General Plan - Moreno Valley

CHAPTER 6 – SAFETYFour types of actual and potential floodingconditions exist within the Moreno Valleystudy area: flooding in defined watercourses,ponding, sheet flow, and dam inundation.Flooding within defined watercourses occurswithin drainage channels and immediatelyadjacent floodplains. Ponding occurs whenwater flow is obstructed due to manmadeobstacles such as the embankments of StateRoute 60 and other roadways where theycross-defined watercourses. Sheet flowoccurs when capacities of definedwatercourses are exceeded and water flowsover broad areas.An extensive flood prone area exists alongthe Quincy Channel between CottonwoodAvenue and Cactus Avenue. An extensivefloodplain also extends along the OliverStreet alignment from a point north ofAlessandro Boulevard to John F. KennedyDrive and extending in a southwesterlydirection as far as the northeast corner ofMorrison Street and Filaree Avenue and thenortheast corner of Nason Street and IrisAvenue. Another extensive flood prone areaexists east of Heacock Street and Lateral Aof the Perris Valley Channel between CactusAvenue and a point north of the intersectionof Lateral A and Indian Street.Dam inundation is a potential, albeit remote,flood hazard through several portions of thestudy area. This condition is based on theassumption of instantaneous failure of a damwith the reservoir at or near its full capacity.Two locations of concern exist within thestudy area: Poorman Reservoir (PigeonPass Reservoir) and Lake Perris. Failure ofthe dam at Poorman Reservoir could resultin extensive flooding along the downstreamwatercourse. The risk of flooding due to damfailure is limited to the period during andimmediately after major storms. Thereservoir does not retain water throughoutthe year. Failure of the dam at Lake Perriswould only affect a very small area south ofNandina Avenue along the Perris ValleyStorm Drain and the Mystic Lake area in thesoutheast corner of the study area.MORENO VALLEY GENERAL PLANRCFCWCD prepared four "Master DrainagePlans" for the area. These documentsanalyze drainage flows and makerecommendations for improvements.The Moreno Area Drainage Plan is generallybounded by Nason Street on the west andTheodore Street on the east. The mountainrange to the north and the Mount Russellarea foothills to the south, define thenorthern and southern boundaries of thedrainage area. The plan includes tworetention basins north of State Route 60 anda network of open channels andunderground storm drains. The system willcarry storm runoff to a channel system and aretention basin in the Moreno Valley Rancharea that drains into the Perris Valley StormDrain.The Sunnymead Area Drainage Plan isgenerally bounded by Frederick Street andMarch Air Reserve Base on the west, thePerris Valley Storm Drain on the south andLasselle Street on the east. The planconsists of several retention basins, openchannels and a network of undergroundstorm drains. Poorman Reservoir is themajor flood basin in the area. The systemwill carry storm runoff south to the PerrisValley Storm Drain.The West End Area Drainage Plan is roughlybounded by the Box Springs Mountains tothe north, Old Highway 215 on the west,Alessandro Boulevard on the south, andFrederick Street on the east.The master plan calls for a system of openconcrete lined channels and undergroundstorm drains, which in conjunction withstreets, will allow for the safe passage ofstorm flows through the developed area.The system discharges storm runoff througha culvert on Old Highway 215 and intoSycamore Canyon.Page 6-24 July 11, 2006