HomeMy WebLinkAboutDexter Village TTM 38512 Tentative Review No. 1JASON E. UHLEYGeneral Manager-Chief Engineer1995 MARKET STREETRIVERSIDE, CA 9250I951.955.1200FAX 95 1.788.9965. www.rcflood.org262930RIVERSIDE COI-INTY FLOOD CONTROLAND WATER CONSERVATION DISTRICTIuly 29,2025Mr. Remon HabibCity EngineerCity of Lake Elsinore130 S. Main StreetLake Elsinore, CA 92530Dear Mr. Habib:ReDexter Village, TTM 38512Tentative Review No. IAccount No. 137-0-3 -90387As requested by the City of Lake Elsinore (City), the Riverside County Flood Control District and WaterConservation District (District) received the following for review on May 8,2025:Dexter Village Civil Plans; andDexter Village Drainage Report.The District's review is limited to the development of conditions of approval for the submitted plans as it relatesto the proposed District facilities. It is the District's understanding that water quality aspects of the plan anddrainage facilities to be maintained by the City or other public/private entities will be reviewed by the City.GENERAL CONDITIONS/T'LOOD HAZARD REPORT:Tentative Tract Map (TTM) 38512, referred to as "Dexter Village", proposes to construct new apartmentbuilding units, single family home units, drive aisles, parking lot areas, storm drain facilities and undergroundutilities. The 22.9-acre site is generally bound by undeveloped land to the north, Dexter Avenue to the south,3rd Street to the west and 2nd Street to the east. Existing access to the site is curently provided from DexterAvenue,3rd Street and2nd Street.The project would include the construction of an inlet structure and about 1,200 Linear Feet (LF) of 78"Reinforced Concrete Pipe (RCP) storm drain that would connect to the existing District's 78" RCP stub outwithin Third Street (Third Street Channel Stage 2,Drawing (DWG) No. 3-0210). This is consistent with the"Third Street Drainage Improvements - Technical Drainage Study" dated February 13,2018, and prepared byMichael Baker International for the City of Lake Elsinore which proposes the 78" RCP Dexter Avenue Lateralto convey the 10O-year flowrate of 382 cfs.The area is generally sloped to drain towards the southwest. In the existing condition, about 15.5 acres of thewestern onsite area drains to the southwest and across Dexter Avenue; there is a minor ridge across the site andthe remainingT .5 acre eastern onsite area drains southerly to a sump near the intersection of Dexter Avenue and2nd Street where flows pond and sheet flow across Dexter Avenue. The site is impacted by about 167.3 acres ofoffsite flows from the northeast. The offsite area consists of both ll4-acre residential lots and undeveloped areawith rolling hills to the east of the watershed. The offsite flow impacting the project site is estimated to have a100-year flowrate of approxim ately 320 cfs when applying a cfslac yield ratio to the Dexter Lateral I O0-yearflowrate determined in the aforementioned "Third Street Drainage Improvements - Technical Drainage Study".The project proposes to collect and convey onsite flows via curb and gutter and a storm drain network withinthe private streets. Storm drains range in size from 18" to 36" and are to be privately maintained by thehomeowner association (HOA). Onsite flows on the western portion of the site will be conveved to one of theI2
262930
Mr. Remon Habib -2- July 29, 2025
Re: Dexter Village, TTM 38512
Tentative Review No. 1
proposed HOA-maintained water quality bioretention/detention basins to mitigate onsite flows to meet the
downstream design 100-year Q of the proposed 78" RCP within Dexter Avenue. Flows from the eastern portion
of the site will drain to a HOA-maintained infiltration basin which is proposed to fully capture the storm volumes
of all storms aside from the 100-year 24-hour storm, which is proposed to have the excess flow bypass the
infiltration basin using a proposed spillway and surface flow to Dexter Avenue where an Arizona crossing is
proposed at the existing low point along with the project street improvements. These facilities include
connections to underground detention or infiltration basins; please note that direct connections from
underground detention facilities capable of routing down the 100-year flow to District facilities is prohibited.
