Solution: In Rt△BCD, ∠ B = 90, ∠ BDC = 40, and DB=5m.

∫tan∠BDC =

BC/DB

Substitution data: BC = 5× tan 40 ≈ 4. 195.

∴EB=BC+CE=4. 195+2≈6.20m

EB is 6.20 meters high.

2

DE⊥BC, AF⊥BC and vertical foot are E and F respectively.

< ADC = 135, then < c = 45,

DE=DCsin45 =8*√2/2=4√2，

CE=DE=4√2

FE=AD=6，

BF=BC-CE-EF=30-6-4√2=24-4√2

AF=DE=4√2

tanB = AF/BF = 4√2/(24-4√2)=(3√2+ 1)/ 17≈0.30835，

〈B≈ 17. 13，

2、v=( 1/2)(6+30)*(4√2)* 100=7200√2≈ 10 180.8(m^3)

,

The construction of this dam requires earthwork 10 180.3 cubic meters.