Average C-value = 17 ,184 C-square feet I 23,894 square feet = 0.71 5 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC . .;,;ar . ; ':IQ -~~~i_,.;a:: ,Q '*11• >J;..".a~~~oiiUU.. • 7J"'i:~&:t:,..,.,..,,,,,..,,,..,, t; _ m , • !'!?.£?,se,d. ~,~~~ .:'!d ~_?-~uH~~g ; Co ll ~~C:~~-tation , TX Table I . Summary of Determination of Runoff Coefficient (C) Values for Post-Development Conditions for Entire Site Area of Area of Typical Extended Multiplication Type of Ground Cover Coverage, Coverage, C-Values of square feet Acres C-Values time Area, sq ft Concrete (sidewalks , streets, etc .) 4,978 0.11 0.90 4,480 Building roof 8,115 0.17 0.90 7,304 Grassed or landscaped areas 10 ,801 0.25 0.50 5,400 Summation 23,894 0.53 17,184 5.3 TIME OF CONCENTRATION (Tc) The time of concentration at a site is used to determine the intensity of the rainfall event used for computing storm water flows and required detention volumes. The time of concentration is defined as "the time required for the runoff to be established and flow from the most remote part of the drainage area to the point under design." For pre-development conditions the time of concentration for the subject site was calculated based upon the elevation difference and the flow distance from the higher elevations in the southern portion of the property to the lower elevations is the northern portions of the site adjacent to the hotel site to the north The referenced change in elevation is 4 ft and the referenced distance is approximately 220 ft. This grade produces a slope of approximately 2% for pre-development conditions . The slope for post-development conditions was determined from the proposed site grading plan and drainage patterns as illustrated in Figure 6. The surface slopes or grades and the velocities presented in Table III-2 of the DPDS manual were used to determine the appropriate storm water runoff velocity . For overland or sheet-flow over slopes in the range of 0 to 3 percent, such as are present at the subject site , velocities of runoff flow are listed to be in the range of 0 to 1.5 feet per second (fps) for natural woodlands and in the range of 0 to 2.5 fps for natural grasslands . An average velocity of 2 fp s was conservatively selected for pre-development conditions. Thus, time of travel between the location of the higher elevations of the site and the lower elevations of the site was calculated to be approximately 110 seconds (220 ft distance/2 fps velocity) or approximately 1.8 minutes for pre-development conditions . The post-development time of concentration was calculated over the paved areas of the site without consideration of any detention and was determined to be a shorter time period. Therefore, a minimum time of concentration of 10 minutes (as specified in the DPDS manual) was used in the calculations for both pre-and po st-development conditions. 6 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. ..,.~ """' -..-.. .• JY £;~~~ --~:--.. ---··a.-rF -··mi-----.. ·;..---. w ~:P.?.~ .. ?.f ~~~. ~--~·~,-Proposed Audio Video Buildin g; Coll ege Station, TX -~··-;;A<~ .. ..,,.,.._ ....... ._. ...... -..... ---.3'--~-..._ _____ .... ..-.~..... .. - 5.4 RAINFALL INTENSITY (I) The rainfall intensity values were computed for the minimum 10 -minute time of concentration previously discussed using the intensity-duration-frequency curves developed by the Texas Department of Transportation. The computed intensities calculated for storm events with "return periods" of 5, 10 , 25, 50 , and 100 years are indicated in Table 2. Table 2. Computed Rainfall Intensity Values for Defined Storm Return Period Storm Return Period (Years) 5.5 AREA OF SITE (A) 5 10 25 50 100 Rainfall Intensity (Inches/Hour) 7.7 8.6 9.9 11.1 12.3 The area of the site used in the computation of storm water runoff is the original site area of 0.53 acres as indicated on Figures 4 and 6 . 5.6 STORM WATER RUNOFF QUANTITIES Storm water runoff quantities were calculated using the Rational Formula. Runoff quantities were calculated for both pre-and post-development conditions for the 0.53 -acre site for storm events with recurrence intervals of 5, 10 , 25 , 50 and 100 years . The rainfall intensities used in the computations were as discussed in Section 5.4 . The results of the computations are presented in Table 3. 7 - CSC E NGINEERING & ENVIRONM ENT AL C O NSULTANTS, INC. Table3. Calculation of Pre-an d Post-Develo pment Storm W ater Ru noff Q uantities Using the Rational Method PRE-POST-DIFFERENCE Storm Area. Intensityc DEVELOPMENT DEVELOPMENT IN F L OWS Event (ac res) (inches (year) /hr) Cp,./ Qp re Cpost • Q post Q o dless ~fs dless (cfs) (cfs) 5 0 .53 7 .7 0 .4 0 1.63 0 .7 1 2.9 0 1.27 10 0 .53 8.6 0 .4 0 1.82 0 .71 3.24 1.42 25 0.53 9 .9 0 .4 0 2 .10 0.7 1 3 .73 1.63 50 0 .53 11.1 0.40 2.3 5 0 .7 1 4.1 8 1.83 100 0 .53 12.3 0 .4 0 2.6 1 0 .7 1 4.6 3 2 .0 2 •Average values ofC were obtained from Table III-I of the DPDS Manual b dless =dimensionless c Values obtained from Table 2 of this report 8 •. J ' · .. t,·-:). ''<• ,,; ·t • .,.., CSC ENGINEERING & ENVffiONMENTAL CONSULTANTS, INC. 6.0 STORM WATER DETENTION 6.1 REQumED MINIMUM DETENTION STORAGE VOLUME CSC has noted that the proposed site is relatively small and occupies an area of only 0 .53-acres . In addition, a significant portion of the site will remain as landscaped areas following development. As can be seen from a review of Table 2, approximately 47 percent of the site will still be landscaped. Therefore, the difference in pre-and post-development flows for any storm recurrence interval will be relatively small. The storage volume of the detention area was calculated such that the peak discharge of the ultimate development hydrographs for the 100-year design storm was limited to a discharge less than a defined target discharge. The defined target discharge was characterized by the DPDS manual to be the peak discharge of the pre-development hydrograph for the 100-year storm event. Since the entire 0.53- acre site is being developed at the present time, the current developed condition and the ultimate developed condition were assumed to be the same. The required detention storage volume was determined as the difference in area between the pre- and post-development hydrographs, as depicted on Figure 8 The Triangular Approximation method was used to determine the hydrographs. The hydrographs were constructed by assuming that the peak discharge, as calculated from the Rational Formula, occurs at a time equal to the time of concentration and that one-third of the flow volume occurs before the peak discharge is reached and two-thirds occur following the peak discharge. The Triangular Approximation method of developing hydrographs is generally considered to be acceptable for analysis of Secondary Drainage Systems with an area of less than 50 acres, which is applicable to the drainage basin addressed in this report. The difference in area between the two hydrographs , or the required minimum volume of the detention storage area, was calculated to be approximately 1,818 cubic feet for the 100-year recurrence interval storm event. 