I agree with micalbrch . .You may assume a constant velocity flow since it seems that velocity requirement is not that crucial.
Say v = Q1/A1
where: Q1 (flow) = 10 m3/hr = 0.0027777 m3/sec
A1 (area) = pi (0.0508 m)^2 / 4 = 0.0020268 m^2
v = 1.37 m/sec
From this point...