Drainage Design Manual - the City of San Luis Obispo

• Exotic vegetation on the site should be removed in accordance with approvedrevegetation goals, plans and specifications.11.7 Project Planning and SchedulingTiming for a revegetation project is critical. Early planning to insure availability ofplant materials for fall planting is essential. Lead-time for plants that need to becontract grown can be one to two years (contract growing is often necessary becausemany native plants required for revegetation are not always commercially available).On certain project sites, effective pre-planning weed control can take an entire year ormore. Fall is a much better time for planting and establishing vegetation than thesummer. The best survival rates for plants planted on mid to lower creek banks areafter the chance of flooding is past. Timing of grass seeding is also critical. Properlytimed grass seeding is especially important where irrigation is not available, andwhere erosion control from grass growth is desired.11.7.1 Planting Site Preparation• Soil PreparationFor sites that have not been adversely affected by construction activities or preprojectimpacts, preparation of site soils is not generally necessary prior toplanting revegetation plants. However, the potential for a successful revegetationproject is greatly hindered on sites where soil compaction, poor drainage, loss oftopsoil, and/or excessive ruderal or exotic vegetation occur. In cases wheresignificant disturbances to existing soils are unavoidable, stockpiling of topsoils isoften a valuable practice. This is especially true on sites where subsoils areunfavorable for revegetation. Subsoils should be ripped and cross-ripped prior tospreading stockpiled topsoil.Pre-project assessments of the grass and herbaceous cover growing in areasproposed for revegetation should identify weed species and prescribe methods forcontrolling them both before topsoils are stockpiled, and again after they arespread. Compacted soils may be rectified by ripping, disking and/or rototilling.On steep gradients where erosion may be a problem, tillage operations should beperformed across-slope rather than up/down slope. Poor soil structure andpermeability can be improved by incorporating organic soil conditioners into thetop six to eight inches of the soil. Suitable amendments include chopped straw(free of seeds), mushroom compost, rice hulls, sawdust, ground fir bark, and/orother materials. Because of the high cost of these materials, soil conditioners arenot generally recommended for most revegetation projects. However, their use onseverely disturbed sites may significantly increase the initial survival percentageof revegetation plants. If revegetation goals include seeding, careful seedbedpreparation will increase germination and establishment potential.SLO Creek Drainage Design Manual 150 February 2003