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Home My WebLink AboutDrainage Design Report I I 5 �, I •°\;:# I DRAINAGE DESIGN REPORT lit c'f I FOR I ESTATES OF WEST CLAY CARMEL, INDIANA I I Prepared for I The Reserve at S rin mill, L P P 9 P 0 Box 554 ICarmel, Indiana 46032 I IPrepared by Paul I Cripe, Inc 7172 Graham Road ' d '° ' Indianapolis, Indiana 46250 317) 842-6777 �,�QsQ�G%STE,Qs i.- � No. I g PE19500055I - Certified By -1 STATE OF f�c E....;3)9 . ,",�r,,:u si ,,,ta•�r,+1, Richar K: , P E IINDIAN REG `.0 9500055 IPIC#000389-20000 I I DRAINAGE DESIGN REPORT FOR Estates of West Clay I TABLE OF CONTENTS I1 0 Introduction . . .. . . . . ... . . 3 1 1 Project Description 3 I 1 2 Scope of Report 3 1 3 Existing Conditions 3 I 2 0 Hydrologic Method 21 Rainfall . . •• • .. ... ..... .. ... 4 4 2 2 Software 4 I3 0 Pre-Developed Drainage Analysis . . . . . . . 4 I 4.0 Post-Developed Drainage Analysis . . . . . . 5 4 1 Pond Design 5 I5 0 Comparison of Pre and Post-Developed Peak Discharges . 6 6 0 Conclusions . . .. .. . . . • •• • . 6 I Appendix A — Pre-Developed Drainage Analysis I Appendix B — Post-Developed Drainage Analysis Appendix D — Long Branch Floodway Study Appendix E — Maps I Exhibit One — Pre-Developed Drainage Basin Map Exhibit Two — Post-Developed Drainage Basin Map Exhibit Three —Offsite Map IExhibit Four— Soils Map I I I 1 I I1.0 Introduction I This report outlines the design of the storm water management system to serve Estates of West Clay at 131st Street and Ditch Road The scope of the report is to identify the design parameters for the storm water detention pond(s) that will serve the residential development and I to size the proposed storm sewer pipes The project is located within Clay Township, Hamilton County and is therefore subject to the design requirements of the Hamilton county Drainage Ordinance I1 1 Project Description I The proposed Development will be located on a 45 32-acre tract bounded by Ditch Road to the east, 131st Street to the south, A proposed residential development to the west, and a private residence to the north The project being undertaken by the Reserve at Spnngmill, L P will consist of the development of 25 single-family homes I1 2 Scope of Report I This report summarizes the design for the overall storm water management system for the entirety of the project, which consists of three wet detention ponds The ponds will be constructed of the project I1 3 Existing Conditions I The 45 32-acre site is undeveloped with the majority of the land used for farming The FIRM Map Panel No 180081-0002 C Effective Date of May, 19, 1981 indicates that the subject property is within a Flood Zone C classification On-site soils consist of Brookston, Crosby, and I Miami The site is generally level The runoff is currently discharged into two separate water sheds The north and east portion of the subject property drains into Almond Ditch via overland flow The south and west portion drains into Elliot Creek, which traverses through the Isouthwest corner of the property 2.0 Hydrologic Method IThe method used to generate runoff from the existing and proposed watersheds is the SCS unit hydrograph method of determining the peak flows that regulate the volume of retention pond needed Factors involved in the use of this method are the area of the watershed or basin, the I runoff coefficient (CN) and the time of concentration (Tc) The basin area is measured off the plans and survey The runoff coefficient is estimated based on the proposed land use conditions and the types of soils The time of concentration is determined from surface Iconditions and the slope of terrain 2 1 Rainfall Distribution IThe SCS 24-hour Type II Rainfall Distribution is used to calculate pre-developed peak flows and to size the detention ponds I 1 I I2 2 Software I After the input data and rainfall have been estimated, PondPack v7, a hydraulic modeling program, was used to determine the peak flows and volumes using the SCS TR-55 unit hydrograph method PondPack v7 generates an individual hydrograph for each basin and then the hydrographs can be added to generate runoff flows for ponds or to points of interest IPondPack v7 has a built-in time-of-concentration calculator with a minimum Tc of 5 minutes 3.0 Pre-Developed Drainage Analysis The ro ect site has been divided into Pre-developed basins Offsite contributions are identified P 1 P as well However, offsite runoff is omitted from the analysis since runoff from these offsite areas Iwill be "passed through"the site via drainage ways and discharged directly to the creek The peak discharge for each drainage basin for the 10-year storm has been calculated I The total on-site contribution from the Pre-developed 10-year 24-hour storm event is 96 29 cfs and for the 2-year 24-hour event is 52 00 cfs I Based upon these peak flows, the allowable peak discharge from a post-developed 100- year storm event is 96 29 cfs (on-site pre-developed 10-year peak) I Also, based upon these peak flows, the allowable peak discharge from a post-developed 10-year storm event is 52 00 cfs (on-site pre-developed 2-year peak) I4.0 Post-Developed Drainage Analysis The post-developed drainage analysis consists of the design of three detention ponds I4 1 Pond Design I The three detention ponds are designed to provide adequate storage volume to release a post- developed storm at acceptable rates in accordance with the requirements of the Hamilton County Surveyor's Office More specifically, to release the post-developed 100-year event at the U peak pre-developed 10-year rate and the post-developed 10-year event at the pre-developed 2- year rate The design of the ponds accounts for the full development of Estates of West Clay a residential subdivision I Some areas of the development will directly discharge under Ditch Road as shown on the post- developed drainage map The ponds have been sized to compensate for these direct discharges through over-retention The overall design provides sufficient storage volume to I release the combination of "stored" and "direct discharged" runoff at the pre-developed 10-year rate I Each pond will outlet through a single culvert structure and then will be routed directly to the respective drainage creek/ditch I The following summarizes the peak flow rates released from the on-site areas to be directly discharged and the release rates of the ponds during the 100-year 24-hour post-developed and 10-year 24-hour storm events I I I100-year Direct Discharge (Developed areas only) 12 90 cfs 100-year Peak Rate from Pond 1 32 72 cfs 100-year Peak Rate from Pond 3 8 93 cfs I10-year Direct Discharge (Developed areas only) 7 41 cfs I10-year Peak Rate from Pond 1 18 09 cfs, 0 Peak Rate from Pond 3 3 62 cfs II 5.0 e Comparison of Pre and Post-Developed Peak Discharge P p g I The following summary compares the total discharge from the ponds and direct discharge areas during the 100-year and 10-year post-developed events to the allowable release rate of the 10- year and 2-year pre-developed events The post-developed calculations include the Iacceptance of offsite basins Pre-developed 10-yr peak rate = 96 29 cfs IPost-developed 100-yr from ponds and direct discharge areas = 54 55 cfs IPre-developed 2-yr peak rate = 52 00 cfs Post-developed 10-yr from ponds and direct discharge areas = 29.12 cfs I6.0 Conclusions I The three proposed detention ponds are designed to provide sufficient storage volume to release the post-developed runoff at an acceptable rate as dictated by the Hamilton County Surveyor's Office The runoff associated with a post-developed 100 year storm event is I retained to release at a peak rate below the pre-developed 10 year rate Also, the runoff associated with a post-developed 10 year storm event is retained to release at a peak rate below the pre-developed 2 year rate I I I I I