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HomeMy WebLinkAboutCDP 2019-0002; HILLSIDE DRIVE RESIDENTIAL; HYDROLOGY STUDY; 2020-02-22HYDROLOGY STUDY Smith Residence CDP 2019-0002 For Jessie Smith 447 Bougher Rd San Marcos, CA 92068 Prepared By: Ben Lund Engineering Granite Ridge Rd Escondido, CA 92026 Date: February 22, 2020 Benjamin R. Lund RCE 68849 Date TABLE OF CONTENTS 1.0 Project Description .............................................................................................................. 3 1.1 Existing Condition .................................................................................................. 3 1.2 Proposed Condition ................................................................................................. 3 1.3 Soil Characteristics ................................................................................................. 4 2.0 Rational Method Description .............................................................................................. 4 3.0 Hydrology Analysis ............................................................................................................ 5 4.0 Water Quality ...................................................................................................................... 5 Attachments: I. Vicinity Map 2. Existing Condition Hydrology Calculations & Exhibit 3. Proposed Condition Hydrology Calculations & Exhibit 2 1.0 Project Description The Smith Residence project is located on a 0.26 acre parcel in the City of Carlsbad fronting Hillside Drive which is a public street. Proposed improvements consist of a single family residence and driveway along with other associated improvements. The site is located on APN: 207-360-11, please see Attachment 1 for the Vicinity Map. 1.1 Existing Condition The existing site is approximately 0.26 acres. A 20' wide utility easement is located along the northeast property line and contains a 48" concrete storm drain pipe as well as a 1 O" sewer main (DWG 196-lA). Stormwater runoff from the site drains overland to the south, exits the site, and enters an existing 24" CMP riser (DWG 196-IA) which lugs into the 48" concrete pipe. Offsite stormwater runoff runs onto the site from APN: 207-022-10 from the north via three area drain systems that outfall close to the property line between APN s 207-022-10 and 207-022-11 but, also via small areas of overland flow. One of the area drain system drains into an existing 18" pipe (DWG 41 l-8A) which conveys emergency overflow water from a retention basin built for the James Canyon Estates (DWG 385- 7 A). Unless the retention basin fails, water normally flows into the same existing 48" concrete pipe. This pipe outfalls near the property line between APNs 207-022-10 and 207-022-11. The other two drain systems outfall near the 18" pipe outfall. The existing impervious area of the project parcel is 100%. 1.2 Proposed Condition The proposed condition will not alter the existing drainage patterns of the area. The proposed condition will extend the 18" emergency overflow pipe underneath the proposed driveway. The two offsite area drain outfalls will be replaced by inlets which will accept the small portion of overland cross-lot drainage and will connect to the existing 18" overflow pipe. Another inlet will be added and connect to the existing 18" pipe to make a total of three for redundancy and ease of maintenance. Stormwater generated by the site will be captured by area drains and conveyed, via storm drain pipes, to the ravine. Runoff in the ravine flows overland to the south, exits the site, and enters an existing 24" CMP riser (DWG 196-lA) which lugs into the existing 48" concrete pipe. Detention of runoff from the property or offsite flows is not proposed as this would cause the developed condition peak to move closer to the upstream watershed peak which would increase stormwater peak flows in downstream structures. The finish floor elevation of the proposed residence will be a minimum of 2 feet above the existing 24" CMP riser. 3 ervious area summar 3,250SF 200SF 1,500 SF Total 4,950 SF 1.3 Soil Characteristics The following soil group definitions come from Technical Release 55 (TR-55) by the United States Department of Agriculture: Group A soils have low runoff potential and high infiltration rates even when thoroughly wetted. They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of water transmission (greater than 0.30 in/hr). Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately course textures. These soils have a moderate rate of water transmission (0.15-0.30 in/hr). Group C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine texture. These soils have a low rate of water transmission (0.05-0.15 in/hr). Group D soils have high runoff potential. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr). Group D soils is conservatively assumed to size drainage structures. 