Loading...
HomeMy WebLinkAboutCT 02-25; NORTHPARK LA COSTA; STORM WATER MANAGEMENT PLAN; 2004-02-24STORM WATER MANAGEMENT PLAN for NORTHPARK AT LA COSTA City of Carlsbad Track No. 02-25 Prepared by: Snipes-Dye Associate* Dated: January 6, 2004 Revised: February 4, 2004 Job No. CA1133 TABLE OF CONTENTS Page 1. DESCRIPTION OF PROPOSED PROJECT 1 2. ANTICIPATED AND POTENTIAL POLLUTANTS GENERATED BY PROPOSED PROJECT J A. Pollutants from Project Area I B. Pollutants of Concern 2 C. Conditions of Concem 2 3. ESTABLISH POST-DEVELOPMENT STORM WATER BMPs 3 A. Site Design BMPs 3 B. Source Control BMPs 3 C. Treatment Control BMPs 4 4. CONSTRUCTION BMPs 4-6 5. ONGOING STORM WATER BMP MAINTENANCE 6 6. SUMMARY/CONCLUSION 7 7. REFERENCES 8 APPENDIXES Appendix A- Overview of Carlsbad Watershed Beneficial Water Uses of Carlsbad Watershed Appendix B- Water Quality Standards Inventory Database of San Marcos Creek Appendix C- Site Hydrology/Hydraulic Analysis (Pre and Post-Conditions) Appendix D- Site Plan 1. DESCRIPTION OF PROPOSED PROJECT The project is located on the southwest corner of Levante Street and La Costa Avenue, in the City of Carlsbad, San Diego County, California (Assessor Parcel Numbers 223-170-21 & 22). The site is bounded by La Costa Avenue to the north, Levante Street to the east, single-family residences to the west and town homes to the south. The site is approximately 1.54 acres. The site is currently vacant, but it has been previously graded in 1972 to 1974. The existing pads on the site are separated in elevation, approximate 8 feet, more or less. There is no existing vegetation on the site, excepting four existing street trees along the Levante Street right-of- way. The site runoff does not accommodate any offsite runoff. The drainage over the site is via surface flow toward the southwest, discharging on to Levante Street then into the City of Carlsbad storm drain system. According to the USDA Conservation Sen/ice Soil Survey, San Diego Area, California published in December 1973, the survey classifies the project surface soils as HrC2, Huerhuero loam with surface slopes in the 5 to 9% range. The Huerhuero soil consists of moderately well drained loams that have clay subsoil. The mean annual precipitation is between 10 to 12 inches. The available soil capacity of holding water is 4 to 5 inches. In a representative profile, the surface layer is brown and pale-brown loam about 12 inches thick. The upper part of the subsoil is brown, moderately alkaline clay (to the depth of 41 inches or more). Below it, brown, mildly alkaline clay loam and sandy loam extends to a depth of 60 inches or more. The erosion hazard is moderate. The project proposes to construct 12 detached multi-family residential units. The project proposes to have accesses from Levante Street to a new 24- foot wide private road, Corte Tradicion. The existing water and sewer services shall be killed. Water and sewer mains will be extended along Corte Tradicion, the proposed private road, to serve the new residences. 2. ANTICIPATED AND POTENTIAL POLLUTANTS GENERATED BY PROPOSED PROJECT A. Pollutants from Project Area - The site is within the San Marcos Creek Hydrologic Area (904.5) which is part of Carlsbad Watershed. The impaired water body pollutants which were recently listed in the Clean Water Act Section 303(d) are copper, lead, zinc, cadmium, coliform bacteria, sedimentation, nutrients and eutrophic. San Marcos Creek is listed as 303(d)-impaired water bodies for coliform bacteria. According to the Table 2 in The City of Carlsbad Standard Urban Stomn Water Mitigation Plan (April 2003), the Anticipated and Potential Pollutants Generated by the Detached Residential Development are as follows: Sediments (anticipated) Nutrients (anticipated) Trash & Debris (anticipated) Oxygen Demanding Substances (anticipated) Oil & Grease (anticipated) Bacteria & Viruses (anticipated) Pesticides (anticipated) B. Pollutants of Concem - Based on the impaired water bodies list and the pollutants generated by land use type, the primary pollutants of concem for the proposed project are sediments and coliform bacteria, nutrients, sediment, trace metals, and toxics. C. Conditions of Concem - The project site is contributory to the San Marcos Creek Hydrologic Subarea (904.5) of the Carlsbad Hydrologic Area (904.0) which consists of approximately 210 square miles of watershed. This project area represents approximately 0.001 percent of the total watershed. Peak stonnwater discharges from the site in the pre- development conditions during the 100-year, six-hour intensity stomi will be approximately 4.04 cubic feet per second. The peak stormwater discharges from the site in the post-development conditions during 100- year, six-hour intensity storm will be approximately 5.24 cubic feet per second. The increase of peak discharge is due to the increase of impervious surface areas. PRE-DEVELOPMENT POST-DEVELOPMENT 0% OF IMPERVIOUS SURFACE AREAS 61% OF IMPERVIOUS SURFACE AREAS The site currently generates sediments, trash and debris, due to the uncontrolled runoff discharging over unprotected bare land. The post-development site shall reduce the sediments as well as trash and debris which are the primary pollutants of concern from the development. 