The development of this site would increase 100-year peak flow rates from the existing condition that exceed
the design flowrate of the 78" proposed storm drain within Dexter Avenue. Onsite 100-year route down
mitigation shall be required to meet the Dexter Lateral design flowrate. A proposal for mitigation of the increase
of peak flow rates has been shown on the site plan and included with the land use application. Calculations
supporting the adequacy of the mitigation feature have been submitted to the Di strict for review. The flood
routing calculations for proposed Basin No. 1 and No. 2 are reliant on underground storage in order to mitigate
the developed flowrates to the existing condition; the 100-year mitigated volume storage must be fully provided
above ground and be capable of passing the 100-year peak flow without damage to the facility. The above ground
basin shall be designed per Appendix C – Basin Guidelines of Design Handbook for Low Impact Development
Best Management Practices, which can be found at https://rcwatershed.org/permittees/riverside-county-lid-bmp-
handbook/#93-96-appendices. (Correction No. 1).
The project proposes to protect the site from offsite flows by, including a depressed basin area along the project
boundary where the natural watercourse enters the existing site with two CB110 inlets at the invert sized to
collect the estimated 100-year flowrate of 320.3 cfs into the proposed 78" RCP. A perimeter wall is proposed
along the property boundary which would impede flows causing them to pond onto the adjacent parcel, APN
377-090-008; a 24" storm drain is proposed at the thalweg to convey the offsite flows under the perimeter wall
and to the proposed basin. The proposed inlet design is not acceptable, as the 24" RCP is not capable of passing
the 100-year peak flow into the basin area and the resultant ponding behind the wall could result in undermining
the wall's foundation and adversely affects the neighboring property. Additionally, the proposed CB110 inlet
design requires significant hydraulic head to meet the required inflow capacity. A more appropriate inlet design
would be to eliminate the perimeter wall where the natural watercourse enters the site and provide rock slope
protection or concrete apron and include a concrete cutoff wall at its edge where offsite flows cross the slope to
prevent undercutting and degradation of the slope. To capture the incoming offsite flow, a box culvert opening
with type "A" wingwalls per Caltrans Standard D84 may be required, which could then transition to the proposed
pipe. The proposed invert access ramp exceeds 10%, therefore, the access ramp shall be paved with grouted
Class I Rock (per Caltrans Section 72-3.02C). A concrete turnaround per District Standard Drawing M827 shall
also be provided at the inlet invert. District maintenance access needs are described in HDM Section 6.2.12.3
Inlet and Outlet Maintenance Access. (Correction No. 2).
The offsite flow is proposed to be conveyed through the site by a 78" RCP which proceeds southerly and is
aligned within private 'Street C' and an alleyway before proceeding westerly within Dexter Avenue public right
of way to connect with the existing District facility, Third Street Channel Stage 2. Onsite drainage facilities
located outside of the road right of way should be contained within drainage easements. The tentative tract map
shows a 30'-wide drainage easement over the 78" RCP where it is contained within 'Street C', however, where
the storm drain alignment proceeds down the alleyway, only a 24'-wide drainage easement is provided.
Depending on the proposed pipe cover, a 24'-wide drainage easement is likely not sufficient to provide for future
shoring for maintenance or repair of a 78" pipe. Refer to the 'Storm Drain Easement Widths' table which can be
found at https://rcflood.org/engineering-tools for required easement widths and provide the appropriate width as
it correlates to the proposed cover to be provided over the pipe. (Correction No. 3).
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Mr. Remon Habib -3- July 29, 2025
Re: Dexter Village, TTM 38512
Tentative Review No. 1
Additionally, the building setback for trenching shall adhere to the 2022 California Building Code (CBC) section
1809A.14 which states: "Unless otherwise recommended by the soils report, open or backfilled trenches parallel
with a footing shall not be below a plane having a downward slope of 1 unit vertical to 2 units horizontal (50
percent slope) from a line 9" above the bottom edge of footing and not closer than 18" from the face of such
footing." Otherwise, a structural and geotechnical report will be required to ensure the foundation of the
apartment buildings will be self-standing in the event the District needs to replace the storm drain in the future.
Please provide the plan and profile of the proposed 78" RCP on the project site to determine if the buildings are
appropriately setback (Correction No. 4).
