Murrieta Creek Master Drainage Plan Line-E (MDP Line-E)

This Project is divided into two distinct areas; the main channel area and the conservation area located at the northeastern corner of the channel (Figure 3). Area 1 – Main Channel The main channel area starts at Washington Avenue where a closed underground storm drain converts into an approximately 1,415 foot long unlined earthen channel. The earthen channel flows into a reinforced concrete box culvert underneath New Clay Street before discharging into Murrieta Creek. The box culvert is lined with a riprap armored apron for energy dissipation and erosion control. When the earthen channel was originally constructed, the design plans intended for the channel to be revegetated with native grassland species. A four foot swath of native grass was to be planted along the channel invert, while the remainder of the channel bed and banks were to be maintained free of vegetation to preserve hydrologic capacity. Current conditions differ substantially from the original design intent. The channel now supports emergent wetland vegetation buffered by a mature riparian forest and scrub community. Dominant riparian species include willow (Salix spp.), cottonwood (Populus fremontii), and mulefat (Baccharis salicifolia). Of particular concern, dense stands of cattails have become established in the channel invert and are expanding toward the banks. These stands are reducing conveyance capacity and causing water to pond during the dry season, leading to stagnant conditions. Routine maintenance is required to manage the spread of cattails and maintain intended channel function. Cattail population control will primarily involve selective application of aquatic approved herbicides. In addition, periodic vegetation management may also be needed to limit overgrowth of mature willows and cottonwoods along the banks to ensure adequate flood conveyance and reduce fuel loads. Area 2 – Conservation Area The conservation area consists of 400 feet long by 119 feet wide unmaintained earthen channel that was revegetated with native riparian species. This portion of the channel was designed to be a low-flow meandering drainage course adjacent to the main channel. Although the conservation area does not have an official conservation easement, vegetation within this area will be protected in place and no vegetation removal, trimming, or thinning is proposed. The only maintenance activity planned for this area is the selective application of herbicides to manage and control the expansion of cattail populations and non-native/invasive species.