3. ESTABLISH POST-DEVELOPMENT STORM WATER BMPs A. Site Design BMPs - The proposed project consists of 12 detached two-story residences with a 24-foot wide access private road. Approximately 61% of the site is impervious surface including rooftops, concrete drives, walkways, parking areas and private road. 1) The project proposes to construct two-story buildings with minimum driveway and walkway widths to maximize building density and minimize impervious surface areas. 2) The post-development drainage is designed to drain runoffs from rooftops and impervious surface areas into the adjacent landscaping areas prior to discharging off site. 3) The existing slopes along the northwesterly boundary will be protected by the installation of retaining walls at the tops of slopes; the runoffs are also directed away from the slopes. B. Source Control BMPs - Preventing the pollutants from generating or controlling the pollutant sources is the most effective way to treat the pollutants. Installation of the treatment BMP devise near the pollutant source is better than treating the polluted water at the downstream. 1) There will be no outdoor storages of material. Therefore, the potential for toxic compounds, oil and grease, heavy metals, nutrients and suspended solids to enter storm drain system is reduced or eliminated. The use of landscape fertilizers will be controlled and utilized sparingly. Fertilizer use will be controlled in accordance with local, state and federal regulations. The use of pesticides is a potential pollution source. Pesticide use will be eliminated to the most practicable extent. When pesticide use is necessary, pesticides will be applied in accordance with local, state, and federal regulations. 2) There will be no outdoor trash enclosure. The individual residence shall store trash in containers with attached lids. The schedule of trash pick up is weekly, so they should never be over-filled. Site grounds will be maintained and litter collected and properly disposed of. Driveways will be maintained, litter collected, and periodically swept. 3) The 12 proposed residences are sharing one 24-foot paved private road, Corte Tradicion. The runoff from this private road is collected in a vegetated basin, located at the southwest comer of the property. Driveways and vehicle parking areas are potential sources of oil and grease pollution. Areas of vehicle activity will be maintained and periodically swept. Any spills shall be clean up immediately. C. Treatment Control BMPs - The proposed development is classified as a priority project. The design of the treatment control BMP structure of the project is required. 1) The project proposes to construct a 70'x4.17' retention basin, located at the southwest corner of the site. See the calculations in the attached Hydrology/Hydraulic Analysis in Appendix D. 2) The pollutant sources of the development are the access driveways, the private road. The runoffs from these areas are directed to the vegetated retention basin which equipped with bio-filter turf to control sediments and other pollutants. 3) The drainage and treatment system of the development project have a very minimal potential to affect ground water. The stormwater runoff from most impervious surface is pretreated by flowing through landscaping areas prior to discharging into the retention basin for volume treatment. 4. CONSTRUCTION BMPs The following BMPs listed and detailed in the Construction Activity, Best Management Practices Handbook, published by Camp, Dresser, and McKee, March 1993 are selected as being appropriate for this specific site and should be implemented during the constmction phase. It is important that the selected construction BMP's are maintained and functional during the construction period and until all permanent BMPs are fully operational. • ESC1- Scheduling: This activity provides for the sequencing of construction activities to reduce the amount and duration of soil exposed to erosion by wind, rain, runoff and vehicle tracking. • ESC10- Seeding and Planting: Normally done at the conclusion of site disturbance to become a permanent BMP, seeding and planting