River Crossing Security Currently the Rio Grande River is the border between Texas and Mexico, the 'Great Wall' would have to go straight down the middle of the river.  This is not practical and needs to be avoided.  The BorderTransportationSystem is designed to be built on the border, on Mexican soil, and on American soil as the terrain and need dictates.  Where the BorderTransportationSystem passes over a stream or river, or flood control basin, it must be made secure from below the water line to the underside of the bridge.  This can be done with a double wall of welded rebar or steel plate that will prevent human passage but allow for water flow.  The drawback is that debris may pile up on the upside of the barrier, and thus will have to be monitored and periodically cleaned. The screening will have to be monitored to prevent someone from trying to torch or cut his or her way through.  The screening should be anchored in a concrete base under the water and in the concrete of the bridge's under-bottom on the top.  The screening gaps should be wide enough for fish and aquatic animals to get through, but small enough to prevent the passage of a child or a bag of illegal product.  The two screen need to be separated by the width of the highway.  Index of ... Rail Infrastructure Solutions