2.0 Rational Method Description The rational method, as described in the 2003 San Diego County Hydrology Manual, was used to generate surface runoff flows, which were then used to size the drainage facilities. The basic equation: Q = CiA C = runoff coefficient (varies with surface) i = Intensity (in/hr) A = Area (acres) The 6 hour and 24 hour rainfall isopluvial maps are found in the 2003 San Diego County Hydrology Manual. Adjusted P6 calculations can be found on the spreadsheets in Attachments 2 and 3 along with the Rational Method routing calculations. Initial travel time calculations (T;) are based on the overland flow equation given in Figure 3-3 of the County's Hydrology Manual and is limited to the maximum overland flow length in Table 3-2 of the County's Hydrology Manual. Travel time calculations between nodes are calculated via manning' s equation or by the Kirpich equation as expressed in the County's Hydrology Manual. Travel time values are then entered 4 into the spreadsheet under T,. Confluences are done by spreadsheet and are labeled by the node number where the confluence occurs. Each outfall point is shown on the existing and proposed condition hydrology exhibits with the flow rate (Q) at that particular location. 3.0 Hydrology Analysis The table below summarizes the pre-and post-construction 100-year flows. The outfall points are shown on the Existing and Proposed Drainage Exhibits included in this report. Table 2 Summar osed stormwater runoff. A Q ac cfs 0.66 1.9 Pro osed 1 00-Yr Node #225 Outfall 0.66 1.9 The total pre-development 100 year flow is 1.9 cfs. The total post-development 100 year flow is 1.9 cfs. 4.0 Water Quality The project is a 'Standard Project' and complies with 'Standard Project' stormwater requirements. 5 References l. City of Carlsbad Engineering Design Manual by the City of Carlsbad 2. San Diego County Drainage Design Manual by the County of San Diego, May 2005. 3. San Diego County Hydrology Manual by the County of San Diego, June 2003. 6 Attachment 1 ,, \ \ \ \ SITE CITY OF \ \ PACIFIC \ OCEAN VICINITY MAP FOR SMITH RESIDENCE I I I I I I ·1 . CITY OF ~STA ROAD ·r .. :"'""'~ h CITY OF SAN MARCOS CITY OF ENCINITAS VICINI TY MAP NOT TO SCALE J .. _j MAY J, 2019 [Bs~~LUND ENGINEERING (1))2019 BEN WNO ENC/NEER/NC -27790 CRAN/TE R/OCE RO, 92026 -(760) 410-8171 -BENRLUNOfJCMAIL.COM Attachment 2 1 00-yr Storm Pre-Development Condition P6 = 2.6 P2• = 4.5 PsfP2•= 57.8% Adjusted P6 = 2.6 Calculated by BRL Date 5/25/19 Iner. Total Soil Land Used Iner. Total T; T; T; T,' Tc Tc i O=CiA Node Area Area Group Use C C C*A C*A Flow Slope min. min. min. (used) In/Hr. Q,cfs Hydraulics and Notes Description ac. ac. Path, ft % min. 100-105 0.27 0.27 D R4.3 0.52 0.52 0.14 0.14 110 20.0% 4.0 4.0 5.0 6.85 1.0 Initial Area 105-110 0.13 0.40 D R4.3 0.52 0.52 0.07 0.21 0.2 5.2 5.2 6.68 1.4 Pipe 110-115 0.26 0.66 D u 0.35 0.35 0.09 0.30 0.5 5.7 5.7 6.30 1.9 Outfall Smith-Hydro01.xlsx ·Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 30® by Autodesk, Inc. NODE 105 -110 Circular Diameter (ft) Invert Elev (ft) Slope(%) N-Value Calculations Compute by: Known Q ( cfs) Elev (ft) 0 = 1.50 = 96.00 = 3.00 = 0.024 Known Q = 1.10 -----------------------, Highlighted Depth (ft) Q (cfs) Area (sqft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Y c (ft) Top Width (ft) EGL (ft) Section 2 Reach (ft) Friday, May 3 2019 = 0.34 = 1.100 = 0.30 = 3.63 = 1.49 = 0.39 = 1.26 = 0.55 3 Pre-development Kirpich Calculations Node 110-115 T, = (11.9*L 3/AE)°-385 T1 = Time of concentration (hours) L = Watercourse Distance (miles) liE = Change in elevation along effective slooe line L (ft) = 65 liE = 5 T1 (min)= '-------' 0.5 0 15' JO' GRAPHIC SCALE t" = JO' ~ EXISTING CONDITION HYDROLOGY LEGEND ITEM BASIN FLOW PATH AREA (AC) NODE I SYMBOL 8 /100 F[BRUAR Y 22, 2020 [8)~lNJLUND ENGINEERING <!;)2020 BEN LUND ENGINEER/NC -27790 CRAN/TE RIDGE RO, 92026 -(760) 410-8171 -BENRLUND@GMAIL.COM Attachment 3 100-yr Storm Post-Development Condition Po= 2.6 P2• = 4.5 P,/P2•= 57.8% Adjusted P0 = 2.6 Calculated by BRL Date 5/25/2019 Iner. Total Soil Land Used Iner. Total T, T, T, T,' Tc T. i O=CiA Node Area Area Group Use C C C'A c•A Flow Slope min. min. min. (used) In/Hr. Q, efs Hydraulics and Notes Description ac. ac. Path, ft % min. 200-205 0.02 0.02 D R4.3 0.52 0.52 0.01 0.01 55 1.0% 7.7 7.7 7.7 5.19 0.05 Initial Area 205-225 0.05 0.07 D R43.0 0.79 0.79 0.04 0.05 0.9 8.6 8.6 4.83 0.2 Pipe 210-225 0.40 0.47 D R4.3 0.52 0.52 0.21 0.26 8.6 8.6 4.83 1.2 Add Area & Pipe 215-225 0.13 0.60 D R43.0 0.79 0.79 0.10 0.36 8.6 8.6 4.83 1.7 Pipe 220-225 0.06 0.66 D R4.3 0.52 0.52 0.03 0.39 8.6 8.6 4.83 1.9 Outfall Smith-Hydro01.xlsx ;Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. NODE 205-225 Circular Diameter (ft) Invert Elev (ft) Slope(%) N-Value Calculations Compute by: Known Q ( cfs) Elev (ft) 0 = 0.50 = 107.00 = 1.00 = 0.013 Known Q = 0.05 Highlighted Depth (ft) Q (cfs) Area (sqft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Ye (ft) Top Width (ft) EGL (ft) Saturday, May 25 2019 = 0.11 = 0.050 = 0.03 = 1.55 = 0.49 = 0.11 = 0.42 = 0.15 Section Reach (ft) 0 15' JO' GRAPHIC SCALE /"=JO' e .6 '?, ~'\ \\\ ... . \ ~· .. \ ~ '2!_5 OUTFALL // 1/ .! I o,orJ-.'·g CFS . . .· , / I // ~",1/ . •.. c,6 . .· //"✓~/ ~i // ~// \.\'°/ . / s/ ~1/ /\\✓/ ;(// //. ./('l /4• . {~/ ",,~ •.•• ('· /~ /,J /I.· 1/, . PROPOSED CONDITION YDROLOCY LEGEND ITEM BASIN FLOW PATH AREA (AC) NODE I SYMBOL /100 FEBRUARY 22, 2020 ~~[rJ]LUND ENGINEERING ©2020 BEN LUND ENC!NffR!NG -27790 GRANITE RIDGE RD, 92026 -(760) 410-8171 -BENRLUN0@GMA!LC0M