of grasses, shrubs, trees and/or ground covers provides long-term stabilization of soil. " ESC11- Mulching: Mulching is used to temporarily or permanently stabilize cleared or freshly seeded areas. Hydro seed is an example of seed and mulch being placed at the same time. Hydro seed is expected to be used to mitigate surface soil disturbance occurring in the process of constructing the retention basin. ESC20- Geotextiles and Mats: Matting made of natural or synthetic materials may be used to temporarily stabilize slope areas and shallow swales. ESC21- Dust Control: Dust control measures are used to stabilize soil from wind erosion, and reduce dust generated by construction activities. Periodic watering will address these issues. ESC24- Stabilized Construction Entrance: A stabilized pad of aggregate underlain with filter cloth located at the point where traffic will enter or leave the construction site will significantly reduce the amount of sediment tracked off-site. ESC30- Earth Dike: The temporary earth dike shall be used to channel drainage from the graded pads to temporary sediment traps (see ESC55). ESC30- Earth Dike: The temporary earth dike shall be used to channel drainage from the graded pads to temporary sediment traps (see ESC55). ESC31- Drains and Swales: Temporary drains and swales shall be used to divert runoff around the construction site, to divert runoff from stabilized areas around disturbed areas and to direct runoff into sediment traps. ESC50- Silt Fence: A silt fence that detains sediment-laden water shall be used at the down slope limits of site disturbance to promote sedimentation behind the fence, while releasing the water. ESC52- Gravel Bag Barrier: Stacking gravel bags along a level contour creates a barrier, which detains sediment-laden water, ponding water upstream of the barrier and promoting sedimentation. ESC55- Sediment Trap: Sediment traps shall be used to settle out sediment from runoff leaving the site. CA 2- Paving Operations: Prevent or reduce the discharge of pollutants from paving operations, using measures to prevent runon and runoff pollution, properly disposing of wastes and training employees and subcontractors. CA 3- Structure Construction and Painting: Prevent or reduce the discharge of pollutants to storm water from structure construction and painting by enclosing or covering or berming building material storage areas, using good housekeeping practices, using safer altemative products and training employees and subcontractors. CA 10- Material Storage and Delivery: Prevent or reduce the discharge of pollutants to storm water from material delivery and storage by minimizing the storage of hazardous materials on-site, storing materials in a designated area, installing secondary containment, conducting regular Inspections and training employees and subcontractors. • CA 11- Material Use: Prevent or reduce the discharge of pollutants to storm water from material use by using alternative products, minimizing hazardous material use on-site and training employees and subcontractors. • CA 12- Spill Prevention and Control: Prevent or reduce the discharge of pollutants to storm water from leaks and spills by reducing the chance for spills, stopping the source of spills, containing and cleaning up spills, properly disposing of spill materials and training employees. • CA 20- Solid Waste Management: Prevent or reduce the discharge of pollutants to storm water from solid or construction waste by providing designated waste collection areas and containers, arranging for regular disposal and training employees and subcontractors. • CA 23- Concrete Waste Management: Prevent or reduce the discharge of pollutants to storm water from concrete waste by conducting washout off-site, performing on-site washout in a designated areas and training employees and subcontractors. • CA 24- Sanitary Waste Management: Prevent or reduce the discharge of pollutants to storm water from sanitary waste by providing convenient, well-maintained facilities and arranging for regular service and disposal. • CA 31- Vehicle and Equipment Fueling: Prevent or reduce the discharge of pollutants to storm water by using off-site facilities, fueling in designated areas only, enclosing or covering stored fuel, implementing spill controls and training employees and subcontractors. • CA 40- Employee/Subcontractor Training: Employee/subcontractor training likes maintenance or a piece of equipment, is not so much a best management practice as it is a method by which to implement BMP's. The responsibility of implementing and maintaining the above BMP's during the construction period shall reside with the licensed contractor who is responsible for overall project construction management. In the event the owner chooses to be the project manager, the responsibility will reside with the owner. 