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Home My WebLink AboutTR 35337 HYDROLOGY REPORT-001 HYDROLOGY STUDY ['OR TRACT 35337 CITY Ol' LAIxE ELSINORE 1- ITXIT OH' C:AI ,l F'OlZN l A VOLUME 1 REPORT PREPARED FOR: SPYGLASS RANCH (RIVERSIDE), ASLI V, LLLP CIO PACIFIC COVES IN\ESTMENTS, LLC 23 BALBOA COVES NEWPORT BEACH, CA 92663 PREPARED BY: a 1 Engineering, Inc. 357 N. SHERIDAN STREET, SUITE 117 CORONA, CA 92880 PHONE: (951) 279 1800 FAX: (951) 279 4380 March 2013 PREPARED UNDER THE SUPERVISION OF: FARRIS N. HADDAD RCE NO. 65931 DATE Spyglasq Ranch Tract 35337 Hydrology Report TABLE OF CONTENTS FOR VOLUME 1 Report General Project I Figure 1: Vicinity Map 1 Figure 2: Site and Development Stages 2 Design Criteria 3 Scope of Report 3 Methodology 4 Pre-Developed Condition 5 Table 1: Existing Culvert Drainage Areas 6 Post-Developed Condition 7 Figure 3: Onsite Basins 9 Results and Summary Table 2: Rational Method Summary - Stage 1 10 Figure 4: Stage 1...Area Balance 11 Table 3: Rational Method Summary - Ultimate 11 Figure 5: Ultimate...Area Balance 12 Area "A" and Basin #2 13 Table 4: Basin #2 - Volume vs. Depth 13 Table 5: Basin #2 - Volume vs. Depth for WQ 14 Table 6: Basin #2 - Depth vs. Outflow 15 Table 7: Basin #2 Outlet Structure...Summary 16 Table 8: Basin #2 Detention...Route Summary 16 Table 9: Post-Developed Q...to Existing RCB Culvert 17 Area "B" 17 Area "C" (JDA Area) 17 Figure 6: Developed Areas Tributary to Tract 31593 18 Area "D" and Basin #3 19 Table 10: Unit Hydrograph Summary - 10-year Study 19 Table 11: Basin #3 - Volume vs. Depth 20 R:\2Go324\FinaI ,Ilydrology\Report\324 Titles Vol 31.do<x Spyglass Ranch Tract 35337 Hydrology Report Results and Summary (continued) Table 12: Basin #3 - Volume vs. Depth for WQ 20 Table 13: Basin #3 - Depth vs. Outflow 21 Table 14: Basin #3 Outlet Structure...Summary 22 Table 15: Basin #3 Detention...Route Summary 23 Table 16: Basin #1 - Volume vs. Depth for WQ 24 Area "E" and Basin #1 23 Area "F" and "G" 24 Area "H" 24 Area "I" 25 Area "J" 25 Area "K" 25 Area "L" (JDA Area) 26 Area "M" 26 Basin Spillways and Auxiliary Outlets 27 Conclusion 27 Hydrology Maps • Existing Condition Hydrology Map • Developed Condition Hydrology Map, Stage 1 Condition • Developed Condition Hydrology Map, Ultimate Condition Exhibits A. Unit Hydrograph Exhibits • Existing Condition Unit Hydrograph Area 9 • Developed Condition Unit Hydrograph Area "A" • Developed Condition Unit Hydrograph Area '°D" Stage 1 • Developed Condition Unit Hydrograph Area I°D" Stage 1 Tributary to Basin #3 B. Street Capacity Tables C. Catch Basin Summary Table D. Node Model Data Flow Sheets (Rational Method) • Existing Condition • Stage 1 Condition • Ultimate Condition I.: %( ) ',?24\Final ,1lydrology\Report\324 Titles Vol 01.do<x Spyglasq Ranch Tract 35337 Hydrology Report TABLE OF CONTENTS FOR VOLUME 2 (COMPUTER DISK) Appendix — Computation Output Files A. Rational Method • Existing Rational 100—Year Storm • Developed Rational 10—Year Storm Stage 1 • Developed Rational 100—Year Storm Stage 1 • Developed Rational 10—Year Storm Ultimate (Areas C, D, and Q • Developed Rational 100—Year Storm Ultimate (Areas C, D, and Q B. Unit Hydrograph Method • Existing Unit Hydrograph Area 9 (10—Year Storm, 6 and 24 hour durations) • Developed Unit Hydrograph Area "A" (100—Year Storm, 1 hour duration) • Developed Unit Hydrograph Area "D" Stage 1 (10—Year Storm, 6 and 24 hour durations) • Developed Unit Hydrograph Area "D" Stage 1 Tributary to Basin #3 (10—Year Storm, 6 and 24 hour durations) C. Basin Routing • Storm Mitigation for Basin #2 • Storm Mitigation for Basin #3 • Water Quality for Basin #2 • Water Quality for Basin #3 • Spillways for Basins #1, #2, and #3 D. Catch Basins (10—Year and 100—Year Storm Frequencies) • Area A • Area C • Area D • Area E • Camino Del Norte 1; 'G,)324\Final\hydrology\Report\324 Titles Vol 01.docx Spyglass Ranch Tract 35337 Hydrology Study Report General Project — Tract 35337, also known as "Spyglass Ranch," is a proposed development located in the City of Lake Elsinore, Riverside County, California (see Figure 1). The project is a master—planned community that consists of approximately 260 acres of mixed landuse implemented in accordance with the Spyglass Ranch Specific Plan No. 2005-02. 4 J�x Project !� L Site r. LVE JN1i�R // E)YAOPE \ Figure 1: Vicinity Map No Scale The development includes about 444 single family lots, eight acres dedicated to estate residential lots, courtyard units, multi—family units with an optional commercial site, and a six—acre public park. The project takes its primary access from Camino Del Norte, north and south of Main Street. The secondary access is from Elsinore Hills Road, which is proposed to extend to the north through Tract 31593 and connect to the existing road terminus within the Ramsgate Community in Tract 25478. H: \265324 ,,Final` hydrology\12eport\32� Report Body.doex — 1 — Spyglass Ranch Tract 35337 Hydrology Study The project is to be constructed in two stages with the majority of the development graded in Stage 1. The first stage of development is mostly independent and does not require facilities from other projects to be constructed in order to proceed. The second and final stage of the project may require such implementing facilities and likely will only occur concurrent with or after Tract 31593 is constructed (see Figure 2). EICHORN PROPERTY TRACT 31593 PM 985 I� TRACT 35337 "SPYGLASS RANCH" iSTAGE 2 0 co co Cl� S TAG E 1 H H CD Figure 2: Site and Development Stages No Scale Spyglass Ranch also supports a new water reservoir on site to serve the 1801 water pressure zone. Although the tank site is located within the second stage of grading, it must be constructed with the first stage of grading since a large number of lots will be served by it. The reservoir will also be used to support the development within Tract 31593. Because of the phased grading, the required reservoir site, and the unknown construction timing of Tract 31593, interim condition drainage patterns may be created at the time of construction of Spyglass Ranch. Consequently, the different scenarios that impact the hydrology of the site are addressed, analyzed, and compared in this report. H: \265324 ,,Final ,hydrology\Rcpor•l\324 Report Body.docx — 2 — Spyglass Ranch Tract 35337 Hydrology Study — Design Criteria — The Spyglass Ranch project is conditioned by the City of Lake Elsinore to provide a drainage study to identify storm water runoff, to show existing and proposed onsite and offsite drainage facilities, and to provide the proper capacity analyses to verify the adequacy of the proposed drainage improvements. Natural drainage courses traversing the site must be conveyed through the site, or should be collected and conveyed in such a manner that is approved by the City Engineer. All offsite drainage, if different from historic drainage patterns, shall be conveyed to a public facility, or accepted by an adjacent property owner by a letter of drainage acceptance, or conveyed to a drainage facility within an easement. Furthermore, the drainage system shall be designed to ensure that runoff from a 10—year storm event of 6 hour or of 24 hour durations under the developed condition is equal to or less than the runoff under the existing conditions of the same storm frequency. Both the 6 hour and the 24 hour storm durations shall be analyzed to determine the onsite detention basin capacities necessary to accomplish the desired results. Onsite peak flow rates for the 10—year storm event are to be managed at or below the curb line; peak flow rates for the 100—year storm event are to be managed within the right—of—way (R/W) limits. If these limits are exceeded, underground storm drain facilities must be provided to lower the water surface levels in the roadway to or below the maximum indicated levels. Water quality treatment and conveyance is to be provided in accordance with NPDES requirements to be implemented per the Regional Water Quality Control Board standards and guidelines