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Home My WebLink AboutPD 2022-0024; 2780 JAMES DRIVE; DRAINAGE STUDY; 2022-12-12rev.4-14-23 revised 4-14-23 gac GAC Engineering 27475 Ynez Road #294 TEMECULA, CA92591 (760) 594-4889 April 14, 2023 DRAINAGE STUDY FOR: PD 2022-0024 DWG-539-5A LEGAL DESCRIPTION: LOT 5 OF TRACT NO.98-16RANCHO VERDE UNIT NO. 1, MAP NO. 14517 GR-2022-0039 2780 JAMES DRIVE CARLSBAD, CA 156-142-51 OWNER: VECK INVESTMENT PROPERTIES LLC 3276 HIGHLAND DRIVE CARLSBAD, CA 92008 INTRODUCTION Pre-Project Site Conditions and Drainage Patterns Narrative This project is located on an existing 0.20 Ac residential lot. The lot is a vacant residential lot with an existing residential pad to which will receive remedial earthwork to prepare the pad for a new residential structure, the lot frontage is to the existing cul-de- sac on James Drive. The site is gently sloping from the northeast high point to the southwest outfall in James Drive at approx. 2.0% and drains over existing vacant land, being pervious surfaces to the paved roadway in James Drive, onsite storm water to confluence with public water in James Drive thence to flows to existing curb and gutter in the southeast direction to an ex. 5’ wide curb inlet approx 95 lf downstream designed originally to accept the Sub-division runoff. Proposed Site Development and Drainage Patterns Narrative The proposed development will install a new single family residence and attached garage of hardscape of approx. 4865.0 SQ. FT. on the existing vacant lot. Although there is an increase in post-development runoff, overall the drainage flow pattern characteristics of the lot will be maintained. For all post-development basins P-101, P-102, storm water from the roof drains and over hardscape areas will be directed to impervious dispersion areas prior to outlet to the James Drive curb and gutter at node P-01 northwest side yard and at node P-02 for the southeast side yard will confluence with existing public flow in James Drive. During low flow conditions water is detained on site in the proposed impervious area dispersion zones, prior to being discharged to in James Drive Curb and gutter and confluence with public storm water runoff in the curb and gutter and thence for approx.95 lf flow in 6” curb and gutter to the southeast and is received in an existing 5’ wide curb inet. The 0.59 cfs is received into existing downstream public storm water conveyance storm drain system designed originally to accept the subdivision runoff with no anticipated negative down stream effect. A calculation is provided for the 5’ wide curb inlet opening showing that the inlet capacity is sufficient to receive the increase in storm water runoff from this residential development project. HYDRLOGIC CALCULATIONS AND RECOMMENDATIONS: PRE-DEVELOPMENT 1. DRAINAGE AREA: “E-101” Surface runoff water primarily as sheet flow over the vacant residential lot, no hardscape is present on the lot. Stormwater drains to the Southeast to confluence with public water in ex. James Drive at pre-development node p-1, thence flow in gutter to the southeast for approx. 95 lf to an existing 5’ wide curb inlet originally designed to accept the sub-division runoff. Q100E-101 has been determined to be 0.20 cfs at Pre-development outfall Node P-01. HYDRAULIC CALCULATIONS AND RECOMMENDATIONS: POST-DEVELOPMENT 2. DRAINAGE AREA: “P-101” Post development basin drainage is divided into 2 basins, Basins P-101, P-102. Basin P- 101 is primarily sheet flow from new residential patio areas and runoff from a portion of ADU from sheet flow over roof areas to roof down drains which is to be dispersed and directed to impervious area dispersion grassy areas located at back of ADU pool house and along the rear yard patios. All this runoff is directed to pervious area zones, grassy areas, The runoff is thence directed to grassy area inlet drains connected to the proposed 4” PVC onsite storm drain system draining to the southwest to James Drive cul-de-sac along the southwest side yard property line. The Q100P-101 has been determined to be 0.13 cfs at post- development outfall node P-01. RECOMMENDATIONS: Surface drainage from north side includes drainage of the new attached garage and residential roof drains, rear patio surface drain to landscape areas prior to being drainage into onsite storm drain system and thence to project outfall via ex SDRSD D-27 sidewalk under drain and confluence with existing public storm water in ex. James Drive, thence the storm water flows to the southeast for approx. 95’ to an existing 5’ wide curb inlet originally designed to accept the sub-division residential runoff. No down stream detrimental effects are anticipated in this public road confluence. A calculation is provided for the 5’ wide curb inlet opening showing that the inlet capacity is sufficient to receive the increase in storm water runoff from this residential development project. 2. DRAINAGE AREA: “P-102” Post development is divided into 2 basins, Basins P-101, P-102. Basin P-102 is the largest basin draining to James Drive and includes the southwesterly driveway, approximately ¾ of the residence footprint, ¾ of the Adu footprint, the southeasterly side yard and most of the rear yard,. The basin is primarily sheet flow from residence and associated patio hardscape over grassy areas to the on site proposed 4” pvc storm water drain system installed at 1.0% slope. Also a portion of this basin runoff from roof down drains from the residence and garage are also routed to grassy areas to the on site proposed 4” pvc storm water drain system installed at 1.0% slope prior to confluence with public water in James Drive@ outfall node P-02. Q100p-102 has been determined to be 0.59 cfs at post- development outfall node P-02. . Basin P-102 is separated into 2 categories first is areas draining from northeast rear yard side of the lot to the southeast and is primarily sheet flow from new residential patio areas and runoff from ADU from sheet flow over roof areas to roof down drains which is to be dispersed and directed to impervious area dispersion grassy areas located at back of ADU pool house and along the rear yard patios All this runoff is directed to pervious grassy areas prior to entering the onsite drainage system, The Runoff is thence directed to grassy area inlet drains connected to the proposed 4” PVC onsite storm drain system draining to the southwest to James Drive cul-de-sac along the southeast side yard property line to node P- 02 at the James Drive 6” curb and gutter. Secondly, runoff from a portion the same P-102 Basin, from the residence roof top and from a portion of the hardscape patio located directly in front of the Adu is collected form roof down drains and from and from the patio slotted drain and picked up directly into a separate trunk line of the onsite 4” PVC drain system this trunk line conveys to the project outfall via 2 SDRSD D-27 sidewalk under drain node P-02 at the James Drive 6” curb and gutter. RECOMMENDATIONS: Surface drainage from proposed south side includes drainage of the new residence and garage roof drains, rear patios and driveway gravity grate drains to surface of the on-site grassy area prior to being received in grassy area inlets to the proposed 4” PVC storm drain system which will outlet the treated storm water via (2) SDRSD D-27 sidewalk under drains and confluence with James Drive public water in existing 6 in curb and gutter thence, southeast in ex. James Drive 6” curb and gutter, to the southeast for approx. 95 lf to an existing 5’ wide curb inlet originally designed to accept the sub-division residential runoff. . No down stream detrimental effects are anticipated in this public road confluence. A calculation is provided for the 5’ wide curb inlet opening showing that the inlet capacity is sufficient to receive the increase in storm water runoff from this residential development project. The overall increase of 0.39 Cfs is accepted into the MS-4 city storm drain system at ex. 5’ wide curb inlet in James Drive originally designed to accept the sub-division residential runoff. No down stream detrimental effects are anticipated in this public road confluence. Refer to the Basin Summary Tables and attached Drainage Basin Maps for the runoff coefficients, Tc, and I and Q values for both Pre-development and Post-development Basins. Enlarged Soils Group Map: use soils group “B”. refer to soil group map San Diego County Hydrology Manual in appendix.