Stormwater Treatment 1604 San Leandro Boulevard 042122

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C.3 STORMWATER TECHNICAL GUIDANCE cases, storn-water applications require a permanent irrigation system which shall be designed to maximize w ater conservation. Irrigation specifications and design plans shall be provided. Plants such as shrubs and trees grown in naturalized areas that are not saturated to the surface or inundated shall be irrigated with drip irrigation. The irrigation system shag remain in place for a minimum of three years, and should continue until it is demonstrated that the plantings can survive on annual rainfall and/or groundwater. Seeded areas do not need irrigation in years of normal rainfall. If a period of drought occurs after seeding, supplemental watering may be needed for gemination in the first year. The plants on the bottom and edge of the constructed basins should be flowed to become established for one growing season prior to the onset of significant flooding that will inundate the plantings for extended periods. The types of plants recomrnended for these locations are rushes, sedges, grasses and herbaceous species. Initially, saturated soils are required for the bioretention areas and extended detention basins during the establishment period of the plantings. After the plants have become established, inundation with a surface depth of 1 cm to 2 cm alternating with short dry periods is recommended for the basins during the first year. Iariodic shallow flooding of these basins can slow the growth of non-native weedy terrestrial species in the wetland system however, the water depth should not be greater than the height of the plants. This initial irrigation regime will prevent plant mortality from dry periods or excessive flooding in the first year, and reduce the growth of non-native weedy species. 6rergent species should be planted in saturated soil so the plants will become established. For emergent species, the water level in the first year should be maintained to allow for soil saturation or shallow inundation around the base of the plants. Significant flooding and inundation of stems and leaves of the plants should be avoided the first year. Tall plugs and plantings can tolerate greater depths of inundation if a significant portion of the stems and leaves of the plantings remain above the water surface. B.5 Monitoring and Maintenance General Requirements AD planted areas shall be monitored and maintained as required to ensure proper establishment by a Contractor with a valid Caltfomia G27 contractor's license. Frequency of site visits and required maintenance practices will vary depending upon the stormw ater measure and plant selection. Nfaintenance shall include watering, cultivation, weeding and pruning as necessary to maintain optimum growth conditions and, as appropriate to the speck storrwater measure, to keep the planted areas neat and attractive in appearance. In all instances, controlling w eeds and unw anted grow th w ith chemical applications is prohibited. The contractor shall be familiar with the design and function of the specific stormwater measure(s) to ensure that the plantings are maintained appropriately and do not interfere with the efficient runoff drainage and filtration. Ongoing management of invasive weed species is required in all applications. Nbrrthly hand weeding will allow the naturalized vegetation to take hold, and will ultimately be less costly than less frequent, and more intensive clearing. fegular application of compost mulch, or other APPENDIX B B-13