for the Santa Ana Watershed. The required water quality treatment volumes and basin capacities are determined per the City's WQMP handbook (worksheets included in this report) and are to be consistent with the approved Spyglass Ranch Preliminary WQMP. Water quality basins must provide an outlet designed to retain a minimum of half of the water quality design volume for a minimum of 24 hours and the remaining water quality design volume for a minimum of 48 hours, but no longer than 72 hours. Overall, the project site must be designed to safely convey the 100—Year storm event through the site should failure of the underground storm drain system occur. Any further criteria for this report is provided by and based on the RCFCWCD hydrology manual. — Scope of Report — The purpose of this study is to calculate the storm water runoff associated with the proposed development as necessary to satisfy the City's conditions and requirements for the drainage study. Results from this study will be used to (1) provide the design flow rates that the storm drain system is designed to manage, and (2) analyze the increase runoff due to development and determine the amount of mitigation where necessary. The results from this study will be used to size and/or confirm H: \265324\Final\llydrology\RcporL' 324 Report Body.doex — 3 — Spyglass Ranch Tract 35337 Hydrology Study the storm drain pipes, catch basins, onsite detention basin volumes and hydraulic performance, detention basin outflow structures (water quality control and storm mitigation), and the street flood capacity. This study considers the conveyance of all the local onsite and tributary offsite drainage flows for both the ultimate and interim conditions. This study includes the hydraulic analysis and design of the culvert system being used in the post—developed condition that is located along the project frontage on Camino Del Norte. The proposed development is considered to have no adverse hydraulic impacts on the downstream conveyance facilities located along the westerly side of the Freeway that drain northerly. Consequently, analysis of these downstream facilities is not necessary and is therefore excluded from this study. The study includes a general evaluation of the Wasson Canyon Basin, a Municipal Separate Storm Sewer System ("MS4") facility, which is located downstream and approximately 800 feet from the project's westerly boundary. The Basin is owned and operated by the Riverside County Flood Control District (RCFCD) and is to serve as an ultimate discharge point for a large part of the project's drainage runoff. The purpose of the evaluation is to confirm that the Basin is not adversely impacted by the proposed development flows. The Basin Plan referenced in this study is the Wasson Canyon Channel Stage I RCFCD Project No. 3-0-180. — Methodology — Rational method hydrology is implemented to calculate the 100—year and 10—year storm frequency peak flow rates. Drainage areas are determined and defined using ridgeline boundaries and "link—node" streams. The rational calculations are performed by Rational Method Riverside County ("RRIV") provided in the Civil Design Software suite, developed by Joseph E. Bondiman & Associates and recommended by RCFCWCD. Rainfall, loss rates, and other such data that is pertinent to the rational method calculations are determined by "RRIV" and summarized within the output files provided herein. By combining the "link—node" rational method in the 'RRIV" program with street depth and catch basin capture calculations, the storm drain pipes and catch basin sizes are determined. These values dictate the placement and sizing of the underground drainage facilities based upon the street capacity. This method makes use of "RRIV" for primarily three values: peak flow rates, time of concentration, and accumulated drainage area. Values generated by "RRIV" that are neglected and may be found more accurately, as determined in the hydraulic calculations, include depth of street flow, street capacity calculations, and catch basin capture calculations. Synthetic unit hydrograph modeling is used in accordance with City and RCFCWCD requirements and guidelines to study the appropriate storm return frequencies and durations to be mitigated. Mitigation for the necessary conditions will be achieved thorough detention basins and the use of a control outlet valve structure. The software employed to compute the unit hydrographs and basin routing calculations are contained within the Civil H: \265324\Final`\llydrology\Rcport\324 Report Body.docx — 4 — Spyglass Ranch Tract 35337 Hydrology Study Design Software suite and recommended by RCFCWCD. Rainfall, loss rates, AMC requirements, and other such data that is pertinent to the development of the unit hydrographs are based upon Increased Runoff Criteria typically required by RCFCWCD. — Pre—Developed Condition — By in large, the soil type for the majority of this site has a high runoff potential, as designated by the U.S. Soils Conservation Service (SCS) as Soil Groups C and D. These areas are characterized as having a low capacity to transmit water, thereby resulting in a slow to very slow rate of infiltration, and a relatively high volume of runoff. There are, however, some minor areas that are characterized as having moderate infiltration rates, designated as SCS Soil Group B (ref. RCFCD Hydrology Manual Plate C-1.41). The appropriate ratio of each soil group is used in the existing condition model of this study. Another factor that adds to the high potential for storm runoff due to the existing soil type is that the site also has poor ground cover. For purposes of these study computations, poor soil cover is basically defined by SCS as a watershed having less than fifty—percent of its ground surface covered by tree canopy and brush. Another factor that will generate a high rate of runoff in the existing condition is the significant relief across the site. Generally, the lay of the land flows in a south to southwesterly direction towards Lake Elsinore, which sits just over one mile downstream of the subject tract. The highest elevation within the site is approximately 1800 feet MSL and the lowest elevation is approximately 1300 feet MSL. The existing terrain is mountainous with significant hill and valley formations. Storm runoff from the site takes several different local paths from the project site prior to reaching the Lake, the ultimate discharge point. A number of ridgelines divide the site into distinct drainage areas that create flow paths in all directions. Because of this, there are many drainage courses that outlet across the boundary on all sides of the project. Yet, since the site is relatively elevated within its vicinity, there are essentially no substantial offsite flows that are tributary to the site. Generally speaking, the site's watershed boundary nearly matches the project boundary with flow patterns that run from onsite to offsite. However, there are three areas that contain a drainage course that has multiple project boundary crossings, flowing offsite to onsite and vice versa. Referencing the Existing Condition Hydrology Map, these areas are identified as Areas 2, 4, and 12. These drainage areas do not raise a great deal of concern since the offsite contribution within these sub—areas is relatively minimal. These drainage areas are discussed further in their post— developed condition under the following section of this report. Although the majority of the drainage areas are treated in a standard manner as they relate to the existing and developed conditions, there are three edge conditions that are worthy to note. The first is the frontage along Camino Del Norte, the second is the far west boundary that is adjacent to Parcel Map (PM) 30985, and the third is the north boundary H: \265324\Final \llydrology\Rcpor•l\324 Report Body.docx — 5 — Spyglass Ranch Tract 35337 Hydrology Study that is adjacent to Tract 31593, also referred to herein as "South Shore." Each of these areas will be addressed