9 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. l!M..,~~~ IC w~J:e 41·"-~~ _,.1 'Hf .~~'.Nl'r~~~~~,a_ ... _ -i.i~--~~~~~ r'a;a!R.~l'\--.;..~.'Q"A:. :It'•~-. ~:i'~rt o~ ~~ain ~~~ ~tu ?y . . Pr~~~;d A~dio .Yi<l,:.o Bui ~dingi ~ol ~J~~ Stat ~?n, TX 6.2 DETENTION BASIN STORAGE AREA We propose to provide the required detention storage within the planned paved area on the eastern side of the proposed building, which is indicated by the blue shading on Figure 6. The required volume for storm water detention will be created by depressing the pavement surface and the corresponding top of the storm water catch basin inlet within the paved area to an elevation that is below the surrounding perimeter curb elevations and also below the high break points in the pavement grading . The proposed detention area will have a square to rectangular shape as depicted on Figure 6 and will have approximate plan dimensions of 64 feet by 80 feet with some interior parking islands excluded. The area of the stormwater detention basin was determined to be approximate 4,376 square feet (sq ft). The stormwater inlet box at the approximate center of the detention basis will serve as the outlet for the captured storm water is discussed in greater detail in the following section of this report. The elevation of the top of the storm water inlet box was established at approximately 10 inches or 0.83 feet below the elevation of the high break point in the pavement grade to the south of the inlet box and well below the top elevation of the curbs surrounding the detention area. Therefore, approximately 10 inches or 0.83 feet of water could pond at the inlet location . The depth of ponded water is expected to vary from I 0 inches at the inlet location to 0 inches at the curb and high break point locations, with an average depth of approximately 5 inches or 0.42 feet over the entire area. The maximum depth of ponding of 10 inches r--- or 0.83 feet is permitted for parking areas used as detention basins according to the DPDS (page 74). No higher elevations of ponding are possible since an overflow of the high break point in the paving would occur for ponded depths above l 0 inches , and the stormwater would flow to the adjacent paved area of the existing storm water catch basins in the David Gardener's Jewelers parking lot. The approximate volume provided by the proposed detention basin was computed by multiplying the area of the detention basin ( 4,376 sq ft) by an average ponded water depth of 5 inches (0.42 ft). The computed detained volume was approximately 1,838 cubic feet (cu ft). As previously stated , the required minimum storage volume of the detention basin would be approximately 1,818 cu ft in order to detain the difference between the I 00-year event storm water runoff for pre-and post-development conditions. The minimum required volume of 1,818 cu ft is within the available storage capacity of the proposed detention basin . 6.3 DETENTION BASIN OUTLET STRUCTURE As previously indicated, the outlet structure for the detention basin will consist of the grated inlet that will be constructed in the proposed paved area east of the proposed building. The grate across the top 10 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. of the box will be chosen so that it will pass a flow that is approximately equal to the maximum pre- development flow of 2 .61 cfs for the 100-year storm recurrence interval. The flow through the grate will be calculated based upon a maximum depth of ponded water of 10 inches (0.42 feet). The flow capacity of any inlet grate in a sump or ponded condition is a function of both the depth of water over the grate and the total clear opening area of the grade . The flow can generally be determined by the following equation : Q =CA (.../(2 gd)) where Q = flow rate through the grate inlet in cfs C =orifice coefficient,::::: 0.67 for grate inlets, dimensionless A = clear opening of grate , square inches g =acceleration constant of gravity, ::::: 32.2 feet per square second (ft/sec2) or 2.683 inches per square second (in/sec2) d = depth of water over grate , feet The equation can be simplified to ... Q = 0.0108 A (.../d) where Q = flow rate through the grate inlet in cfs A = clear opening of grate, square inches ::::: 32 .2 feet per square second (ft/sec2) or 2.683 inches per square second (in/sec2) d = depth of water over grate, feet The referenced equation is generally valid for inlet grates in a sump condition wh ere water depths are 4 inches are greater. At water depths less than 4 inches the inlet grate acts as a weir to incoming flow and requires different analysis to determine flow capacity . Substituting the desired flow of 2.61 cfs and the l 0 inch depth of water over the grate inches, the approximate open area of the grate that is required can be determined as follows : Q = 0 .0108 A (.../d) 11 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. 2 .61cfs =0.0108 A (.../10 inches) or ... A= (2 .61 cfs) I [0.0108 x .../10 inches]= 2 .61 cfs/0 .03 solving ... A = 76.4 square inches The catch basin designated by East Jordan Iron Works, Inc . as model or catalog number V-5714 has an opening of 75 square inches, which is approximately equal to the required opening area of 76.4 square inches . The referenced grate inlet or its equivalent has been specified on the construction drawings for the referenced grated box inlet. 7.0 EROSION CONTROL MEASURES 7.1 GENERAL CONSIDERATIONS The erosion control measures proposed at the site will basically consist of silt fences that are placed on the three (3) down-gradient boundaries of the site . We do not anticipate the need for hay bale barriers , rock dam s or sedimentation traps since there will not be any channelized or concentrated flows produced by the construction operations . The locations and detailing of the proposed erosion control measures are depicted on Sheet C-7 of the submitted construction plans . 8.0 CERTIFICATION "I hereby certify that this drainage report for the 0.53-acre site that is referred to as Lot 3R of Block V o f the University Park Addition -Phase II and which is the site of the proposed Audio Video Building in College Station, Texas, was prepared under my supervision in accordance with the previsions of the City of College Station "Drainage Policy and Design Standards (1990)" for the owners thereof." 