5. ONGOING STORM WATER BMP MAINTENANCE The proposed permanent BMPs are private and within the project property. It is a responsibility of the owner/developer/applicant to ensure the installation of these mechanisms by incorporating into the project final construction plans which will be reviewed and approved by the City of Carlsbad. It is also a responsibility of the owner/developer/applicant to Implement an Inspection and maintenance schedule/program for the permanent BMPs which are appropriate and approved by the City of Carlsbad. The maintenance program Is shown below. PERMANENT BMP INSPECTION & MAINTENANCE SCHEDULE STRUCTURE LOCATION INSPECTION & MAINTENANCE RESPONSIBLE PARTY SIDEWALK UNDERDRAIN PIPES (D-27) ALONG NORTHERLY RIGHT-OF-WAY OF LEVANTE STREET HOME OWNER ASSOCIATION (MONTHLY) CURB-OUTLET (D-25) ALONG NORTHERLY RIGHT-OF-WAY OF LEVANTE STREET HOME OWNER ASSOCIATION (MONTHLY) ON-SITE AREA DRAINS ON LOTS 1, 10, 11 & 12 HOME OWNER ASSOCIATION (MONTHLY) BIO-FILTER TURF ON LOT 12 HOME OWNER ASSOCIATION (MONTHLY) 6. SUMMARY/CONCLUSION This Storm Water Technical Report has been prepared In accordance with The City of Carlsbad Standard Urban Stormwater Mitigation Plan (SUSMP) dated April 2003. This pian has Identified the primary potential pollutants, established the post-development BMPs (Site Design BMPs, Source Control BMPs and Treatment BMPs). The plan also Indicates some of the construction BMPs which may be utilized during the construction phase. The proposed uses of the property will Insignificantly impact the receiving water body beneficial uses, If the specified best management practices are effectively Implemented. 7. REFERENCES- The following references were used in the preparation of this plan: • The City of Carlsbad Standard Urban Stormwater Mitigation Plan • County of San Diego Watershed Protection, Stormwater Management, and Discharge Control Ordinance • Storm Water Quality Handbooks, Project Planning and Design Guide, CalTrans (State of California Department of Transportation), Camp Dresser & McKee, Inc., May 2000. • Staff Report for Standard Urban Storm Water Mitigation Plans and Numerical Sizing Criteria for Best Management Practices, California Regional Water Quality Control Board, San Diego Region, 2001. • California Storm Water Best Management Practice Handbooks (Construction Activity and Municipal), Camp Dresser & McKee, et al March 1993. • California Storm Water Best Management Practice Handbooks (Industrial/Commercial), Camp Dresser & McKee, et al, March 1993. site LoCftTio/^ a cn c 5 < < Z<n Water Quality Standards Inventory Database Water Quality Standards Inventory Database Page 1 of 3 Click on the links below to search for another waterbody. Search by Beneficial Uses Search by Keyword Search by SWRCB Region Search by Caltrans District Search by County Chck on the links below to view water quality parameters for San Marcos Creek. Beneficial Uses Water Quality Objectives Water Quality Narrative Constituents Water Quality Numeric Criteria Water Quahty Bacteria Criteria Click on the links below to view comments and corrections logged or to navigate to the comments and corrections input page. Comments and Corrections Logged Comments and Corrections Input Page San Marcos Creek Water Quality Control Board Region: Click on the region number for a list of waterbodies and reported hydrologic units in that region. 9 Hydrologic Units: Click on the reported hydrologic unit for a list of waterbodies in that unit. Reported Hydrologic Units Published Hydrologic Units Hydrologic Units: Click on the reported hydrologic unit for a list of waterbodies in that unit. 9()4.51 904.51 Caltrans District: Click on the Caltrans district for a list of waterbodies and reported hydrologic units in that district. ii Counties: Click on the reported county name for a list of waterbodies and reported hydrologic units in that county. *Please note that reported and published counties are associated with hydrologic unit, not waterbody. Reported Counties Published Counties SAN DIEGO Location Map Watershed Map V:' - '!;;;;;«;• ;r;i-<,si m 1 Geospatial Waterbody System Assessment Data SAN MARCOS CREEK (Includes 305(b) and 303(d) Determinations) Waterbody Beneflcial Uses RWQCB Beneficial Use Click on the beneficial use for the beneficial use code and description. Use Status Potential or Existing Existing Water Contact Recreation Existing Non-Contact Water Recreation Existing Warm Freshwater Habitat Existing Wildlife Habitat Existing http://endeavor.des.ucdavis.edu/wqsid/waterbody.asp?wb_fkey=3709 