throughout the report as they relate to the post—developed conditions under the ultimate condition, interim condition, or both scenarios when applicable. Following is a brief description of these three edge conditions in their existing states. Firstly, to the southwest, there are five identifiable drainage areas that are intercepted by existing culverts located along the frontage road, Camino Del Norte. The series of culverts along Camino Del Norte are maintained by the City and are designed to capture flows generated from the site, then convey them under the I-15 Freeway, then along the westerly side of the I-15 Freeway towards the Wasson Canyon Basin, and then into the Lake Elsinore Channel. The areas tributary to the existing culverts are identified in the Existing Condition Hydrology Map as Areas 12 through 16, inclusive. Table 1 lists each drainage area and the culvert it discharges into. Table 1: Existing Culvert Drainage Areas Drainage Area Designation Existing Culvert Description Node 12 54" CSP 1213 13 36" ACP 1.301 18" AC P 14 30" ACP 1403 15 18" CSP 1502 16 30" ACP 1603 Notes: 1. Node numbers reference the Existing Condition Hydrology Map. The 54" culvert inlet is a concrete headwall structure located at an existing drainage course near an existing access road. The other smaller culvert inlets are grated inlets generally located along the toe of slope at the project's frontage that are designed to intercept runoff from the site that drains off of the road slopes. The 36" and 18" culverts designated as nodes 1305 and 1308, respectively, confluence just downstream of their inlets at node 1.031, as reflected in Table 1. Secondly, there is an existing 61x5' RCB culvert located in Camino Del Norte approximately 700 feet northerly of the Spyglass Ranch west project boundary. The inlet to the RCB is a concrete headwall structure that is located at the frontage of the downstream property, PM 30985, and is maintained by the City. This RCB culvert extends beneath Camino Del Norte and the I-15 Freeway and connects to a 54" reinforced concrete pipe (RCP) near the Wasson Canyon Channel at Collier Avenue, just upstream of the Wasson Canyon Basin. PM 30985 indicates an approved design flow rate for the RCB culvert of 168 cfs at the inlet within its property, and 185 cfs downstream of the two minor catch basin lateral connections that occur in Camino Del Norte just downstream of the inlet. The majority of this flow is generated by an existing drainage course that enters PM 30985 from its east boundary through the Spyglass Ranch property. The drainage area within Spyglass Ranch that is tributary to this drainage course is identified H: \265324` Final`\llydrology\Report\32a Report Body.docx — 6 — Spyglass Ranch Tract 35337 Hydrology Study hI ^ LJ as Area 2. PM 30985 shows that it accepts an approved flow rate from Spyglass Ranch at their common boundary of 128 cfs. This runoff is depicted per the PM 30985 improvement plans to be intercepted in a 71x3' RCB headwall inlet structure that is located at the common property line. Thirdly, there is a drainage area whose drainage course crosses at multiple locations the portion of the north boundary adjacent to the South Shore development. The area tributary to this drainage course is identified as Area 4. It can be observed that the primary drainage course in Area 4 originates within Spyglass Ranch (at node 401), then crosses the north boundary into South Shore (at node 402), then re-enters Spyglass Ranch (near node 403), and finally crosses the north boundary a third time into South Shore (at node 406) before confluencing with another drainage course (at node 407) within the South Shore property that drains westerly. It is noteworthy that a special condition is presented by this drainage area that will be further addressed under the Post-Developed Section of this report. Post-Developed Condition - Stage 1 and Ultimate Condition Scenarios This study takes under consideration two different construction scenarios for the Spyglass Ranch development. Spyglass Ranch is proposed to be graded in two stages, as depicted in Figure 2. Stage 1 is comprised of the first five of the seven tract phases (i.e. 35337-1, -2, -3, -4, and -5) and includes the vast majority of the single family residential lots along with the park site and the higher-density development parcels. Since construction of Stage 1 can be completed mostly independent of South Shore commencing work, there is an interim condition construction scenario that is plausible, and thus used as one of the two overall post-developed models evaluated in this study. This interim condition occurs after the Stage 1 grading is complete and South Shore is not yet constructed. At this stage, there is significant offsite grading that is necessary for Spyglass Ranch in order to complete the road and lot construction in the vicinity of its common boundary with South Shore. This condition is called "Stage 1" for purposes of this report. It is noteworthy that Stage 1 also includes the construction of the water tank site and the appropriate access road to it. The "Developed Condition Hydrology Map - Stage 1" depicts this lot configuration and grading scenario. Stage 2 is comprised of the last two of the seven tract phases (i.e. 35337-6, -F) that includes single family residential lots and several larger estate residential lots. Since construction of Stage 2 is dependent on South Shore for access, it is plausible that Stage 2 will be constructed either concurrent with or after South Shore develops. Thus, the Stage 2 grading scenario is evaluated under the ultimate (i.e. built out) condition for both projects and used as the second of the two overall post-developed models evaluated in this study. This condition occurs after the Stage 2 grading is complete and South Shore is constructed in its entirety. At this stage, secondary access is available for the Spyglass Ranch final phases at its common boundary with South Shore. This condition is called "Ultimate" for H: \265324\Final`\llydrology\Report\32a Report Body.docx - 7 - Spyglass Ranch Tract 35337 Hydrology Study purposes of this report. It is noteworthy that the ultimate condition does not consider any interim offsite grading into the South Shore project. The "Developed Condition Hydrology Map - Ultimate Condition" depicts this lot configuration and grading scenario. It is important to note that three of the thirteen developed drainage areas presented in this study are impacted differently under each of the Stage 1 and Ultimate scenarios. Accordingly, two sets of computations are provided for the rational analysis for these three areas - one for the Stage 1 condition and the other for the Ultimate condition. The other ten drainage areas are essentially the same under either scenario. Basins Spyglass Ranch supports three drainage basins that serve as either water quality basins, storm mitigation facilities, or both. See "Figure 3: Onsite Basins." The basins are designed to be in compliance with RCFCD standards and guidelines and are briefly described below. Detail basin routing computations and water quality design worksheets can be found in the Appendix of this report and in the Spyglass Ranch Water Quality Management Plan (WQMP). Basin #1 is an off-line, single purpose water quality infiltration basin. The primary basin area plus the forebay area have an overall volume capacity of about 100,600 cubic feet, or 2.3 acre-feet. The basin is designed to treat about 53 acres of development. A bifurcation structure at the storm drain main line will divert only the required water quality volume from the main line and into the basin. Storm flows are designed to bypass the basin and discharge directly into the existing culvert located in Camino Del Norte. A relief underdrain and emergency overspill structure is provided for the basin in case of minor storm flow escape into the basin from the mainline and in case of infiltration failure. Basin #2 is an in-line, dual purpose extended detention basin. The primary