7nl~em11~ M. Frederick Conlin, Jr., P .E. Registered Professional Engineer State of Texas P.E . Number 44481 12 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. .~tt~·· 9.0 REFERENCES Chow, Ven T., Maidment, David R., and Mays, Larry W. 1988. Applied Hydrology. McGraw-Hill Book Company. New York, NY. 1988 . City of College Station, Texas. 1990. "Drainage Policy and Design Standards," part of the Stormwater Management Plan for the City of College Station. October, 1, 1990. Davis, Victor D., and Sorensen, Kenneth E. 1969. Handbook of Applied Hydraulics . McGraw-Hill Book Company. New York, NY. 1969. Federal Emergency Management Agency. Flood Insurance Rate Map; Brazos County Texas and Incorporated Areas; Panel 142 of250. FIRM Map Number 48041C0142 C, Effective Date: July 2, 1992. Hann, C. T., Barfield, B. J., and Hayes, C. J . 1994 . Design Hydrology and Sedimentology for Small Catchments. Academic Press, Inc. San Diego, CA. 1994. Mason, John M. and Rhombrerg, Edward L. 1980. On-Site Detention . Prepared for Texas Engineering Extension Service, Texas A& M University. College Station, TX. 1980. Publication No. PWP: 03355-01. McCuen, Richard H. A Guide to Hydrologic Analysis Using SCS Methods . Prentice-Hall, Inc. Englewood Cliffs, NJ. 1982 . United States Department of Agriculture. 1975. Urban Hydrology for Small Watersheds. Technical Release No. 55. Engineering Division, Soils Conservation Service, U.S. Department of Agriculture . January 1975. Wanielista, Martin P. 1978. Stormwater Management Quantity and Quality. Ann Arbor Science. Ann Arbor, MI. 1978. Westaway, C.R. and Loomis, A. W . 1979 . Cameron Hydraulic Data. (16th Edition). Ingersoll-Rand . Woodcliff Lake, NJ. 1979. 13 Figure 1. Figure 2. Figure 3 . Figure 4 . Figure 5 . Figure 6. Figure 7. Figure 8. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC .. FIGURES Vicinity Map Burton Creek Drainage Basin Aerial Photograph (2002) of Subject Site and Surrounding Area Pre-Development Site Conditions and Stormwater Runoff Flow Patterns FIRM Flood Plain Map of Area of Subject Property Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns Types of Ground Cover Associated With Post-Development Scheme Pre-and Post-Development Unit Hydrographs For 100-Year Storm Event c s c I L ng111cc1111g & L 11r11 011mcmal Cu11wltallls. l lll BRITI RICE ELECTRIC . LP ! I VICINITY MAP AUDIO VIDEO COLLEGE STATION , TEXAS PROJECT: Audio Video LOCATION : Colle e Station , TX APPR: MFC REV . DATE: DRAWN BY: AEA SCALE : AS SHOWN DATE: 04/11/05 FIGURE NO .: 1 UN I VERS I TY DR . ' ' I / J ' \ ' \ I c s c F.M. ~ 0 .,, "tJ t'T1 L·ngim'en111: & E11v1romnt1mal C 011s.11/ta11t5. Inc. or: BRITT RICE ELECTRIC. LP r-- 1 I ------....J ' -i ~' t'T1 x l> en l> < -------.,_ ~ ~ ........ r ' ~ '~ . ' .W. P RKWAY BURTON CREEK DRAINAGE BASIN AUDIO VIDEO COLLEGE STATION, TX PROJECT : Audio Video LOCATION : Coll e Station , Texas APPR: MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DATE : 04/11/05 FIGURE NO.: 2 11 c s c f .ngifl<'l'fillg ('{ f ./l\'lfVll/W'11f(I/ C011511/trmu. Inc or: BRITT RICE ELECTRIC. LP AERIAL PHOTOGRAPH (2002) OF SUBJECT SITE AUDIO VIDEO COLLEGE STATION, TEXAS PROJECT : Audio Video LOCATION : Colle e Station Tx APPR: MFC REV . DATE : DRAWN BY : MOK SCALE : As Shown DATE : 04 /11/05 FIGURE NO .: 3 / !1 c / / I -GENERAL DIRECTION OF SURFACE STORMWATER RUNOFF PROPERlY LINE ,.,, CONTOUR LINE OF EXIST ELEVATION SITE AREA: 22,215.60 SQ . FT. OR .51 ACRES t:!QIE I INFORMATION PRESENTED IN TH IS DRAWING IS FOR INFORMATIONAL PURPOSES ONLY AND NOT INTENDED TO BE USED IN CONSTRUCTION. ,--------------------, _ I \ \ \ /- Subject Site \ Undeveloped Grass Covered Area I ! \ l I \ I I I rz -------------------1 J Adjacent Site ! I\.._ I I I )j n n \j \ s c rngifn><~ring ~ }4'11\'lrOIJllJl'IJl<lf Cn11.H1/ta11ts, lnr. PROJECT: Audio Video LOCATION: Coll e Station, TX BRITT RICE ELECTRIC . LP APPR: MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DATE: 04/11/05 FIGURE NO.: 4 SOURSE : FIRM Map, Number 48041C0142C Effective Date July 2 , 1992 l .ngwrering & l .m·tronmemaf Cmnulwnu, Inc. or: BRITT RICE ELECTRIC . LP Z ONE A AREA OF SUBJECT PROPERTY AUDIO VIDEO COLLEGE STATION TX PROJECT: Audio Video LOCATION : Coll e Station, Texas APPR: MFG REV. DATE : DRAWN BY: MOK SCALE: AS SHOWN DATE: 04/11/05 FIGURE NO .: 5 . ' j I KEY: AREA OF STORM WATER DETENTION = 4,376 FT2 (0R 0 .10 ACRES) - - - -LDT BOUNDARIES r--::---- --~ -- --- --- ----- ""/LDT 3F ---- ~; ./ I Connect Prop. StorM Exist. StorM Sewer ------1..U ' / Areo or Prop. StorMwtl ter u Ft ntlO n I ~ ~Exist. StorM Sewer\\_ Ex ist LDT 3A r . I ~-~te Exis t . Po. ed Ar.ea. L n~f!111eeri11~ & I m·1rn11mental Cn11::.ulta11a.l11< PROJECT: Audio Video LOCATION : Coll e Station, TX BRITT RICE ELECTRIC. LP APPR: MFC REV. DATE: DRAWN BY: MDK SCALE: AS SHOWN DA TE : 04/11/05 FIGURE NO .: 6 .. liQIE INFORMATION PRESENTED IN THIS DRAWING IS FOR INFORMATIONAL PURPOSES ONLY AND NOT INTENDED TO BE USED IN CONSTRUCTION . KEY; j I ----PROPERlY LINE GROUND COVER I : PCC PAVING AND SIDtWALKS . AREA = 4,978 FT (OR 0 .11 ACRES) ~ BUILDING LAYOUT 2 AREA = 8, 11 5 FT (OR 0 . 17 ACRES) E '<t ' "<I VEGETATION 2 AREA = 10,800 FT (OR 0 .25 ACRES) 40 0 40 FEET TOTAL AREA = 23, 175.41 FT2 ~I ~E1~=~E4=~~~=§1 (OR .53 ACRES) c s c r ,-"""""""' -""~~ ,--..-~ -..,.....,.. -~~~,---or-~ -~ ,,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~1 ~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,. I I ,~ ,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~, ~ ~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,I r:nl~l!Jt'<'rin~ c{'. /,11\'lro11me11tol Consult<111B. l nc. I ,~'<t,~'<t,~'<t,~'<t,~'<t,~'<t,~~ 'I ~ '<t _,_~_. I >--~--t '<t '~ '<t ,. Q ~'<t i 1 'i \ \ \ I TYPES OF GROUND COVER ASSOCIATED \NITH POST-DEVELOPMENT SCHEME COLLEGE STATION, TX PROJECT: Audio Video LOCATION: Coll e Station, TX BRITI RICE ELECTRIC. LP APPR :MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DATE : 04/11/05 FIGURE NO .: 7 I c s c 9 8 7 6 5 Ill .... 0 4 0 3 2 0 Q POST • 4.83 cte 5 10 (600 sec.) Mlnumum Volume of Detention Ston:199 Sawin • Dlff-.nce In N9oe Bet_, Pre and Poot llowloprMnt Hydl"09f"CIPho lwa • 2,349 cult 15 TIME 20 (1200 sec .) PRE-AND POST-DEVELOPMENT UNIT HYDROGRAPHS FOR 100-YEAR STORM EVENT BRITI RICE ELECTRIC . LP AUDIO VIDEO COLLEGE STATION TEXAS 25 30 min . (1800 sec.) PROJECT : AUDIO VIDEO LOCATION : COLLEGE STAT ION TEXAS APPR : MF C REV . DATE : DRAWN BY : MOK SCALE : AS SHOWN DATE : FIGURE NO · 8 DRAINAGE REPORT FOR PROPOSED AUDIO VIDEO BUILDING UNIVERSITY DRIVE NEAR SPRING LOOP COLLEGE STATION, TEXAS Prepared for Britt Rice 3002 Longmire Dri ve Suite D College Station, TX 77845 Submitted to City of College Station Development Services 1101 Texas Avenue College Station, Texas 77842 Prepared by CSC Engineering & Environmental Consultants, Inc . 3407 Tabor Road Bryan , Texas 77808 April 2005 1!1.