Max distance Between storm water inlets

[Bison11]

A suburban street receives storm water runoff at rate of 2.0 L/m-s (on each side). The street has a slope of .8 percent and a cross slope of 2 percent; n = .013. If the street is 10 m wide and can be totally covered by water (depth = 0 at the midpoint), what is the max distance between inlets?

Thinking to use modified Manning's equation for triangular gutter cross section

Q = K(z/n)(s^.5)[y^(8/3)]

Q = gutter flow
z = reciprocal of the cross slope of the gutter
n = roughness coefficient
s= gutter slope
y = water depth at the curb
K = constant = .38 for metric


first I found the Q for the gutter flow
Q=?
z= 1/.02=50
n = .013
s= .008
y= 5m(.02)=.1m
K= .38

so Q = .38(50/.013)(.008^.5)[.1^(8/3)] = .28 m^3/s

at this point I am not sure how to use the runoff of 2 L/m-s and the Q = .28 m^3/s to get a max distance between inlets?

 

[Bison11]

may have figured this out. if I convert the L in 2 L/m-s to m^3 I get .002 m^2/s. then if I take (.28 m^3/s)/(.002m^2/s) = 140m. so basically this is a right triangle with a hypotenuse of 2L/m-s and leg1 = .28m^3/s and leg2 = length. Any thoughts or further info is welcome.