obtaining flow data from stage hydrographs

[ml6ryan]

Hi,

I am very new to hydraulic modelling, so you may need some patience to follow my query..

I'm attempting to complete a paired catchment study to determine the extent to which a blue gum plantation affects water yield from a stream. This will be compared with a similar experiment set-up in a neighbouring sub-catchment, which is a perennial pasture.

I have data loggers set up in both streams which monitor the water level (stage). What I am having trouble with is converting the stages to a flow yield. I have two cross-sections surveyed at both sites; one at the data loggers, and one approximately 50 metres downstrem at both sites.

What i am basically asking is, how do I achieve a flow value for a particular stage height? I understand how to use Manning's N, and am familiar with how to change this. I'm just not sure how to enter the stage data, and achieve a flow value!

I would greatly appreciate someone's help with this.

Thanks,

M.

[Hydraulics Tool]

Q = (1.49/n)*A*R^0.67*S^0.5

Q = discharge (cfs or m^3/s)
n = Mannings n Value
A = Cross Sectional Flow Area (depth * width for a rectangular section), ft^2 or m^2
R = Hydraulic Radius = Area/Wetted Perimeter, ft or m
(Wetted Perimeter = 2*depth + width for a rectangular section)

S = energy slope (often bed slope is used, when uniform flow conditions can be assumed).

If working in SI units, use 1.0 instead of 1.49

1. Determine depth from stage (if not the same)
2. Compute Cross Section Flow Area, A
3. Determine Wetted Perimeter, P
4. Compute Hydraulic Radius, R
5. Determine energy slope, S
6. Determine n value (sounds like you know how to do this already)
7. Compute Q.