1/16/04 Water Quality Standards Inventory Database Page 2 of 3 Water Quality O jj ectives Waterbody Reach Beneficial Use Constituent Constituent Concentration Constituent Units Constituent Details Constituent Comments NA ALL Boron 0.75 mg/L - NA ALL Chloride 250 mg/L • NA ALL Color 20 Units - NA ALL F 1 mg/L NA ALL Iron 0.3 mg/L - NA ALL Manganese 0.05 mg/L - NA ALL MBAS 0.5 mg/L - NA ALL Sodium 60 mg/L - NA ALL Sulfate 250 mg/L - NA ALL TDS 500 mg/L - NA ALL Turbidity 20 NTU - Water Quality Narrative Constituents Constituent Name Constituent Description Biostimulatory Substances Inland surface waters, bays and estuaries and coastal lagoon waters shall not contain biostimulatory substances in concentrations that promote aquatic growth to the extent that such growths cause nuisance or adversely affect beneficial uses. Color Waters shall be free of coloration that causes nuisance or adversely affects beneficial uses.The natural color offish, shellfish or other resources in inland surface waters, coastal lagoon or bay and estuary shall not be impaired. DO The dissolved oxygen concentration in ocean waters shall not at any time be depressed more than 10 percent from that which occurs naturally, as the result ofthe discharge of oxygen demanding waste materials. Floating Material Waters shall not contain floating material, including solids, liquids, foams, and scum in concentrations which cause nuisance or adversely affect beneficial uses. Oil and Grease Waters shall not contain oils, greases, waxes, or other materials in concentrations which result in a visible film or coating on the surface ofthe water or on objects in the water, or which cause nuisance or which otherwise adversely affect beneficial uses. , pH The pH value shall not be changed at any time more than 0.2 pH units from that which occurs naturally .Changes in normal ambient pH levels shall not exceed 0.2 units in waters with designated marine (MAR), or estuarine (EST), or saline (SAL) beneficial uses. Changes in normal ambient pH levels shall not exceed 0.5 units in fresh waters with designated cold freshwater habitat (COLD) or warm freshwater habitat (WARM) beneficial uses. In bays and estuaries the pH shall not be depressed below 7.0 nor raised above 9.0. In inland surface waters the pH shall not be depressed below 6.5 nor raised above 8.5. Radioactivity Radionuclides shall not be present in concentrations that are deleterious to human, plant, animal, or aquatic life nor that result in the accumulation of radionuclides in the food web to an extent that presents a hazard to human, plant, animal or aquatic life. Sediment The suspended sediment load and suspended sediment discharge rate of surface waters shall not be altered in such a manner as to cause nuisance or adversely affect beneficial uses. Suspended Solids Waters shall not contain suspended and settlable solids in concentrations of solids that cause nuisance or adversely affect beneficial uses. Toxicity All waters shall be maintained free of toxic substances in concentrations that are toxic to, or that produce detrimental physiological responses in human, plant, animal, or aquatic life. Compliance with this objective will be determined by use of indicator organisms, analyses of species diversity, population density, growth anomalies, bioassays of appropriate duration, or other appropriate methods as specified by the Regional Board. The survival of aquatic life in surface waters subjected to a waste discharge or other controllable water quality factors, shall not be less than that for the same water body in areas unaffected by the waste discharge or, when necessary, for other control water that is consistent with requirements specified in US EPA, State Water Resources Control Board. As a minimum, compliance with this objective as stated in the previous sentence shall be evaluated with a 96-hour acute bioassay. In addition, effluent limits based upon acute bioassays of effluents will be prescribed where appropriate, additional numerical receiving water objectives for specific toxicants will be established as sufficient data become available, and source control of toxic substances will be encouraged. Temperature The natural receiving water temperature of intrastate waters shall not be altered unless it can be demonstrated to the satisfaction ofthe Regional Board that such alteration in temperature does not adversely affect beneficial uses. At no time or place shall the temperature ofany COLD water be increased more than 5F above the natural receiving water http://endeavor, des.ucdavi s. edu/wq sid/waterbody.asp?wb fkey=3709 1/16/04 Water Quality Standards Inventory Database Page 3 of 3 temperature. Taste and Odor Waters