Maintenance access will need to be provided through the site. A minimum width of 20' for the driving path and
an inside radius of 50' for turns shall be provided. It appears that a minimum width of 24' is provided throughout
Street "B", "C", "D" and "E" please confirm that this will not be obstructed by parked vehicles along the curb.
Additionally, it is preferred that a pullout area adjacent to the ramp inlet is provided so unloading of equipment
from the truck and trailer do not impact paved surfaces. The dimensions of a turnout area shall be at minimum
15 feet wide and 80 feet long outside of traveled ways per HDM Section 11.4.4 Stockpile/Staging Area (10
additional feet is needed when pulling off from residential traveled ways and is subject to change based on the
geometry of the roadway). (Correction No. 5).
The project proposes to mitigate generated onsite flows to an acceptable level to remain consistent with the
design flowrate determined by the "Third Street Drainage Improvements – Technical Drainage Study". Where
the 78" RCP enters public right of way, the design flowrate shall be 382 cfs as described in the "Third Street
Drainage Improvements – Technical Drainage Study" as additional area to the south is tabled to drain to this
lateral. The proposed alignment of the 78" RCP differs from the City adopted Lake Elsinore MDP but does not
stop the progression of the MDP and allows for the flow collection of the area south of Dexter Avenue planned
for this line. The proposed 78" RCP will be a future District maintained and operated facility and shall be
designed according to District standards.
The construction of the flood control facility(ies) that is(are) associated with this project may require a California
Environmental Quality Act (CEQA) document, particularly the inlet design and maintenance area for the inlet.
If needed, the CEQA document (i.e., Notice of Exemption, Initial Study/Mitigated Negative Declaration or
Environmental Impact Report) should include a description and environmental analysis of any new flood control
facility(ies) that will be constructed as part of the project or existing flood control facility(ies) that will be
impacted as a result of the project. Please note that if a draft CEQA document is submitted, the final adopted or
certified CEQA document will also need to be provided to the District prior to final District acceptance of the
flood control facility(ies).
The District has reviewed the submitted items listed above and has the following comments that shall be
addressed prior to the issuance of recommended conditions of approval:
1. The 100-year mitigated volume storage must be fully provided above ground and be capable of
passing the 100-year peak flow without damage to the facility. The above ground basin shall be
designed per Appendix C – Basin Guidelines of Design Handbook for Low Impact Development
Best Management Practices, which can be found at https://rcwatershed.org/permittees/riverside-
county-lid-bmp-handbook/#93-96-appendices.
2. The District will not maintain the basin inlet collection for offsite flows as currently proposed.
Revise the proposed inlet design to be consistent with District standards as detailed in the Hydraulic
Design Manual which can be found at https://rcflood.org/engineering-tools. For an acceptable inlet
design example, refer to Lakeland Village Line H Drawing No. 3-0207, Sheet Nos. 42-50.
https://content.rcflood.org/drawings/pdf/3-0207.pdfh.
3. Provide sufficient drainage easement width over the proposed 78" pipe along the entire alignment
in accordance with the 'Storm Drain Easement Widths' table which can be found at
https://rcflood.org/engineering-tools. The storm drain alignment or site layout may need to be
altered to accommodate this.
-4-262930July 29,2025Mr. Remon HabibRe: Dexter Village, TTM 38512Tentative Review No. 1Account No. I 37-0-3 -90387Provide the plan and profile of the proposed 78" RCP and determine if the buildings areappropriately setback in accordance with the2022 CBC; provide sufficient setback as necessary.Provide a minimum 20' drive aisle and inside radius of 50' for turns for adequate maintenance accessthroughout the site. Provide a 15'by 80'turnout areato unload equipment to maintain the inlet.Please confirm that the minimum 24' drive aisle provided for Street "B", rrcrr2 rrDrr and "E" will notbe obstructed by parked vehicles along the curb.Every effort has been made to identiff all potential areas of concern. However, the District may provide furthercorrections if additional public safety and health issues are discovered during review of subsequent submittals.Any questions pertaining to this project can be directed to Olivia Pearson at 951.955.1283 oropearson@rivco.org.Very truly yours,ALBERTChief ofServices DivisionecJames WaltersFairbrook CommunitiesEugene AbregoProactive Engineering ConsultantsOP:blj45