~e~ M. Frederick Conlin, P.E. Senior Engineer ; CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drain age Study Proposed Audio Video Building; College Station, TX TABLE OF CONTENTS Page 1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT ............................. .1 2.0 DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT .................................................. 1 2.1 SITE LOCATION ................................................................................................................. 1 2 .2 EXISTING SITE CONDITIONS .......................................................................................... 2 2.3 PROPOSED SITE DEVELOPMENT SCHEME .................................................................. 2 3 .0 LOCATION OF THE SITE WITHIN THE MAJOR DRAINAGE BASIN AND EXISTING DRAINAGE PATTERNS IN THE AREA OF THE SUBJECT SITE ....................... .3 4.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA ................................................... .3 5.0 STORM WATER RUNOFF COMPUTATIONS .......................................................................... .4 5.1 USE OF THE RATIONAL FORMULA ............................................................................... 4 5 .2 RUNOFF COEFFICIENTS (C) ............................................................................................ 5 5.3 TIME OF CONCENTRATION (Tc) ..................................................................................... 6 5.4 RAINFALL INTENSITY (1) ................................................................................................. 7 5.5 AREA OF SITE (A) .............................................................................................................. 7 5 .6 STORM WATER RUNOFF QUANTITIES ......................................................................... 7 6.0 STORM WATER DETENTION .................................................................................................... 9 6.1 REQUIRED MINIMUM DETENTION STORAGE VOLUME .......................................... 9 6.2 DETENTION BASIN STORAGE AREA ............................................................................ 10 6.3 DETENTION BASIN OUTLET STRUCTURE ................................................................... I 0 7.0 EROSION CONTROL MEASURES ............................................................................................. 12 7 .1 GENERAL CONSIDERATIONS ......................................................................................... 12 8.0 CERTIFICATION ........................................................................................................................... 12 9 .0 REFERENCES ................................................................................................................................ 13 LIST OFT ABLES Table 1. Summary of Determination of Runoff Coefficient (C) Values for Post-Development Conditions for Entire Site ...................................................................................................... 6 Table 2. Computed Rainfall Intensity Values for Defined Storm Return Period ................................ 7 Table 3. Calculation of Pre-and Post-Development Storm Water Runoff Quantities Using the Rational Method .................................................................................................................... 8 ,.. II CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7 . Figure 8. LIST OF FIGURES Vicinity Map Burton Creek Drainage Basin Aerial Photograph (2002) of Subject Site and Surrounding Area Pre-Development Site Conditions and Stormwater Runoff Flow Patterns FfRM Flood Plain Map of Area of Subject Property Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns Types of Ground Cover Associated With Post-Development Scheme Pre- and Post-Development Unit Hydrographs for 100-Y ear Storm Event Ill CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT This report documents the information used in the formulation of the stormwater drainage system for the proposed Audio Video Building development being constructed by Britt Rice Electric, L.P. (BRE) in College Station, Texas. 2.0 DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT Information concerning the project was provided by Mr. Kenny Walsh , Project Manager with BRE, the general contractor for the project, and by Mr. Brett Cumpton, AIA, with the project architects, Cumpton & Associates. 2.1 SITE LOCATION The property which is the subject of the proposed development and this drainage report is situated on the northern side of University Drive East, approximately 1,500 to 1,600 ft west of the intersection with Spring Loop (see Figure 1 -Vicinity Map in Appendix A; all figures referenced in the report are in Appendix A). The site is situated within the Burton Creek Drainage Basin (Figure 2 -Burton Creek Drainage Basin). As can be seen from a review of Figure 3 -Aerial Photograph (2202) of Subject Site , existing commercial developments border the subject property to the south (David Gardener's Jewelers), west (Buffalo Wild Wings restaurant), east (office park), and north (Comfort Suites Hotel (currently under construction)). The proposed office building will be situated on an undeveloped lot that is referred to as Lot 3R of Block V of the University Park Addition -Phase II. The subject site is located immediately behind Lot 3A of the referenced subdivision. Lot 3A is currently occupied by the David Gardener's Jewelers building that has a physical address of 911 University Drive East. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 2.2 EXISTING SITE CONDITIONS The subject site extends over an area of approximately 0.53-acre and is undeveloped, being covered by short gasses and a few isolated trees as indicated in the aerial photograph in Figure 3. The subject site has a pronounced slope in a northerly direction toward the adjacent Comfort Suites Hotel site. The predominant direction of stormwater surface runoff flows follows the surface grade toward the hotel site as illustrated in Figure 4 -Pre-Development Site Conditions and Storm Water Runoff Flow Patterns. Surface grades vary across the site from approximately 2.7 to 5 percent, but average approximately 3 percent. Burton Creek is situated approximately 2,500 ft to the north of the project site and north of Spring Loop and Autumn Circle (Figure 1) In addition, there is a small, unnamed tributary drainage swale approximately 500 ft west of the subject site that flows in a northerly direction to Burton Creek (Figures 1, 2 and 3). The proposed site is not located within any existing flood plains as illustrated on Figure 5, FIRM Flood Plain Map of Area of Subject Property. 