basin area plus the forebay area have an overall volume capacity of about 252,000 cubic feet, or 5.8 acre-feet. The basin is designed to mitigate and treat about 69 acres of development. All tributary storm flows from the storm drain system will be discharged into the basin. The basin is designed to treat the first flush flows for water quality and mitigate the higher storm flows with the use of a control basin outlet valve. The basin outlet pipe located in Camino Del Norte will connect and discharge the mitigated flows into the existing RCB culvert located about 700 feet downstream of the basin. The basin is designed to mitigate the higher storm flows such that the total post-developed flow rate generated from Spyglass Ranch that enters the existing RCB culvert does not exceed the approved flow rate in the existing RCB culvert. An emergency overspill structure is provided for the basin in case of an outlet structure failure. Basin #3 is an in-line, dual purpose extended detention basin. The primary basin area plus the forebay area have an overall volume capacity of about 103,000 cubic feet, or 2.4 acre-feet. The basin is designed to mitigate and treat 28 acres of development. All tributary storm flows from H: \265324`•Final` hydrology\12eport\32� Report 13ody.doex — 8 — Spyglass Ranch Tract 35337 Hydrology Study o Basin #2 Basin #3 Basin #1 Figure 3: Onsite Basins No Scale the storm drain system are designed to discharge into the basin. The basin is designed to treat the first flush flows for water quality and mitigate the higher storm flows with the use of a control basin outlet valve. The basin outlet pipe will discharge the mitigated storm flows into the existing drainage course on the adjacent downstream property. An emergency overspill structure is provided for the basin in case of an outlet structure failure. R: \65324\Final\llydrology\Report\324 Report Body.docx — 9 — Spyglass Ranch Tract 35337 Hydrology Study A Table 3: Rational Method Summary - Ultimate Condition Variable Areas D.18 & D.19 6, 7, 8 9.7 20.9 4.11 6.60 L 5 50.0 31.0 18.09 10.55 Sub-Total: 94.46 100.52 Similar Total Areas from Table 1: 200.22 193.32 Totals: 294.68 293.84 Notes: 1. Existing point assumed at Node 407 for purposes of comparison. 2. Developed Q shown for purposes of comparison equals summation of Q at Nodes 0.305, 0.306, 334.1, 336.1, 346, and 347.1. It may be observed that there is a slight difference between the total developed condition drainage area and the total existing condition drainage area (i.e. 294.76 vs. 293.84 acres). The minor difference is attributed primarily to the proposed offsite grading slope areas and is accounted for in Figure 5. Exist. Drainage------- �` f0.17ac Dev. Boundary +0.34ac Dev. +D.71ac Exist. +0.23ac Dev. /? // +6.150c Exist. +0.02ac Dev. +0.21ac Exist. TOTAL Dev. (Ultimate) drainage Area: TOTAL Ex. drainage Area: 294,76ac 293.84ac I" t1.38ac +0.26ac +0.97oc Dev +0.71ac +0.28ac f0.21ac +1.27ac I +6.15ac +0.29ac +5.54ac 303.21 ac +0.17ac +0.23ac +0.34ac Exist. Drainage f 0.97ac Boundary Developed Drainage Boundary +0.02ac I +0.26ac Dev. +1.27 303.21ac � ac Dev. +5.54ac Dev. I 77 \ +0.29oc Dev. +1.38ac Exist.--, \� i +0.28ac Dev �J Figure 5: Ultimate (Ult) Developed vs. Existing Drainage Area Balance No Scale R: \265324 F'inal`,Hydrology\Rcport. 324 Report Hody.docx - 12 - Spyglass Ranch Tract 35337 Hydrology Study It may be observed that there is a slight difference between the total developed condition drainage area and the total existing condition drainage area (i.e. 313.91 vs. 307.65 acres). The minor difference is attributed primarily to the proposed offsite grading slope areas and is accounted for in Figure 4. TOTAL Dev. (Stage 7) drainage Area: TOTAL Ex. drainage Area: 373.970c 307.65ac +1.38aC +0.26ac +0.28ac 315.29ac +1.27ac +0.29ac +5.54aC Exist. & Dev. (s9) Drofnoge Boundary 315.29ac I Exist. Drainage Developed Drainage Boundary Boundary difference I I +0.26ac Dev. � +1.27ac Dev, +5.54ac Dev. I +0.29oc Dev. +1.38ac Exist. \�\ / +0.28ac Dev. Figure 4: Stage 1 (S1) Developed vs. Existing Drainage Area Balance No Scale Table 3 identifies only those drainage areas that are different in the Ultimate condition. All other drainage areas remain the same from the Stage 1 to Ultimate condition scenarios. Table 3: Rational Method Summary - Ultimate Condition Variable Areas Developed Dev Ex. Condition Area Equiv. Existing Developed Existing Total Total (Ultimate) Condition Area Q(100yr) Q(100yr) Area Area (Ac) (ac) C 1 41 1 133.521 155.0 1 44.67 1 53.56 D 19 1 69.7 86.1 27.59 29.81 R: \265324\Final\llydrology\Report\324 Report Body.doex Spyglass Ranch Tract 35337 Hydrology Study Results and Summary This study divides and models the site into sixteen existing condition drainage areas and thirteen developed condition drainage areas. The existing areas are designated as Areas 1 through 16, and the developed areas are designated as Areas "A" through "M," as depicted in both the Stage 1 and Ultimate Developed Condition Hydrology Maps. Note that for ease of reference, the drainage area designations shown on the all the hydrology maps and exhibits represent the same drainage areas (for example, existing Area 9 as modeled in the rational method analysis is the same existing Area 9 modeled in the existing unit hydrograph analysis). As already discussed, the rational method analysis was performed on both the Stage 1 and Ultimate condition scenarios. The node model data flow sheets for each analysis, including the existing condition, are provided for reference in the Exhibits section of this report. The flow rates resulting from the rational method analysis are used in determining the volume street flow, catch basin sizing and locations, and the storm drain pipe necessary to achieve the design criteria. Street capacity and catch basin design summary tables are provided in the Exhibits section of this report. Table 2 is provided to summarize the Stage 1 condition results of the rational method study. The table presents only the peak 100-Year flow rate values for purposes of comparison where appropriate. Discrepancies between Developed and Existing conditions indicated in the table, as well as other hydrological concerns, are discussed in the sections following. Table 2: Rational Method Summary - Stage 1 Condition Developed Developed Existing Condition Area Equiv. Existing Developed Existing Total Total (Stage 1) Condition Area Q(100yr) Q(100yr) Area (Ac) Area (ac) A 1 172.1 14.6 70.37 4.72 B 2 45.6 138.1 18.81 50.04 C 4 180.8 193.6 65.71 67.37 D 9 73.6 86.1 30.66 29.81 D.18 & D.19 6, 7, 8 12.2 20.9 4.68 6.60 E 12 134.0 199.4 53.18 71.12 F-G 13 55.3 64.1 27.77 21.64 H 14 32.5 39.6 10.00 12.56 I 15 11.1 7.3 2.85 2.04 J 16 34.3 29.2 10.82 9.73 K 3 5.4 36.0 2.15 11.00 L 5 28.3 31.0 12.56 W.55 M 10, 11 14.0 36.2 4.35 10.47 Totals 313.91 307.65 H: \265324\Final\llydrology\Report\324 Report Body.docx - 10 - Spyglass Ranch Tract 35337 Hydrology Study M 5. Main outlet Q used to confirm WSE inside baffle chamber. Q not used in determining the route rating curve. Tables 7 summarizes the outlet structure design for Basin #2. Table 7: Basin #2 Outlet Structure Design Summary Outlet Structure Openings Number Invert orifices Dia. or Invert elev. or W (in) Area (sf) Elev. above Remark H (in) (MSL) bottom (ft) Stage 1 4 1.5 0.049 1292.00 2.74 At baffle wall Stage 2 5 12 3.927 1295.85 6.15 At baffle wall Stage 3 4 8 1.396 1297.18 7.65 At baffle wall Main Outlet 1.0 48 12.566 1291.20 0 At headwall Baffle Wall Weir (Stage 4) Invert Weir elev. Crest L (FT) Above Elev. bottom (MSL) (ft) 8.0 9.55 1298.75 As already discussed, there is no storm mitigation requirement at this location since the intended outlet is the Wasson Canyon Basin, an 11MS4" improved drainage facility owned and operated by RCFCD. However, in this case, since the goal is to match the approved 100-Year flows in the existing RCB culvert, the basin outlet is designed to mitigate the 100-Year storm flows. Table 8 provides a summary of the basin detention performance. Table 8: Basin #2 Detention Basin Route Summary Duration QPK3 (cfs) QPK (cfs) Max Water QPK (cfs) UHA into UHA out of Depth in (hr) basin basin reduction Basin (ft) 1 168.5 72.5 96.0 7.6 Notes: 1. UHA = unit hydrograph for Area "A" 2. Q is 100-Year Strom Frequency. 