shall not contain taste or odor producing substances at concentrations which cause a nuisance or adversely affect beneficial uses. The natural taste and odor offish, shellfish or other Regional water resources used for human consumption Shall not be impaired in inland surface waters and bays and estuaries. Turbidity Waters shall be free of changes in turbidity that cause nuisance or adversely affect beneficial uses. Water Quality Numeric Criteria Beneficial Use Numeric Constituent Name Numeric Constituent Detail Numeric Constituent Maximum Numeric Constituent Units Numeric Constituent Comments Numeric Constituent Reference WARM Dissolved Oxygen --5 mg/L AGR Boron 0.75 mg/L Quality Criteria for Waten 1986-Gold Book. Water Quality Ammonia Criteria Beneficial Use Constituent Name Constituent pH Constituent Temperature Constituent Time Duration Constituent Concentration Constituent Units AGR Ammonia as N --0.ii2> mg'L RECl Ammonia as N ---0.025 mg/L REC2 Ammonia as N --• 0.025 mg/T WARM Ammonia as N --0.025 mg/L wn.D Ammonia as N ---0.025 mg/L Water Quality Bacteria Criteria Beneficial Use Constituent Name Constituent Concentration Details Constituent Concentration Constituent Units Constituent Comments Constituent Reference RECl Fecal Coliform Log Mean-10% of Samples for 30 day 400 Count per IOO ml Log mean value. Based on more than 10 percent of total samples during any 30-day period. RECl Fecal Coliform Log Mean-5 Samples for 30 day 200 Count per 100 ml Log mean value. Based on a minimum of not less than five samples for any 30-day period. REC2 Fecal Coliform Average-10% of Samples for 30 day 4000 Count per 100 ml Average value. Based on more than 10 percent of total samples during any 30-day period. REC2 Fecal Coliform Average-for 30 day 2000 Count per 100 ml Average value. Based on samples for a 30-day period. Comments Comments Click above to go to the Comments input page. Hi, I'm having problems linking to San Marcos creek from the Geospatial Waterbody System Assessment Data for 303(d) determination. Please let me know where or when I could get this information. Thanks, Louie © Information Center for thc Environment info(g).ice.ucdavis.edu \ Search | Notices | http://endeavor, des.ucdavis.edu/wqsid/waterbody.asp?wb fkey=3 709 1/16/04 HTDROLOGY/HYDRAVUC ANALYSIS FOR Carlsbad Tract No. 02-25 North Park at La Costa Suite G 2910 460-2033 William A. Snipes TOUCHSTONE COMMUNITY TM File: CA1133 1/6/04 SUMMARY PROJECT DESCRIPTION: THE PROJECT PROPOSES TO DEVELOP 14 LOTS TO INCLUDE 12 LOTS WITH DWELLING UNITS AND 2 COMMON LOTS FOR ACCESS DRIVEWAY AND LANDSCAPE COMMON AREA ONTO TWO (2) VACANT LOTS, LOT 227 AND 228 OF SUBDIVISION MAP NO. 7457. CURRENT SITE CONDITIONS: THE SUBJECT SITE IS LOCATED ON AN ELEVATED PAD WITH THE TOPOGRAPHY SLOPING AWAY IN ALL DIRECTIONS. IT IS BOUND TO THE EAST AND THE SOUTH BY LA COSTA AVENUE AND LEVANTE STREET, RESPECTIVELY; TO THE WEST, IT IS BOUND BY MULTI-FAMILY RESIDENTIAL AND SINGLE- FAMILY RESIDENTIAL TO THE NORTH. THE RUNOFF FROM THE PROPERTY SHEET-FLOWS SOUTHERLY DISCHARGING INTO PUBLIC RIGHT-OF-WAY, LEVANTE STREET. NO OFF-SITE RUNOFF DISCHARGES ONTO THE SUBJECT SITE. EXISTING RUNOFF: THE SUBJECT SITE HAS PREVIOUSLY GRADED INTO 2 PADS AND FLOWS FROM THE NORTHEAST CORNER OF THE SITE TO THE SOUTHWEST CORNER OF THE SITE, WHICH IS THE LOW POINT THE RUNOFF FROM THE SUBJECT SITE IN THE CURRENT CONDITION IS 4.04 CFS IN THE 100-YEAR, 6-HOUR STORM. POST-DEVELOPMENT RUNOFF: THE POST-DEVELOPED SITE DIVIDES THE SITE INTO 2 DRAINAGE BASINS, NORTHERLY BASIN AND SOUTHERLY BASIN, 0.92 ACRES AND 0.55 ACRES, RESPECTIVELY. THE NORTHERLY HALF OF THE SITE INCLUDES THE PROPOSED LOTS 1 TO 7, 14 AND PORTION OF LOT 13 OF THE PROPOSED TENTATIVE MAP. SURFACE DRAINAGE FROM THE NORTHERLY BASIN SHEET FLOWS TO A DETENTION BASIN, WHICH IS LOCATED AT THE SOUTHWEST CORNER OF THE PROJECT SITE THEN DISCHARGING TO THE PUBLIC RIGHT- OF-WAY, LEVANTE STREET, BY A CURB OUTLET. THE SOUTHEASTERLY HALF OF THE SITE INCLUDES LOTS 8 TO 12 AND PORTION OF LOT 13 OF THE PROPOSED TENTATIVE MAP. SURFACE DRAINAGE SHEET FLOWS TO PUBLIC RIGHT-OF-WAY, LEVANTE STREET. THE ATTACHED DETENTION BASIN DESIGN CALCULATIONS SHOW THAT THE POST DEVELOPMENT RUNOFF DISCHARGE SHALL NOT EXCEED THE PRE- DEVELOPMENT RUNOFF DISCHARGE IN THE 100-YEAR, 6-HOUR STORM. Prepared By: Drainage-Summaiy.doc Snipes-Dye Associates i TOUCHSTONE COMMUNITY TM File: CA1131 1/6/2004 SITE PEAK FLOW DETENTION (100-YEAR) DETERMINE VOLUME OF INCREASED RUNOFF FROM THE DEVELOPED STTE IN THE 6-HOUR, 100-YEAR STORM: 1. DETERMINE WEIGHTED SITE RUNOFF COEFFICIENT FOR CURRENT STTE. 2. DETERMINE WEIGHTED SITE RUNOFF COEFFICIENT FOR DEVELOPED SITE. 3 DETERMINE PEAK RUNOFF FROM THE CURRENT SITE AND THE DEVELOPED SITE IN THE 6-HOUR, 100-YEAR STORM. 