Description: A 900 MHz survey in the outflow tunnel for a 200 year old embankment dam, for structural assessment and leak finding. We placed the SIR 4000 console at one end of the tunnel and used our long data cable (fortunately waterproof!) to connect to the antenna to minimise risk of dropping the console in the water. The outflow pumps for the dam were turned off before we went in and I was assured that they wouldn't come back on while we were down there!