3. QPK for UHA is calibrated to match the rational method Q. H: \265324 Final \ilydrology\Report\324 Report 13ody.doex - 16 - Spyglass Ranch Tract 35337 Hydrology Study M designed to provide storm and water quality mitigation. The flow rate is given by "Q" in cubic-feet-per-second (cfs). Table 6: Basin #2_ - Depth vs. Outflow WS Stage 1 Stage 2 Stage 3 Stage 4 Cumulative Main Depth Elevation Q (cfs)' Q (cfs)2 Q (cfs)3 Q (cfs)4 Outflow Q Outlet Q (cfs) (cfs)5 8.00 1300.00 0.74 42.37 12.42 36.61 92.13 179.49 7.50 1299.50 0.71 39.74 11.26 17.01 68.73 174.32 7.00 1299.00 0.69 36.91 9.98 3.27 50.85 168.99 6.50 1298.50 0.66 33.86 8.50 0.00 43.02 163.48 6.00 1298.00 0.64 30.50 6.70 0.00 37.83 157.78 5.50 1297.50 0.61 26.72 4.18 0.00 31.51 151.87 5.00 1297.00 0.58 22.30 0.00 0.00 22.89 145.72 4.50 1296.50 0.55 16.77 0.00 0.00 17.32 139.30 4.00 1296.00 0.52 8.06 0.00 0.00 8.58 132.56 3.50 1295.50 0.49 0.00 0.00 0.00 0.49 125.47 3.00 1295.00 0.45 0.00 0.00 0.00 0.45 117.95 2.66 1294.66 0.42 0.00 0.00 0.00 0.42 112.55 2.33 1294.33 0.40 0.00 0.00 0.00 0.40 107.05 2.00 1294.00 0.37 0.00 0.00 0.00 0.37 101.25 1.66 1293.66 0.33 0.00 0.00 0.00 0.33 94.90 1.33 1293.33 0.30 0.00 0.00 0.00 0.30 88.31 1.00 1293.00 0.26 0.00 0.00 0.00 0.26 81.18 0.66 1292.66 0.21 0.00 0.00 0.00 0.21 73.11 0.33 1292.33 0.15 0.00 0.00 0.00 0.15 64.32 Notes: 1. (4) 1.5 in. diameter orifice in exterior baffle wall, invert=1291.94. 2. (5) 12 in. diameter orifice in exterior baffle wall, invert=1295.35. 3. (4) 8 in. diameter orifice in exterior baffle wall, invert=1296.85. 4. 8 ft. wide baffle wall, TW=1298.75. H: \265324\Final \llydrology\Rcpor•l\324 Report Body.doex - 15 - Spyglass Ranch Tract 35337 Hydrology Study Table A- _Basin. ##2 - Vo-lume V-s Depth 1296.50 41400 20200 117678 2.7015 4.50 1296.00 39400 19250 97478 2.2378 4.00 1295.50 37600 17475 78228 1.7959 3.50 1295.00 32300 10478 60753 1.3947 3.00 1294.66 31200 9983 50276 1.1542 2.66 1294.33 29300 9207 40293 0.9250 2.33 1294.00 26500 8168 31086 0.7136 2.00 1293.66 23000 6947 22919 0.5261 1.66 1293.33 19100 5693 15972 0.3667 1.33 1293.00 15400 4439 10280 0.2360 1.00 1292.66 11500 3284 5841 0.1341 0.66 1292.33 8400 2558 2558 0.0587 0.33 1292.00 7100 0 0 0.0000 0.00 Table 5: Basin #2 - Volume Vs. Depth for Water Quality' Contour Contour Volume Total Total Volume Basin Elevation Area (CF) Volume (Acre-FT) Depth (SF) (C F) (FT) 1296.00 39400 19250 97478 2.2378 4.00 1295.50 37600 17475 78228 1.7959 3.50 1295.00 32300 10478 60753 1.3947 3.00 1294.66 31200 9983 50276 1.1542 2.66 1294.33 29300 9207 40293 0.9250 2.33 1294.00 26500 8168 31086 0.7136 2.00 1293.66 23000 6947 22919 0.5261 1.66 1293.33 19100 5693 15972 0.3667 1.33 1293.00 15400 4439 10280 0.2360 1.00 1292.66 11500 3284 5841 0.1341 0.66 1292.33 8400 2558 2558 0.0587 0.33 1292.00 7100 0 0 0.0000 0.00 VBMP = 72890 1.6733 VBMP Water Depth = 3.4 Notes: 1. Volumes shown use the upper and bottom stages of basin. Forebay volume is not included in the computations. Table 6 provides a summary of Basin ##2 Depth vs. Outflow, as utilized in the routing analysis. Note that the basin has an outlet structure that is I.: 67) ;' I I'innl ,lkdr'ology ,Kopor'I 1 I,rpni l Hnd\.dn< a - 14 - Spyglass Ranch Tract 35337 Hydrology Study The following sections provide a brief description of each drainage area and the drainage basins along with the general results and computation summaries. The hydrology computations and output files are provided in the Appendix of this report. Area "A" and Basin #2 Area "A" is a major drainage area in the post-developed condition that is comprised of about half of the west side of the site. The closest comparable drainage area in the pre-developed, or existing condition based upon the drainage outlet is Area 1. One may observe that Area 1 is much smaller than Area "A". This is due to the proposed onsite grading that causes a large portion of the existing drainage area that is tributary to the adjacent downstream property to the west, PM 30985, to be redirected to the Spyglass Ranch drainage basin, which is near the existing Area 1 outlet point. This localized diversion is not an issue for three reasons: (1) the onsite basin is designed to detain the increased runoff from the drainage area, (2) the reduced runoff received to PM 30985 does not create a potential adverse condition, and (3) the runoff from this area is discharged to the Wasson Canyon Basin, a publically owned drainage facility. Area "A" is completely tributary to Basin #2. The higher storm runoff that enters the basin from this drainage area is mitigated at a ratio of about 0.6 to 1 - in other words the basin can detain about 60% of the volumetric flow rate delivered to it. The runoff from this area will drain through the detention basin and into the existing 61x5' RCB culvert through the basin's outlet pipe located in Camino Del Norte. The basin is sized to retard the necessary flow such that the approved overall total flow rate of the existing RCB culvert is not exceeded. Basin #2 is also designed as a water quality facility that will treat the first flush flows from the entire tributary area as required by NPDES guidelines. Table 4 provides a summary of Basin #2 Volume vs. Depth relationship, as utilized in the routing analysis. Table 5 provides a similar summary of Basin #2 Volume vs. Depth relationship, except as related to the required water quality treatment. Table 4: Basin #2 - Volume Vs. Depth Contour Contour Volume Total Total Basin Elevation Area (CF) Volume Volume Depth (SF) (CF) (Acre-FT) (FT) 1300.00 55600 27275 287028 6.5893 8.00 1299.50 53500 26225 259753 5.9631 7.50 1299.00 51400 25200 233528 5.3611 7.00 1298.50 49400 24175 208328 4.7826 6.50 1298.00 47300 23150 184153 4.2276 6.00 1297.50 45300 22150 161003 3.6961 E5.50 1297.00 43300 21175 138853 3.1876 5.00 H: \265324 Jinal\llydrology\Rcporl\324 Report Body.docx - 13 - Spyglass Ranch Tract 35337 Hydrology Study \`y required for this sub—area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Basin Spillways and Auxiliary Outlets In the event that any of the basins do not drain properly, each basin is equipped with an emergency spillway. The concrete lined spillway for Basin #1, an infiltration basin, is located on the easterly side of the basin adjacent to Elsinore Hills Road. The spillway is set just above the design water surface elevation and is sized to manage the maximum flowrate that is designed to bifurcate into the basin plus any additional runoff that is directly tributary to the basin. In addition to the spillway, an emergency outlet pipe with a shear gate is provided near the basin bottom in the event that standing water would need to be drained for any reason. The concrete lined spillway for Basin #2, a dual purpose extended detention basin, is located on the westerly side of the basin adjacent to Camino Del Norte. The spillway is set above the outlet structure baffle wall weir and is sized to manage the maximum design flowrate tributary to the basin. The outlet structure provides a shear gate clean out in the event that standing water would need to be drained for any reason. The concrete lined spillway for Basin #3, a dual purpose extended detention basin, is located on the southerly side of the basin adjacent to the south tract boundary. The spillway is set above the outlet structure baffle wall weir and is sized to manage the maximum design flowrate tributary to the basin. The outlet structure provides a shear gate clean out in the event that standing water would need to be drained for any reason. The critical hydraulic routing calculations for the spillways are provided in the Appendix of this report. — Conclusion — The projected flows that will be discharged to the existing properties and facilities downstream of the proposed development