2.3 PROPOSED SITE DEVELOPMENT SCHEME The proposed development will consist of a single-story office/retail building of approximately 8, 115 square feet in area and associated paved dri veway and parking areas of approximately 4,978 square feet in area as illustrated on Figure 6 -Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns. CSC anticipates that the proposed office building structure will be situated in the southwestern portion of the previously described property as illustrated in Figure 6. We also anticipate that the proposed office building will have a single sloped roof that slopes to the north. We further anticipate that the proposed paved area will be located east of the proposed building (Figure 6) and will provide access to a drive-in bay of the building, as well as provide parking spaces for approximately eight vehicles. Additional parking will be provided by "off-site" paved areas on the adjacent lot (Lot 3A) that is currently occupied by David Gardener's Jewelers. We anticipate that the paved drive and parking areas associated with the new building will be constructed of a rigid pavement system with a Portland cement concrete (PCC) surface. Landscaping of the site will be established in the areas immediately around the office building and in the islands and areas bordering the paved access drive and parking area. 2 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX The finished floor slab elevation of the building will be at approximately El. 319 .5. The finished floor elevation will require some small volumes of fill to be added to the southern portion of the site in order to achieve fmal grades in the building pad area. Greater thicknesses of fill will be required in the northern area of the site. We anticipate that the fill heights will vary from 0.5 ft in the southern portion of the building pad to approximately 4 feet in the northern portion of the pad . Finally, we do not anticipate that the building will have a basement or a storm shelter or other features that would require structural excavations at the site. 3.0 LOCATION OF THE SITE WITHIN THE MAJOR DRAINAGE BASIN AND EXISTING DRAINAGE PATTERNS IN THE AREA OF THE SUBJECT SITE As previously discussed , the subject 0.53-acre site is located in the middle reaches or middle portion of the Burton Creek drainage basin (Figures 1 and 2). The subject site is located approximately 2,500 feet south of the Burton Creek channel. The subject site is situated at a point within the drainage basin that is approximately 3,400 feet downstream of the junction of Tributary C of Burton Creek and the main channel of Burton Creek, and approximately 3,600 feet upstream from the point where Burton Creek flows into Carters Creek (see Figure 1). There are no distinct drainage channels across the existing site. The major portion of current storm water runoff from the site appears to be by sheet-flow in a northerly direction toward the adjacent hotel site. The stormwater runoff previously flowed across the hotel site to various pavement sections along Spring Loop or private roadways adjacent to Spring Loop where the collected storm water runoff was routed via street gutters to existing storm sewer curb inlets. The storm water collected in the curb inlets was then discharged through a system of storm sewer pipes into Burton Creek, which , as previously mentioned, is situated north of the subject property. 4.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA This report described the planned storm water drainage system for the proposed development and addresses the volume of storm water detention required following the planned development of the building and associated paved areas . Both the site and the proposed development scheme were evaluated 3 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX in accordance with the criteria outlined in the "Drainage Policy and Design Standards (DPDS)" manual of the City of College Station, Texas. The DPDS manual is undated but contains a chapter on "Flood Hazard Protection" that has a revision date of October 1, 1990. This report also discusses general erosion control measures. 5.0 STORM WATER RUNOFF COMPUTATIONS 5.1 USE OF THE RATIONAL FORMULA The Rational Formula was used to compute the volume of storm water runoff prior to and following the planned development. Calculations based upon the Rational Formula were employed to assess the quantity of storm water that must be detained to "offset" the increased runoff associated with the new development. The generalized grading of the site and the general direction of pre-development flow are illustrated on the accompanying Figure 4. The proposed grading plan for the development and the patterns of post-development storm water runoff flows are illustrated on the accompanying Figure 6 . Use of the Rational Formula is reasonable for this project since the contributory area of runoff is less than 50 acres, an area sometimes referenced in the literature as an upper limit for use of the Rational Formula. In addition, the subject site is located within a Secondary Drainage System and not within a Primary Drainage System. The Rational Formula is not recommended for use within a Primary Drainage System . Therefore, the Rational Formula was used to determ ine the peak discharge for both pre-and post- development conditions . The general equation for the Rational Formula is well known: Q=CIA where Q = discharge of storm water in units of cubic feet per second ( cfs) C = coefficient that represents the average runoff characteristics of the land cover within the drainage area of interest, i.e., the runoff coefficient, which is dimensionless I= rainfall intensity in units of inches per hour (in/hr), and A = area of the site that contributes to the storm water runoff in units of acres 4 ·. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX The values of each of the factors contained in the equation that were employed to compute the storm water runoff at the subject site are discussed in the following section s . 