解:过点C作CF⊥AD于点F,∵BC∥AD,BE是高,∴四边形BCFE是矩形,∴EF=BC=3米,CF=BE=6米,在Rt△ABE中,∠A=α=45°,∴AE=BE=6米,在Rt△CDF中,DF= CF tanβ = 6 tan63° ≈3.06(米),∴AD=AE+EF+DF=12.06(米),∴横断面(梯形ABCD)的面积为: 1 2 (BC+AD)?BE= 1 2 ×(3+12.06)×6=45.18(米2).