MISSION BAY — Crews began preparations last week for sand to be dredged from the bottom of the Mission Bay Channel. Large pipes will carry sand from the channel to a one-mile stretch of south Mission Beach to fortify the shoreline. The pipes will reach as far north as San Juan Place. San Diego Mayor Jerry Sanders secured federal stimulus funds to pay for the $5.3 million project. The project aims to increase the safety of boaters by making the channel deeper, eliminating breaking waves that can cause danger to boaters. Lifeguard, commercial and recreational vessels traverse the channel. The dredging will begin Tuesday, Sept. 21and is expected to last about 30 days, said city officials.