5.2 RUNOFF COEFFICIENTS (C) The runoff coefficients or "C" values were computed for both pre-and post-development conditions . Coefficients for the different types of surface covers were determined from Table ill-I of the DP DS manual. The coefficient for the pre-development condition was determined based upon the land cover category listed in Table ill-I as a combination of ''Natural Woodlands" and ''Natural Grasslands " for slopes in the range of 1% to 3.5%. A range of C-values of 0.18 to 0.25 is listed in the referenced table for the ''Natural Woodlands" and a range of C-values of 0.35 to 0.45 was given for ''Natural Grasslands" for the cited topographic conditions. Accordingly, an average value of 0.4 was selected for use for pre- development cover of the entire 0.53-acre site . An average C-value for post-development conditions was also calculated . The post-development C-values were determined from the referenced table in the DPDS for the specific types of site cover associated with post-developed site conditions. An illustration of the various types of site cover anticipated for post-development conditions is presented in Figure 7 -Typ es of Ground Cover A ssociated With Pos t-Development Scheme . The specific types of post-development cover materials illustrated in Figure 7, the corresponding C-values from Table III-I of the DPDS manual , and the approximate areas of the various types of cover materials listed in Figure 7 were used in the analysis outlined in Table I of this report to compute an average C-value for the post-developed site. In general , a unit C-value of 0.9 was used for building roof and concrete covered pavements and sidewalks and a unit C-value of 0 .5 was used for the landscaped or grassed areas as indicated in Table I . Therefore , the average C-value for the post-developed site can be determined by dividing the summation of the product of the individual areas times the respective unit C-values li sted in Table 1 and dividing that summation by the overall site area which is also listed in Table 1. The result of that calculation is as follows: Average C-value = summation of unit C-values times individual areas divided by the total site area Average C-value = 17 ,184 C-square feet I 23 ,894 square feet = 0 .71 5 ·. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX Table 1. Summary of Determination of Runoff Coefficient (C) Values for Post-Development Conditions for Entire Site Area of Area of Typical Extended Multiplication Type of Ground Cover Coverage, Coverage, C-Values of square feet Acres C-Values time Area, sq ft Concrete (sidewalks, streets, etc .) 4,978 0.11 0.90 4,480 Building roof 8,1 15 0.17 0.90 7,304 Grassed or landscaped areas 10,801 0.25 0.50 5,400 Summation 23,894 0.53 17,184 5.3 TIME OF CONCENTRATION (Tc) The time of concentration at a site is used to determine the intensity of the rainfall event used for computing storm water flows and required detention volumes. The time of concentration is defined as "the time required for the runoff to be established and flow from the most remote part of the drainage area to the point under design." For pre-development conditions the time of concentration for the subject site was calculated based upon the elevation difference and the flow distance from the higher elevations in the southern portion of the property to the lower elevations is the northern portions of the site adjacent to the hotel site to the north The referenced change in elevation is 4 ft and the referenced distance is approximately 220 ft. This grade produces a slope of approximately 2% for pre -development conditions . The slope for post-development conditions was determined from the proposed site grading plan and drainage patterns as illustrated in Figure 6. The surface slopes or grades and the velocities presented in Table ill-2 of the DPDS manual were used to determine the appropriate storm water runoff velocity. For overland or sheet-flow over slopes in the range of 0 to 3 percent, such as are present at the subject site, velocities of runoff flow are listed to be in the range of 0 to 1.5 feet per second (fps) for natural woodlands and in the range of 0 to 2.5 fps for natural grasslands. An average velocity of2 fps was conservatively selected for pre-development conditions. Thus, time of travel between the location of the higher elevations of the site and the lower elevations of the site was calculated to be approximately 110 seconds (220 ft distance/2 fps velocity) or approximately 1.8 minutes for pre-development conditions. The post-development time of concentration was calculated over the paved areas of the site without consideration of any detention and was determined to be a shorter time period. Therefore, a minimum time of concentration of 10 minutes (as specified in the DPDS manual) was used in the calculations for both pre-and post-development conditions. 6 ·. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 5.4 RAINFALL INTENSITY (I) The rainfall intensity values were computed for the minimum 10-minute time of concentration previously discussed using the intensity-duration-frequency curves developed by the Texas Department of Transportation. The computed intensities calculated for storm events with "return periods" of 5, 10, 25 , 50, and 100 years are indicated in Table 2. Table 2. Computed Rainfall Intensity Values for Defined Storm Return Period Storm Return Period (Years) 5.5 AREA OF SITE (A) 5 10 25 50 100 Rainfall Intensity (Inches/Hour) 7.7 8 .6 9 .9 11.1 12.3 The area of the site used in the computation of storm water runoff is the original site area of 0.53 acres as indicated on Figures 4 and 6. 5.6 STORM WATER RUNOFF QUANTITIES Storm water runoff quantities were calculated using the Rational Formula. Runoff quantities were calculated for both pre-and post-development conditions for the 0.53 -acre site for storm events with recurrence intervals of 5, 10, 25, 50 and l 00 years. The rainfall intensities used in the computations were as discussed in Section 5.4. The results of the computations are presented in Table 3. 7 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii Report of Drainage Study Proposed Audio Video Building; Coll ege Station, TX ------------------------------------------------------ Tab le 3 . Calculation of Pre-and Post-Development Storm Water Runoff Quantities Using the Rational Method PRE-POST-DIFFERENCE Storm Area I ntensityc DE VELOPMENT DEVELOPMENT IN FLOWS E vent (acres) (in ches (year ) /hr) Cpre a Cpost8 Q post Q o dless dless (cfs) (cfs) 5 0 .53 7.7 0 .4 0 0.7 1 2.90 1.27 10 0 .53 8 .6 0.40 I 1.82 0.71 3.24 1.42 25 0 .53 9 .9 0.40 { 2.10 0.71 3.73 1.63 50 0.53 11. l 0.40 2.35 0.71 4.1 8 1.83 100 0.53 12.3 0.40 \ 2.61 0 .71 4.rh 2.02 •Average valu es o f C we re obtained fro m Tab le Ill -I of the DPDS ~Ji 7 b dl ess = dim ensionl ess 0 Valu es o btained fro m Tabl e 2 of thi s report 8 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 6.0 STORM WATER DETENTION 6.1 REQUIRED MINIMUM DETENTION STORAGE VOLUME CSC has noted that the proposed site is relatively small and occupies an area of only 0.53-acres. In addition, a significant portion of the site will remain as landscaped areas following development. As can be seen from a review of Table 2, approximately 47 percent of the site will still be landscaped. Therefore, the difference in pre-and post-development flows for any storm recurrence interval will be relatively small. The storage volume of the detention area was calculated such that the peak discharge of the ultimate development hydrographs