The URL can be used to link to this page

Home My WebLink About2022-05-19; Rancho Carlsbad Meeting (Districts - All); Harrison, DavidTo the members of the: CITY COUNCIL Date5/1q /:o£A ~CC ~ CM V ACM ✓DCM (3)....t::. May 19, 2022 ouncil Memorandum To: Honorable May · · d embers of the City Council From: David Harrison, As tor of Emergency Services Via: Scott Chadwick, Cit Re: Rancho Carlsbad ee mg (Districts -All) . {cityof Carlsbad Memo ID #2022063 This memorandum provides information on a meeting attended by city staff at Rancho Carlsbad on May 16, 2022. The city staff in attendance included David Harrison, Randy Metz, Darcy Davidson, Marie Jones-Kirk, Eric Sanders, Scott Lyle and Brandon Miles. The Rancho Carlsbad participants included Nancy Dungan, Creek Committee Chair, and others including HOA President, Park Property Manager and Creek Committee Members. This meeting was requested and hosted by the Creeks Committee Chair. The request included a question set for city staff. The agenda included the following topics: Flooding, erosion, sediment build-up and decrease in creek capacity, Preserve concerns, Calavera Dam and drainage systems. The Creeks Committee Chair started the meeting with a PowerPoint presentation detailing historical and contemporary issues and concerns, which transitioned into a question and answer discussion. The meeting lasted 90 minutes. Background Rancho Carlsbad has a long-standing relationship and dialogue with the City of Carlsbad related to creek and flooding concerns dating back to at lea.st 1998. In addition, current Rancho Carlsbad concerns include the possible impacts of future growth and climate change, and lingering concerns about past city actions and agreements related to flooding in Rancho Carlsbad. Discussion During the meeting, Rancho Carlsbad participants identified the following concerns: • Flooding and high water o In addition to generalized storm event flooding concerns related to Agua Hedionda Creek's path through Rancho Carlsbad (high water, bank erosion, debris flow, debris-caused creek flow blockage), the Rancho Carlsbad Creek Committee expressed a concern that in a high water event the abutment Carlsbad Fire Department 2560 Orion Way I Carlsbad, CA 92010 I 760-931-2141 t Council Memo -Rancho Carlsbad Meeting (Districts -All) May 19, 2022 Page 2 structures supporting the pedestrian bridge would impede water flow and create a debris dam. o Staff noted the newly constructed pedestrian bridge spans the 100-year flow limits and the support structures do not restrict these flows. Hydraulic analyses were performed documenting that the pedestrian bridge does not increase the 100-year flow elevations upstream of the bridge. o The Carlsbad Municipal Water District (CMWD) monitors water levels using Supervisory Control and Data Acquisition (SCADA) to set alarms for high water levels to control the flood control facility at Lake Calavera. • Erosion, sediment and debris build-up (upstream and downstream) o The city records Agua Hedionda Creek sediment levels annually between the El Camino Real and Cannon Road bridges. Sediment levels have not increased since initial readings were performed in 2013. • Dredging responsibility, cost and environmental limitations o Staff engaged in the discussion of environmental constraints and resource agencies stewardship roles. • Decrease in creek capacity and water flow rate o The Creek Committee presented concern that creek flood water removal capacity and water flow rates were decreasing. • Vegetation growth and clearing o The city does not have a Master Gardener on staff. Staff did not offer a solution as to how to eliminate cattails permanently. Staff suggested this issue would be best addressed by resource agencies. • Bare fields (water retention capacity) o The Creek Committee presented concern that agricultural fields with higher water retention capacity were being developed. • Water runoff from future development southeast of Rancho Carlsbad o City guidelines require that all new development mitigate potential increases to storm flow on-site. No increases in storm runoff are allowed from a new development site. • Calavera Preserve vegetation fire hazard and debris o Staff briefed the Creek Committee on weed abatement and vegetation management planning, noting environmental limitations in the preserve area. • Drainage basins efficacy o The detention basins that were constructed within the tributary watershed were analyzed and designed by professiorial engineers. Studies performed by these engineers show that these detention basins help reduce peak flows from larger storm events. Whether basins are regularly checked was a question to be referred to city maintenance and operations. Rancho Carlsbad participant voiced opinion that detention basins were not an effective strategy. Council Memo -Rancho Carlsbad Meeting (Districts -All) May 19, 2022 Page 3 • Calavera Dam inundation o Staff answered questions related to dam emergency plans, staff contacts, lowering dam levels prior to forecasted rains, drainage outlets, and rusted piping. Staff offered copies of annual State inspection reports and a tour of Calavera Dam. o The California Code of Regulations, Title 23, Division 2, Chapter 1, Article 6, Section 335, and subsections requires dam owners to have inundation maps prepared for dams regulated by the State. For Calavera Dam, the outlet pipe is a hydraulic control structure over 25 feet in height, so it is a critical appurtenant structure. • Drainage strategy and piping o The weir wall tunnel conveys flows from Basin BJB to Calavera Creek o Storm flows from the development to the north and along Cannon Road are captured and conveyed by a storm drain system that discharges to the drainageway running parallel to Cannon Road on the south side. o The 84" pipe extends from Basin BJB and westerly along Cannon Road towards El Camino Real. o A triple box culvert conveys flows under Cannon Road immediately east of El Camino Real. o The 84" pipe and triple box culvert both discharge to the open space located at the northeast corner of El Camino Real and Cannon Road. o As-built plans show that the 84" pipe is flowing at full capacity during a 100-year storm event. • What has been done by the city? o Weir wall and Calavera Creek rock slope protection at confluence point o Construction of an 84" storm drain paralleling Calavera Creek within Cannon Road o Repair and rehabilitation of the outlet works at the Lake Calavera Dam o Construction of three detention basins o 2006 emergency dredging o 2008 City of Carlsbad Drainage Plan o Carlsbad WMA Quality Improvement Plan -FY21 Annual Report Possible topics for elected officials at the next Rancho Carlsbad meeting: • Availability of federal or state grant, or other funding to improve drainage and flood control • Joint collaboration between the city, Rancho Carlsbad and resource agencies to address dredging • Effectiveness of detention basins as water mitigation strategy • City assistance with reducing flood risk at Rancho Carlsbad Council Memo -Rancho Carlsbad Meeting (Districts -All) May 19, 2022 Page 4 • Clear identification of surrounding property ownership and maintenance and compliance responsibilities • Upstream/downstream community boundary debris and flood control responsibilities cc: Celia Brewer, City Attorney Geoff Patnoe, Assistant City Manager Gary Barberio, Deputy City Manager, Community Services Paz Gomez, Deputy City Manager, Public Works Laura Rocha, Deputy City Manager, Administrative Services Michael Calderwood, Fire Chief Mickey Williams, Police Chief Kristina Ray, Communication & Engagement Director