are permissible within the criteria and specifications indicated in this study and satisfy the City conditions of approval for increased runoff criteria. All tributary offsite flows are either mitigated to match the historic flows, or conveyed to a public drainage facility, or accepted by the receiving property via a joint development agreement (drainage acceptance agreement). The three onsite basins are designed to provide the necessary water quality treatment to be in compliance with NPDES guidelines and regulations. Two of the three onsite basins are also designed for storm mitigation based upon the increased runoff criteria for the 10—Year storm frequency at the 6 hour and 24 hour storm durations. The proposed streets and storm drain system provide sufficient capacity to manage all 10—year and 100—year flows at their required limits per the Conditions of Approval. Overall, the entire site is designed to safely convey and manage the runoff from the 100—year storm frequency. H: \265324\Final\llydro1ogy\Rcporl\324 Report Body.docx — 27 — Spyglass Ranch Tract 35337 Hydrology Study developed condition peak flow rate of Area 3. It follows, consequently, that no storm mitigation is required for this drainage area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Area "L" (JDA Area Area "L" is a drainage area in the post—developed condition that is tributary to the adjacent downstream property to the north, namely South Shore (see Figure 6). Under the Stage 1 condition, the area is comprised largely of natural area with manufactured slope area. Under the Ultimate condition, the area is comprised of one—quarter acre residential and estate lot residential developments. The comparable drainage area in the pre— developed, or existing condition is Area 5. Since, Area "L" is impacted differently under each of the Stage 1 and Ultimate scenarios, this study evaluates the drainage area under both scenarios in order to determine the more critical condition. In short, the Stage 1 developed condition will generate a lower tributary area than the Ultimate developed condition will generate at the drainage area's outlet point. Both of these conditions exceed the tributary area in the existing condition. Under the Stage 1 scenario, the drainage course of Area "L" is released at the north Spyglass Ranch boundary at the existing drainage course that continues northerly onto the South Shore property. Under the Ultimate condition, the developed condition storm flows from this drainage area will connect to the South Shore storm drain system to be conveyed to the South Shore drainage basin. Due to topographical and other constraints, Area "L" is resolved in the JDA by a drainage acceptance agreement on the part of South Shore and to the benefit of Spyglass Ranch. In other words, it is mutually agreed upon that there is no requirement for Spyglass Ranch to mitigate for any incremental increase in runoff due to development that may enter the South Shore property as a result of Spyglass Ranch developing its property. The JDA stipulates that South Shore will accept all of the tributary developed area from Spyglass Ranch. South Shore will convey and provide the necessary water quality treatment to these storm flows prior to the waters being discharged to Wasson Canyon Creek. Area "M" Area ''M" is a drainage area located along a portion of the Spyglass Ranch south property line in the post—developed condition that is tributary to the adjacent downstream properties to the south. For the most part, this drainage area is comprised of manufactured slope area. The comparable drainage areas in the pre—developed, or existing condition are Areas 10 and 11. Area "M" developed condition drainage area produces a lower tributary drainage area when combined and compared to the correlating existing condition drainage areas. The rational analysis indicates that the total developed condition peak flow rate of Sub—Area "M" is less than half that of the total pre—developed condition peak flow rate of Areas 10 and 11. It follows, consequently, that no storm mitigation is H: \265324`•Final` hydrology\12eport\32� Report Body.doex — 26 — Spyglass Ranch Tract 35337 Hydrology Study the low flows originate on natural ground, water quality treatment is not necessary for this area. The higher storm flows are designed to discharge into the existing 30" culvert located in Camino Del Norte. The rational analysis indicates that the developed condition peak flow rate of Areas "H" is less than the total pre—developed condition peak flow rate of Area 14. It follows, consequently, that the capacity of the existing culvert will not be exceeded and therefore no storm mitigation is required for this area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Area "I" Area "I" is a minor drainage area in the post—developed condition that is comprised of less than three acres of roadway and manufactured slope area. The comparable drainage area in the pre—developed, or existing condition is Area 15, which similarly is roadway and manufactured slope area. The low flows from this area are designed to be treated within the catch basin via a catch basin filter or other similar water quality treatment device. The higher storm flows are designed to discharge into the existing 18" culvert located in Camino Del Norte. The rational analysis indicates that the developed condition peak flow rate of Area "I" is well within the capacity of the existing culvert and therefore no storm mitigation is required for this area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Area '°J" Area "J" is a drainage area in the post—developed condition that is primarily comprised of natural area. The comparable drainage area in the pre—developed, or existing condition is Area 16. Since the vast majority of the low flows originate on natural ground, water quality treatment is not necessary for this area. The higher storm flows are designed to discharge into the existing 30" culvert located in Camino Del Norte. The rational analysis indicates that the developed condition peak flow rate of Area "J" is well within the capacity of the existing culvert and therefore no storm mitigation is required for this area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Area "K" Area "K" is a minor drainage area in the post—developed condition that is primarily comprised of manufactured slope area near the north property line of Spyglass Ranch. The comparable drainage area in the pre— developed, or existing condition is Area 3. Since the developed area is less than one acre, water quality treatment is not necessary for this area. Storm runoff from Area "K' will drain onto the adjacent downstream property to the north, referred to as the Eichorn Property for purposes of this report. In the developed condition, the area tributary to the Eichorn Property is much smaller when compared to the correlating existing condition drainage area. The rational analysis indicates that the total developed condition peak flow rate of Area °°K" is less than the total pre— R: \265324\Final\llydro1ogy\Rcporl\323 Report Body.docx — 25 — Spyglass Ranch Tract 35337 Hydrology Study area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Table 16 provides a summary of Basin #1 Volume vs. Depth relationship, as related to the required water quality treatment. Table 16: Basin #1 — Volume Vs. Depth for Water Quality Contour Contour Volume Total Total Volume Basin Elevation Area (CF) Volume (Acre—FT) Depth (SF) (CF) (FT) 1400.00 36800 36200 176600 4.0542 4.50 1399.50 35600 34950 140400 3.2231 4.00 1399.00 34300 33100 105450 2.4208 3.50 1398.00 31900 30700 72350 1.6609 2.50 1397.00 29500 28350 41650 0.9562 1.50 1396.00 27200 13300 13300 0.3053 0.50 1395.50 26000 0 0 0.0000 0.00 Vbmp = 71400 1.6391 Vbmp Water Depth = 2.5 Areas ,F,, and "G" Areas 'IF" and "G" are drainage areas in the post—developed condition that are primarily comprised of park site and commercial land use. The comparable drainage area in the pre—developed, or existing condition is Area 13. The low flows that require water quality treatment for this area originate from the park site and commercial site building pad. Since the site plans for these parcels are not available at this time, the impervious fraction cannot be calculated accurately. Accordingly, the applicable BMP devices will be designed and installed in accordance with NPDES guidelines at the time the site plans are proposed for these developments. These water quality treatment facilities are anticipated to be located within the park site and within the commercial development. The higher storm flows are designed to discharge into the existing 36" and 18" culverts located in Camino Del Norte. The rational analysis indicates that the combined developed condition peak flow rates of Areas 'IF" and "G" are less than the total pre—developed condition peak flow rate of Area 13. It follows, consequently, that the capacity of the existing culvert will not be exceeded and therefore no storm mitigation is required for this area. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. Area "H" Area "H" is a drainage area in the post—developed condition that is primarily comprised of natural area. The comparable drainage area in the pre—developed, or existing condition is Area 14. Since the vast majority of H: \265324\Final,\llydrology\Rcporl\:32a Report Body.dog x — 24 — Spyglass Ranch Tract 35337 Hydrology Study Table 15: Basin #3 Detention Basin Route Summary Duration QPK (cfs) UHD QPK (cfs) QPK (cfs) Max Water (hr) into basin UHD out of reduction Depth in basin Basin (ft) 6 31.0 16.3 14.7 4.6 24 9.5 8.4 1.1 1 3.4 Notes: 1. UHD = unit hydrograph for Area "D" 2. Q is 10—Year Strom Frequency. Area "D" contains minor sub—areas 11D.18" and "D.19," which are located along the east Spyglass Ranch boundary, that are comprised of natural area and manufactured slope area. These minor sub—areas are correlated to existing Areas 6, 7, and 8 for purposes of comparison. These areas are not tributary to Basin #3, as is the main portion of Area "D." These areas will drain to the east onto the adjacent downstream property, Tract 32013. The minor developed condition sub—areas produce a lower tributary drainage area when combined and compared to the correlating existing condition drainage areas under both the Stage 1 and Ultimate scenarios. The rational analysis indicates that the total developed condition peak flow rate of Sub—Areas "D.18" and ,D.19" is less than the total pre—developed condition peak flow rate of Areas 6, 7, and 8. It follows, consequently, that no storm mitigation is required for these sub—areas. Area "E"and Basin-4 Area "E" is a major drainage area in the post—developed condition that is comprised of one—quarter acre residential development, multi—family development, and commercial land use. The comparable drainage area in the pre—developed, or existing condition is Area 12. The first flush, or low storm flows for Area "E" will be designed to bifurcate into Basin #1 for water quality treatment. Because there is a favorable percolation rate at this site, Basin #1 is designed as an infiltration basin. The percolation rate based upon the percolation evaluation that was performed at the basin site is 5 minutes—per—inch.' The corresponding design infiltration rate based upon RCFCD guidelines is 2.37 inches—per—hour. The complete basin design worksheets are provided in the WQMP. The high storm flows are designed to discharge into the existing 54" culvert located in Camino Del Norte. The post—developed tributary area is significantly less than the pre—developed area to the same outlet point. The rational analysis indicates that the total developed condition peak flow rate of Area "E" is less than the total pre—developed condition peak flow rate of Area 12. By in large, this is due to the reduced drainage area in the post—developed condition that is being conveyed to the existing 54" culvert. It follows, consequently, that the capacity of the existing culvert will not be exceeded and therefore no storm mitigation is required for this t Ref: "Limited Percolation Evaluation," by GeoTek, Inc. prepared July 22, 2009. R:\265324\Final\llydro1ogy\Report\324 Report 13ody.doex — 23 — Spyglass Ranch Tract 35337 Hydrology Study Table 13: Basin #3 - Depth vs. Outflow 1.96 1586.66 0.121 0.00 0.00 0.12 61.45 1.63 1586.33 0.111 0.00 0.00 0.11 58.26 1.30 1586.00 0.099 0.00 0.00 0.10 54.88 0.96 1585.66 0.085 0.00 0.00 0.08 51.17 0.63 1585.33 0.069 0.00 0.00 0.07 47.28 0.30 1585.00 0.047 0.00 0.00 0.05 43.05 Notes: 1. (3) 1 in. dia. orifices in exterior baffle wall, invert elev=1584.66. 2. (3) 12 in. dia. orifices in exterior baffle wall, invert elev=1587.15. 3. 6 ft. wide baffle wall structure, top wall elev=1590.00. 4. Main outlet Q used to confirm WSE inside baffle chamber. Q not used in determining the route rating curve. Tables 14 summarizes the outlet structure design for Basin #3. Table 14: Basin #3 Outlet Structure Design Summary Outlet Structure Orifices (Stages 1 and 2) Invert Number Invert elev. of Dia. (in) Area Elev. above Remark orifices (sf) (MSL) bottom (ft) Stage 1 3 1.0 0.016 1584.70 2.76 At baffle wall Stage 2 3 12.0 2.356 1587.65 5.25 At baffle wall Main 1 36 7.069 1583.40 0 At headwall Outlet Baffle Wall Weir (Stage 3) Invert Weir elev. Crest L (FT) above Elev. bottom (MSL) (ft) 6.0 8.10 1590.00 Basin #3 is designed to maintain a minimum freeboard of 1.0' and maximum freeboard of 2.0' from the spillway crest elevation. Table 15 provides a summary of the basin detention performance. K: \265324\Final\llydro1ogy\12cport\324 Report 13ody.doex - 22 - Spyglass Ranch Tract 35337 Hydrology Study Table 12: Basin #3 - Volume Vs. Depth for Water Qualityl Contour Contour Volume Total Total Volume Basin Elevation Area (CF) Volume (Acre-FT) Depth (SF) (CF) (FT) 1587.33 15700 4670 24456 0.5614 2.63 1587.00 12600 4043 19787 0.4542 2.30 1586.66 11900 3828 15744 0.3614 1.96 1586.33 11300 3581 11916 0.2736 1.63 1586.00 10400 3102 8336 0.1914 1.30 1585.66 8400 2393 5234 0.1201 0.96 1585.33 6100 1716 2841 0.0652 0.63 1585.00 4300 1125 1125 0.0258 0.30 1584.70 3200 0 0 0.0000 0.00 Vbmp = 21600 0.4959 Vbmp Water Depth = 2.4 Notes: 1. Volumes shown use the upper and bottom stages of basin. Forebay volume is not included in the computations. Table 13 provides a summary of Basin #3 Depth vs. Outflow, as utilized in the routing analysis. Note that the basin has an outlet structure that is designed to provide storm and water quality mitigation. Table 13: Basin #3 - Depth vs. Outflow WS Stage 1 Stage 2 Stage 3 Cumulative Main Depth Elevation Q (cfs)l Q (cfs)2 Q (cfs)3 Outflow Q Outlet Q (cfs) (cfs)4 6.80 1591.50 0.226 24.49 37.15 61.86 96.87 6.30 1591.00 0.218 22.84 20.22 43.28 93.83 5.80 1590.50 0.209 21.07 7.15 28.43 90.69 5.30 1590.00 0.200 19.13 0.00 19.33 87.44 4.96 1589.66 0.193 17.69 0.00 17.89 85.16 4.63 1589.33 0.186 16.18 0.00 16.36 82.88 4.30 1589.00 0.180 14.50 0.00 14.68 80.54 3.96 1588.66 0.172 12.54 0.00 12.71 78.06 3.63 1588.33 0.165 10.29 0.00 10.46 75.57 3.30 1588.00 0.157 7.38 0.00 7.54 73.00 2.96 1587.66 0.149 1.25 0.00 1.40 70.25 2.63 1587.33 0.141 0.00 0.00 0.14 67.47 2.30 1587.00 0.131 0.00 0.00 0.13 64.58 R: \265324\Final\1lydrology\Report\324 Report Body.docx - 21 - Spyglass Ranch Tract 35337 Hydrology Study hI ^ LJ The higher storm runoff that enters the basin from this area is mitigated for the 10-Year storm in accordance with the Conditions of Approval. The entire runoff from this sub-area is designed to drain into the detention basin and onto to the adjacent downstream property to the south through the basin's outlet pipe. The basin is sized to retard the necessary flow such that the overall required historic flow rates tributary to that property are not exceeded (i.e. 6 and 24 hour storm durations for the 10-Year storm frequency). Basin #3 is also designed as a water quality facility that will treat the first flush flows from the entire tributary area as required by NPDES guidelines. Table 11 provides a summary of Basin #3 Volume vs. Depth relationship, as