for the 100-year design storm was limited to a discharge less than a defined target discharge. The defined target discharge was characterized by the DPDS manual to be the peak discharge of the pre-development hydrograph for the 100-year storm event. Since the entire 0.53- acre site is being developed at the present time, the current developed condition and the ultimate developed condition were assumed to be the same. The required detention storage volume was determined as the difference in area between the pre- and post-development hydrographs , as depicted on Figure 8 The Triangular Approximation method was used to determine the hydrographs. The hydrographs were constructed by assuming that the peak discharge, as calculated from the Rational Formula, occurs at a time equal to the time of concentration and that one-third of the flow volume occurs before the peak discharge is reached and two-thirds occur following the peak discharge . The Triangular Approximation method of developing hydrographs is generally considered to be acceptable for analysis of Secondary Drainage Systems with an area of less than 50 acres, which is applicable to the drainage basin addressed in this report. The difference in area between the two hydrographs, or the required minimum volume of the detention storage area, was calculated to be approximately 1,818 cubic feet for the 100-year recurrence interval storm event. 9 CSC ENGINEERING & ENVJRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 6.2 DETENTION BASIN STORAGE AREA We propose to provide the required detention storage within the planned paved area on the eastern side of the proposed building, which is indicated by the blue shading on Figure 6. The required volume for storm water detention will be created by depressing the pavement surface and the corresponding top of the storm water catch basin inlet within the paved area to an elevation that is below the surrounding perimeter curb elevations and also below the high break points in the pavement grading. The proposed detention area will have a square to rectangular shape as depicted on Figure 6 and will have approximate plan dimensions of 64 feet by 80 feet with some interior parking islands excluded . The area of the stormwater detention basin was determined to be approximate 4,376 square feet (sq ft). The stormwater inlet box at the approximate center of the detention basis will serve as the outlet for the captured storm water is discussed in greater detail in the following section of this report. The elevation of the top of the storm water inlet box was established at approximately 10 inches or 0 .83 feet below the elevation of the high break point in the pavement grade to the south of the inlet box and well below the top elevation of the curbs surrounding the detention area. Therefore, approximately l 0 inches or 0.83 feet of water could pond at the inlet location . The depth of ponded water is expected to vary from 10 inches at the inlet location to 0 inches at the curb and high break point locations, with an average depth of approximately 5 inches or 0.42 feet over the entire area. The maximum depth of ponding of l 0 inches or 0.83 feet is permitted for parking areas used as detention basins according to the DPDS (page 74). No higher elevations of ponding are possible since an overflow of the high break point in the paving would occur for ponded depths above 10 inches, and the stormwater would flow to the adjacent paved area of the existing storm water catch basins in the David Gardener's Jewelers parking lot. The approximate volume provided by the proposed detention basin was computed by multiplying the area of the detention basin (4 ,376 sq ft) by an average ponded water depth of 5 inches (0.42 ft). The computed detained volume was approximately 1,838 cubic feet (cu ft). As previously stated , the required minimum storage volume of the detention basin would be approximately 1,818 cu ft in order to detain the difference between the I 00-year event storm water runoff for pre-and post-development conditions. The minimum required volume of 1,818 cu ft is within the available storage capacity of the proposed detention basin . 6.3 DETENTION BASIN OUTLET STRUCTURE As previously indicated , the outlet structure for the detention basin will consist of the grated inlet that will be constructed in the proposed paved area east of the proposed building. The grate across the top 10 CSC ENGINEERING & ENVIRONMENT AL CONSULT ANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX of the box will be chosen so that it will pass a flow that is approximately equal to the maximum pre- development flow of 2.61 cfs for the 100-year storm recurrence interval. The flow through the grate will be calculated based upon a maximum depth of ponded water of l 0 inches (0.42 feet). The flow capacity of any inlet grate in a sump or ponded condition is a function of both the depth of water over the grate and the total clear opening area of the grade. The flow can generally be determined by the following equation: Q =CA ('1(2 gd)) where Q = flow rate through the grate inlet in cfs C =orifice coefficient,~ 0.67 for grate inlets, dimen sion less A = clear opening of grate, square inches g =acceleration constant of gravity, ~ 32.2 feet per square second (ft/sec2) or 2.683 inches per square second (in/sec2) d = depth of water over grate, feet The equation can be simplified to ... Q = 0 .0108 A ('-id) where Q = flow rate through the grate inlet in cfs A = clear opening of grate, square inches ~ 32.2 feet per square second (ft/sec2) or 2.683 inches per square second (in/sec2) d = depth of water over grate, feet The referenced equation is generally valid for inlet grates in a sum p condition where water depths are 4 inches are greater. At water depths less than 4 inches the inlet grate acts as a weir to incoming flow and requires different analysis to determine flow capacity. Substituting the desired flow of2.61 cfs and the 10 inch depth of water over the grate inches, the approximate open area of the grate that is required can be determined as follows: Q = 0.0108 A ('-id) 11 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building ; College Station, TX 2.61cfs =0 .0108 A ('./10 inches) or ... A= (2.61 cfs) I [0.0108 x '110 inches]= 2.61 cfs/0.03 solving ... A = 76.4 square inches The catch basin designated by East Jordan Iron Works , Inc. as model or catalog number V-5714 has an opening of 75 square inches , which is approximately equal to the required opening area of 76.4 square inches. The referenced grate inlet or its equivalent has been specified on the construction drawings for the referenced grated box inlet. 