4. PREPARE SITE HYDROGRAPH FOR THE DEVELOPED SITE. 5. DETERMINE VOLUME FOR INCREASED RUNOFF FROM THE DEVELOPED SITE. 6. DETERMINE RETENTION BASIN WITH INCREASED RUNOFF VOLUME: 1. CALCULATE WEIGHTED RUNOFF COEFFICIENT fCI FOR THE CURRENT STTE: I 1= 1.37 ACRES (A1 = 1.37 ACRES, ASSUME C1 = 0.55) \ 1= 0.18 ACRES (A2 = 0.18 ACRES, ASSUME C2 = 0.70) A=A1+A2 C = {A1(C1) +A2(C2)}/A C = (1.37(0.55) + 0.18(0.70)} -r 1.54 C = 0.57 2. CALCULATE WEIGHTED RUNOFF COEFFICIENT fCJ FOR THE DEVELOPED SITE: I 1= 0.58 ACRES (A3 = 0.58 ACRES, ASSUME C3 = 0.40) I I = 0.06 ACRES (A4 = 0.06 ACRES, ASSUME C4 = 0.70) \^^= 0.91 ACRES (A5 = 0.91 ACRES. ASSUME C5 = 0.95) A=A3 + A4+A5 C = {A3(C3) + A4(C4) + A5(C5)}/A C = (0.58(0.40) + 0.06(0.70) + 0.91(0.95)} ^1.54 0 = 0.74 Prepared by: Snipes-Dye Associates 1 100-YR Calculations TOUCHSTONE COMMUNITY TM File: CA1131 1/6/2004 3. CALCULATE PEAK DISCHARGE OF CURRENT STTE: ASSUME Tc = 10 MINUTES FOR CURRENT AND DEVELOPED SITE. UTILIZE FIGURE 3-1 INTENSITY/DURATION CURVE AND ISOPLUVIALS OF 100-YEAR 6-HOUR PRECIPITATION READ INTENSITY (I) = 4.6 INCH/HOUR Q = CIA C = 0.57, / = 4.6in/hr, A = 1.54 acres 0 = 0.57(4.6)1.54 Q = 4.04 cfs 4. CALCULATE PEAK DISCHARGE OF DEVELOPED STTE: Q = CIA C = 0.74,1 = 4.6in/hr, A = 1.54acres 0 = 0.74(4.6)1.54 Q= 5.24 cfs Prepared by: Snipes-Dye Associates 2 100-YR Calculations TOUCHSTONE COMMUNITY TM 5. CALCULATE VOLUME OF INCREASED RUNOFF FROM DEVELOPED STTE: DEVELOPED STTE HYDROGRAPH Q(cfs) x=1.15 File: CA1131 1/6/2004 5 10 ^ Tc (MINUTES) AREA UNDER SHADED AREA = VOLUME OF DISCHARGE FROM DEVELOPED SITE VOLUME = 1.15(1.20)(60) = 82.80 CU. FT. (MIN. VOLUME OF STORMWATER TO RETAIN) TOTAL PRE-DEVELOPMENT DISCHMtGE FROM STTE (Q ex): Qex =4.04 cfs TOTAL POST-DEVELOPMENT DISCHARGE FROM STTE (Qpr): Qpr = 5.24 cfs THE POST-DEVELOf^ENTDISCHARGE RUNOFF THROUGH RETENTION BASIN (Qin): Qin= Z91 cfs (See attacfted calculaiions) THE POST-DEVELOPMENT DISCHARGE RUNOFF NOT THROUGH RETENTION BASIN (Qnr): Qnr = Qpr - Qin = 5.24 cfs - 2.91 cfs Qnr = 2.33 cfs THE MAX. ALLOWABLE POST-DEVELOPMENT DISCHARGE RUNOFF PRIOR TO RETAIN (Q r): Qr = Qex - Qnr =4,04 cfe - Z33 cfe Qr = 1.71 cfs UWze 2-4 inch PVC pipes for the proposed retention basin outlet 4" pipe's discharge capacity = 0.84 cfe ^ee attadied calculations) 2-4"pipes = 2x0.84 = 1.68 cfs < Qr THE TOTAL POST-DEVELOPMENT RUNOFF = Qnr+Q (two 4" pipes) = 2.33 cfs+ 1.68 cfs = 4.01 cfe 4.01 cfs (the total post-development runoff) is less than 4.04 cfs (the total pre-development runoff) Prepared by: Snipes-Dye Associates 100-YR Calculations TOUCHSTONE COMMUNITY TM File: CA1131 1/6/2004 6. DESIGN RETENTION STRUCTURE WTTH MINIMUM VOLUME OF 82 CUBIC FEET: (See attached detsal) RETENTION VOLUME (V) = CROSS-SECTION BASIN AREA (A) X WIDTH OF BASIN (W) A = 1/2 X WATER LEVEL HEIGHT (H) X LENGTH OF WATER SURFACE (L) 6" OVERFLOW PIPE RETENTION BASIN DIMENSIONS: W = 4.17 FEET H = 0.67 FEET Hrt. = 1/100 L = 100(H) = 67 FEET V=ACW} = 172L(H)(W) V=(67 FT)(0.67 FT)(4.17 FT)/2 V=94 CU. FT. > 82 CU. FT. DETERMINE THE OVERFLOW PIPE: UWze one 6"pfpe for tfie retmtmn basin overflow pipe 6" overflow pipe's discharge capacity = 2.55 cfs (See attadied calculadons) Q(enter) - Q (two 4' pipes) = Q(mln. overflow pipe) 2.91 cfs - 1.68 cfs = 1.23 cfs < 2.55 cfe (TtK capacity ofa 6" overflow pipe is greats ttian ttie required runoff discliarge.) CONCLUSION: THE TWO 4" PVC PIPE OUTLET AT THE BOTTOM OF THE LOW-END OF THE PROPOSED RETENTION BASIN AND ONE 6" PVC OVERFLOW PIPE. WHICH HAS AN INVERT ELEVATION AT 8" ABOVE THE BOTTOM OF THE LOW-END ARE SUFFICIENT TO RET/MN THE REQUIRED VOLUME OF STORM WATER AND DRAIN THE DEVELOPED SITE DURING A PEAK FLOW, 100-YEAR STORM EVENT. Prepared by: Snipes-Dye Associates 100-YR Calculations 6" PVC OVERFLOW PIPE ^ 2-4' PVC PIPES DISCHARGE TO CURB OUTLET QD(6CH*H«E"I-68 CFS •RETAINING WAU. -^TB^'ON VOUAe (V, - I05 CU. FT. PS? GRADING PLAN (TYP.) SECTION A-A NO SCALE DRAINAGE PIPES DISCHARGE K TO CURB OUTLET PER ^ IMPROVEMENT PLANS (TYP) O RETAINING WALL PER GRADING PLAN (TYP.) PLAN VIEW - RETENTION RASIN DETAiL NO SCALE ~ HYDRAULIC ELEMENTS - I PROGRAM PACKAGE (C) Copyright 1982-99 Advanced Engineering Software (aes) Ver. 8.0 Release Date: 01/01/99 License ID 1305 Analysis prepared by: Snipes-Dye Associates 8348 Center Drive, Suite G La Mesa, CA 91942-2910 Fax (619)460-2033 Phone (619)697-9234 TIME/DATE OF STUDY: 11:52 8/ 7/2002 DISCHARGE CAPACTTY OFA 4" PIPE »»PIPEFLOW HYDRAULIC INPUT INFORMATI0N«« PIPE DIAMETER(FEET) = 0.330 FLOWDEPTH(FEET) = 0.330 PIPE SLOPE(FEET/FEET) = 0.4900 MANNINGS FRICTION FACTOR = 0.020000 »»> NORMAL DEPTH FLOW (CFS) = 0.84 HYDRAULIC ELEMENTS - I PROGRAM PACKAGE (C) Copyright 1982-99 Advanced