utilized in the basin routing analysis. Table 12 provides a similar summary of Basin #3 Volume vs. Depth relationship, except as related to the required water quality treatment. Table 11: Basin #3 Volume Vs. I?cth Contour Contour Volume Total Total Basin Elevation Area (SF) (CF) Volume Volume Depth (CF) (Acre-FT) (FT) 1591.50 28000 13600 114130 2.6201 6.80 1591.00 26400 12800 100530 2.3079 6.30 1590.50 24800 12025 87730 2.0140 5.80 1590.00 23300 7524 75705 1.7379 5.30 1589.66 22300 7194 68181 1.5652 4.96 1589.33 21300 6864 60987 1.4001 4.63 1589.00 20300 6551 54123 1.2425 4.30 1588.66 19400 6237 47573 1.0921 3.96 1588.33 18400 5924 41336 0.9489 3.63 1588.00 17500 5627 35412 0.8129 3.30 1587.66 16600 5330 29786 0.6838 2.96 1587.33 15700 4670 24456 0.5614 2.63 1587.00 12600 4043 19787 0.4542 2.30 1586.66 11900 3828 15744 0.3614 1.96 1586.33 11300 3581 11916 0.2736 1.63 1586.00 10400 3102 8336 0.1914 1.30 1585.66 8400 2393 5234 0.1201 0.96 1585.33 6100 1716 2841 0.0652 0.63 1585.00 4300 1125 1125 0.0258 0.30 1584.70 3200 0 0 0.0000 0.00 R: \265324\Final\llydrology\Report\324 Report Body.doex - 20 - Spyglass Ranch Tract 35337 Hydrology Study scenarios in order to determine the required interim and ultimate condition facilities. In short, the developed condition storm flows will be discharged to the matching existing drainage course under the Stage 1 condition and conveyed to the west to join the Wasson Canyon Creek. Under the Ultimate condition, the developed condition storm flows from this drainage area will connect to the South Shore storm drain system to be conveyed to the South Shore drainage basin. Area "D" and Basin #3 Area "D" is a significant drainage area in the post-developed condition that is comprised of one-quarter acre residential development in the south-easterly vicinity of the site. The primary comparable drainage area in the pre-developed, or existing condition is Area 9. This area is entirely tributary to Basin #3. Since, Area "D" is impacted differently under each of the Stage 1 and Ultimate scenarios, this study evaluates the drainage area under both scenarios in order to determine the more critical condition. In short, the Stage 1 developed condition will generate a higher tributary area than the Ultimate developed condition will generate at the drainage area's outlet point. Therefore, the Stage 1 scenario drainage area is used in modeling the unit hydrograph for Area D (UHD) that is used in the basin routing analysis. The unit hydrograph analysis for this sub-area is evaluated for two areas: (1) Unit Hydrograph "D" (UHD) for the Stage 1 Grading Design, and (2) UHD for the Stage 1 Grading Design Tributary to Basin #3. UHD under the first condition generates a higher tributary area to the adjacent downstream development primarily due to the offsite grading in that vicinity. Accordingly, the first hydrograph is used in comparison with the Existing Condition Unit Hydrograph 9 (UH9) in order to determine the total required mitigation. The second hydrograph is used in the basin routing analysis to determine the detention basin performance. Exhibits for each of the hydrographs are provided in the Exhibits section of this report. Table 10 provides a summary of the existing vs. proposed hydrograph results and the corresponding Q reduction required in order to match the historic flows. Table 10: Unit Hydrograph Summary - 10-Year Storm Frequency Duration QPK (cfs) UH9' QPK (cfs) UHD2 Required QPK (cfs) (hr) (Existing) (Proposed) reduction 6 32.8 35.0 2.2 24 10.7 10.7 NIL Notes: 1. UH9 = Unit hydrograph for Area 9. 2. UHD = Unit hydrograph for Area I'D" under Stage 1 Grading Design. R: \265324\Final\llydro1ogy\Rcporl\324 Report 13ody.doex - 19 - Spyglass Ranch Tract 35337 Hydrology Study prepared for the multi—family development. These water quality treatment devices are anticipated to be located within the multi—family development. Area "C" (JDA Area) Area "C" is a major drainage area in the post—developed condition that is comprised of about half of the east side of the site. The comparable drainage area in the pre—developed, or existing condition is Area 4. This area is tributary to the adjacent downstream property to the north, namely Tract 31593, South Shore (see Figure 6). TRACT 31593 I i i i TRACT 35337 i i Figure 6: Developed Areas Tributary to Tract 31593 No Scale The drainage course of Area 4 exits and enters the Spyglass Ranch north property line at multiple locations, making it difficult to meaningfully compare pre—developed and post—developed flow rates. Largely due to the convoluted nature of Area 4, this drainage area presents a special condition that is resolved by a drainage acceptance agreement on the part of South Shore and to the benefit of Spyglass Ranch as part of the overall joint development agreement (JDA) between the two projects. In other words, it is mutually agreed upon that there is no requirement for Spyglass Ranch to mitigate for any incremental increase in runoff due to development that may enter the South Shore property as a result of Spyglass Ranch developing its property. The JDA stipulates that South Shore will accept all of the tributary developed area from Spyglass Ranch. South Shore will convey and provide the necessary water quality treatment for these storm flows prior to the waters being discharged to Wasson Canyon Creek. Since, Area "C" is impacted differently under each of the Stage 1 and Ultimate scenarios, this study evaluates the drainage area under both H: \265324\Fina1,\11ydro1ogy\RcporL\324 Report Body.docx — 18 — Spyglass Ranch Tract 35337 Hydrology Study Per the PM 30985 grading and improvement plans, the approved design Q for the existing RCB culvert is 185 cfs in the Spyglass Ranch pre—developed condition. In the Spyglass Ranch post—developed condition, the total Q delivered to the existing RCB culvert is 181 cfs, which is within the approved design Q of 185 cfs. Table 9 summarizes the total resulting flows entering the existing RCB culvert in the proposed condition. Table 9: Post—developed Q Summary to Existing RCB Culvert Hydrology Q Runoff Source Description Map Node (cfs) Number PM 30985 Onsite Runoff n/a 40 Spyglass Area "A" (Basin #2 outlet)' 0.120 73 Spyglass Area KB" via PM 30985 0.202 43 Spyglass Minor Runoff 207;209 3 Street runoff (catch basins at PM 30985) n/a 18 Street runoff 144 4 Total Q to RCB Culvert: 181 Notes: 1. Q shown from Basin #2 outlet is post mitigation. Area KB" Area "B" is a significant drainage area in the post—developed condition that is comprised of a multi—family parcel and an offsite tributary area. The closest comparable drainage area in the pre—developed, or existing condition based upon the drainage outlet is Area 2. One may observe that Area 2 is much larger than Area "B". This is due to the proposed onsite grading that causes a large portion of the existing drainage area that is tributary to PM 30985 to be redirected to the Spyglass Ranch drainage basin and away from the existing Area 2 outlet point at the common boundary. The post—developed runoff from this area will drain onto PM 30985, as it does in the existing condition. PM 30985 is to provide a storm drain inlet structure to intercept this runoff. The peak flow rate in the developed condition that will discharge to PM 30985 at the common boundary is 43 cfs, which is significantly less than both the historic flow rate at that location, and the approved flow rate anticipated by PM 30985 of 128 cfs. Therefore, no mitigation is required at this location. Tables 2 and 3 provide a complete summary of the rational method analysis for each drainage area. The low flows that require water quality treatment for this area originate primarily from the multi—family building pad. Since the site plan is not available at this time, the impervious fraction cannot be calculated accurately. Accordingly, the applicable BMP devices will be designed and installed in accordance with NPDES guidelines at the time the site plan is H: \265324\Final\llydro1ogy\Report\324 Report Body.docx — 17 —