7.0 EROSION CONTROL MEASURES 7 .1 GENERAL CONSIDERATIONS The erosion control measures proposed at the site will basically consist of silt fences that are placed on the three (3) down -gradient boundaries of the site . We do not anticipate the need for hay bale barriers, rock dams or sedimentation traps since there will not be any channelized or concentrated flows produced by the construction operations. The locations and detailing of the proposed erosion control measures are depicted on Sheet C-7 of the submitted construction plans. 8.0 CERTIFICATION "I hereby certify that this drainage report for the 0.53-acre site that is referred to as Lot 3R of Block V of the University Park Addition -Phase II and which is the site of the proposed Audio Video Building in College Station , Texas, was prepared under my supervision in accordance with the previsions of the C ity of College Station "Drainage Policy and Design Standards (1990)" for the owners thereof." '21.~ emi)~.~ M. Frederick Conlin , Jr., P.E. I Registered Professional Engineer State of Texas P.E. Number 44481 12 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. Report of Drainage Study Proposed Audio Video Building; College Station, TX 9.0 REFERENCES Chow, Ven T., Maidment, David R ., and Mays, Larry W . 1988. Applied Hydrology . McGraw-Hill Book Company. New York, NY. 1988 . City of College Station, Texas. 1990. "Drainage Policy and Design Standards," part of the Stormwater Management Plan for the City of College Station. October, 1, 1990. Davis, Victor D., and Sorensen , Kenneth E. 1969 . Handbook of Applied Hydraulics. McGraw-Hill Book Company . New York, NY . 1969. Federal Emergency Management Agency. Flood Insurance Rate Map; Brazos County Texas and Incorporated Areas; Panel 142 of250. FIRM Map Number 48041C0142 C, Effective Date: July 2, 1992. Hann, C . T ., Barfield, B. J., and Hayes, C. J. 1994. Design Hydrology and Sedimentology for Small Catchments . Academic Press, Inc. San Diego, CA. 1994. Mason, John M. and Rhombrerg, Edward L. 1980 . On-Site Detention . Prepared for Texas Engineering Extension Service, Texas A& M University. College Station , TX. 1980. Publication No. PWP: 03355-01. McCuen, Richard H. A Guide to Hydrologic Analysis Using SCS Methods. Prentice-Hall , Inc. Englewood Cliffs, NJ. 1982. United States Department of Agriculture. 1975. Urban Hydrology for Small Watersheds. Technical Release No. 55. Engineering Division, Soils Conservation Service, U .S. Department of Agriculture. January 1975. Wanielista, Martin P. 1978. Stormwater Management Quantity and Quality. Ann Arbor Science. Ann Arbor, Ml. 1978. Westaway, C.R. and Loomis, A. W. 1979. Cameron Hydraulic Data. (16th Edition). Ingersoll-Rand. Woodcliff Lake, NJ. 1979. 13 ·. Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6 . Figure 7. Figure 8. CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. FIGURES Vicinity Map Burton Creek Drainage Basin Aerial Photograph (2002) of Subject Site and Surrounding Area Pre-Development Site Conditions and Stormwater Runoff Flow Patterns FJRM Flood Plain Map of Area of Subject Property Proposed Site Development Scheme (Post-Development Conditions), Site Grading Plan, and Surface Storm Water Runoff Flow Patterns Types of Ground Cover Associated With Post-Development Scheme Pre-and Post-Development Unit Hydrographs For 100-Year Storm Event 11 c s c l .11~u11cc1111g & L m·11011111cmal CmB11lra11rs. I m or: BRITT RICE ELECTRIC . LP ! I VICINITY MAP AUDIO VIDEO COLLEGE STATION , TEXAS PROJECT: Audio Video LOCATION : Colle e Station TX APPR: MFC REV. DATE : DRAWN BY : AEA SCALE : AS SHOWN DATE: 04/11/05 FIGURE NO .: 1 UNIVERSITY OR . \ ' I I \ / I 11gineeri11g A'. Fndromnemal ron'j11/ia11h. l11c. BRITT RICE ELECTRIC. LP r-- 1 I ------...J ---- BURTON CREEK DRAINAGE BASIN AUDIO VIDEO COLLEGE STATION, TX PROJECT: Audio Video LOCATION : Coll e Station , Texas APPR: MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DATE : 04/11/05 FIGURE NO .: 2 11 c s c /.ngin<·erin~ c{' /.m·irmmwmal Cons11/ranB. l11c. or: BRITT RICE ELECTRIC . LP AERIAL PHOTOGRAPH (2002) OF SUBJECT SITE AUDIO VIDEO COLLEGE STATION , TEXAS PROJECT : Audio Video LOCATION : Colle e Station , Tx APPR: MFC REV. DATE : DRAWN BY: MOK SCALE: As Shown DATE : 04/11/05 FIGURE NO.: 3 / c s c \ -GENERAL DIRECTION OF SURFACE STORMWATER RUNOFF PROPERlY LINE CONTOUR LINE OF EXIST ELEVATION SITE AREA: 22,215.60 SQ. FT. OR .51 ACRES MQIE - INFORMATION PRESENTED IN THIS DRAWING IS FOR INFORMATIONAL PURPOSES ONLY AND NOT INTENDED TO BE USED IN CONSTRUCTION. Subject Site \ Undeveloped Grass Covered Area I ! \ , l I \ ! I 1 ! [l ----------~ --------~ I Adjacent Site ( I I I I /i ~ n \j l .'ngint'f'ring ,( r11dronme111al C01uultt111ts. l11c. PRE-DEVELOPMENT SITE C NDITI N AND STORM WATER RUNOFF FLOW PATTERNS AUDIO VIDEO BUILDING E E T Tl PROJECT: Audio Video LOCATION : Coll e Station, TX (- BRITT RICE ELECTRIC. LP APPR: MFC REV. DATE: DRAWN BY: MDK SCALE: AS SHOWN DATE: 04/11/05 FIGURE NO .: 4 SOURSE : FIRM Map, Number 48041C0142C Effective Date July 2, 1992 I c s c L'ngineering c( l.'m·ironmenral (' OfllllfltJIJU, /!u. or: BRITT RICE ELECTRIC. LP AREA OF SUBJECT PROPERTY AUDIO VIDEO COLLEGE STATION TX PROJECT: Audio Video LOCATION : Coll e Station, Texas APPR: MFG REV. DATE : DRAWN BY: MOK SCALE: AS SHOWN DATE: 04/11/05 FIGURE NO .: 5 ! I j I AREA OF STORM WATER DETENTION = 4 ,376 FT2 (0R 0 .10 ACRES) - - - -LDT BOUNDARIES Connect Prop. StorM Exist. StorM Sewer ------W \ Areo o r Prop. StorMwt>.ter DF' _ntlo n I v-LDT 3A ~Exist. StorM Sewer\\_Exist r Gro E! I nl e-t Exist . Po ed Areo 11 \ l .ngineering & /"11\'fronmental Cons11/wnts, Inc. or: BRITI RICE ELECTRIC. LP PROP. SITE DEVELOPMENT SCHEME (POST DEVELOPMENT CONDITIONS), SITE GRADING PLAN, AND SURFACE WATER R N FF FL W PATIERN PROJECT: Audio Video LOCATION: Coll e Station , TX APPR: MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DATE: 04/11/05 FIGURE NO.: 6 • . • ~ INFORMATION PRESENTED IN THIS DRAWING IS FOR INFORMATIONAL PURPOSES ONLY AND NOT INTENDED TO BE USED IN CONSTRUCTION. Ka; j I ----PROPERlY LINE GROUND COVER I PCC PAVING AND SID~WALKS ~-~-AREA = 4,978 FT (OR 0 .11 ACRES) ~ BUILDING LAYOUT 2 AREA = 8, 115 FT (OR 0.17 ACRES) f ~ ' 4 VEGETATION 2 AREA = 10,800 FT (OR 0 .25 ACRES) 40 0 40 FEET TOTAL AREA = 23, 175.41 FT2 ~W~,___.~=~E45~~E§I (OR .53 ACRES) r '-"""""""" -~..,.--.... ,--or-~ -T"""'lll" -~ ....-'f"' ,~~ -~ ,,~~,~~,~~,~~,~~,~~,~~,~~,~~,~i .~ ~ '~ ~ '~ ~ '~ ~ '~ ~ '~ ~ '~ ~ '~ ~ '~ ~ '~ ~ ,. I I ,,~ ,~~,~~,~~,~~,~~,~~,~~ r ~~,~~,~~,~~,~~,~~,~~,1 'I ~ ~ I ;--____ ---., ~ ' ~ ~ ' I 9 ~~I 1 ,, I }- n 11 \ 1.:11swet>ri11s. ct r~11\'irnnlfw11tt1! ConJ11/ta11H.f 11c TYPES OF GROUND COVER ASSOCIATED WITH POS~DEVELOPMENTSCHEME COLLEGE STATION, TX PROJECT: Audio Video LOCATION : Colle e Station, TX BRITI RICE ELECTRIC. LP APPR: MFC REV. DATE: DRAWN BY: MOK SCALE: AS SHOWN DA TE: 04/11/05 FIGURE NO.: 7