Engineering Software (aes) Ver. 8.0 Release Date: 01/01/99 License ID 1305 Analysis prepared by: Snipes-Dye Associates 8348 Center Drive, Suite G La Mesa, CA 91942-2910 Fax (619)460-2033 Phone (619)697-9234 TIME/DATE OF STUDY: 8:11 8/ 8/2002 DISCHARGE CAPACTTY FO A 6" PIPE ******** *****************************^,i,**.k***^,^,*^c*******^,ir*********** »»PIPEFLOW HYDRAULIC INPUT INF0RMATI0N«« PIPE DIAMETER(FEET) = 0.500 FLOWDEPTH(FEET) = 0.500 PIPE SLOPE(FEET/FEET) = 0.4900 MANNINGS FRICTION FACTOR = 0.020000 »»> NORMAL DEPTH FLOW (CFS) = 2.55 TOUCHSTONE COMMUNITY File: CAI 131 9/19/2003 RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-99 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/99 License ID 1305 Analysis prepared by: Snipes-Dye Associates 8348 Center Drive, Suite G La Mesa, CA 91942-2910 Fax (619)460-2033 Phone (619)697-9234 LEVANTE STREET TENTATIVE MAP POST-DEVELOPMENT CONDITIONS TOUCHSTONE COMMUNITY FILE NAME: CA1131.DAT TIME/DATE OF STUDY: 14:49 8/27/2002 USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.700 SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE =0.95 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED FLOW PROCESS FROM NODE 1.00 TO NODE 2.00 IS CODE = 21 »»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS««< *USER SPECIFIED(SUBAREA): MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .7400 INITIAL SUBAREA FLOW-LENGTH = 495.00 UPSTREAM ELEVATION = 295.45 DOWNSTREAM ELEVATION = 284.33 ELEVATION DIFFERENCE = 11.12 URBAN SUBAREA OVERLAND TIME OF FLOW(MINUTES) = 11.008 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.276 SUBAREA RUNOFF(CFS) = 2.91 TOTAL AREA (ACRES) = 0.92 TOTAL RUNOFF (CFS) = 2.91 Post-Dev.doc TOUCHSTONE COMMUNITY File: CA1131 9/19/2003 FLOW PROCESS FROM NODE 2.00 TO NODE 3.00 IS CODE = 4 »»>COMPUTE PIPEFLOW TRAVELTIME THRU SUBAREA««< »»>USING USER-SPECIFIED PIPESIZE««< DEPTH OF FLOW IN 6.0 INCH PIPE IS 3.9 INCHES PIPEFLOW VELOCITY(FEET/SEC.) = 21.5 UPSTREAM NODE ELEVATION = 287.00 DOWNSTREAM NODE ELEVATION = 279.60 FLOWLENGTH(FEET) = 15.00 MANNING'S N = 0.013 GIVEN PIPE DIAMETER (INCH) = 6.00 NUMBER OF PIPES = PIPEFLOW THRU SUBAREA(CFS) = 2.91 TRAVEL TIME(MIN.) = 0.01 TC(MIN.) = 11.02 FLOW PROCESS FROM NODE 4.00 TO NODE 5.00 IS CODE = 21 »»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS«<« *USER SPECIFIED(SUBAREA): MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .7400 INITIAL SUB7UREA FLOW-LENGTH = 200.00 UPSTREAM ELEVATION = 294.00 DOWNSTREAM ELEVATION = 286.78 ELEVATION DIFFERENCE = 7.22 URBAN SUBAREA OVERLAND TIME OF FLOW (MINUTES) = 5.974 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.325 SUBAREA RUNOFF(CFS) = 1.17 TOTAL AREA (ACRES) = 0.25 TOTAL RUNOFF (CFS) = 1.17 FLOW PROCESS FROM NODE 6.00 TO NODE 7.00 IS CODE = 21 »»>RATIONAL METHOD INITIAL SUBAREA ANALYSIS««< *USER SPECIFIED(SUBAREA): MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .7400 INITIAL SUBAREA FLOW-LENGTH = 100.00 UPSTREAM ELEVATION = 291.00 DOWNSTREAM ELEVATION = 285.00 ELEVATION DIFFERENCE = 6.00 URBAN SUBAREA OVERLAND TIME OF FLOW (MINUTES) = 3.566 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. TIME OF CONCENTRATION ASSUMED AS 6-MINUTES 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.325 SUBAREA RUNOFF(CFS) = 1.40 TOTAL AREA (ACRES) = 0.30 TOTAL RUNOFF (CFS) = 1.40 END OF RATIONAL METHOD ANALYSIS Post-Dev.doc Directions for Application: (1) From precipitalion maps determine 6 hr aiul 2A Iw iiniounts for the selected frequency. These maps are included in the County Hydrology Manual (10, 50, and 100 yr maps induded in the Design and Procedure Manual). (2) Adjust 6 hr precipitalion (if necessary) so lhal il is wilhin the range of 45% to 65% of lhe 24 hr precipilalion (nol applicaple to Desert). (3) Plot 6 hr precipitation on the right side of llie chail. (4) Draw a line Ihrough the point parallel lo the plotted lines. (5) This line is the intensity-duration curve for llie localion being analyzed. Intensity-Duration Design Chart - Template HazMal/Counly . jgeology Uanual/lnt_Dur Design Chart.FHB F I a ll R p. 3-1 C Y OF SAN DIEGO J.ATME//T OF SAfniATlON & •-JD CO/iTROL 33' IOO-YEAF P^ECIPITATIOij ^6' I 20-/ ISOPLUVIALS PnECIPITATIOn IM OF 100-YEAR 6-HOUR IHTMS or AM i;:c5i Picpn U.S. DEPARTMEN HATIONAL OCtANlC AND AT SPECIAL STUDIES U R AM Cl I, O F F| C E OF Ii 30' _ I •d by r OF COMMERCE QSPIIEHIC ADHIHISTRATION DBOLOGV. NATIONAL WEATHER SERVICE Y OF SAfI DIEGO _|RTM£»T OF SANITATION & FLOOD CONTftOL 33' 30 15' ii5 U.S. DEPARTMEN NATIONAL OCliA.SIC AND Al;. SPECIAI. STUDIES UKA.NCII, OFI ICi; OF ir 100-YEAI#^4-IIOl ll PRECIPITATIOW '^20-^ISQPLUVIALS 0 PnECIPITATIOfI in ir J 100 -YEAR 24-l(0UR EfJTHS OF AN INCH 30 M I I's! 30' l(i' 17' 30' in ir/