The next topic in hydraulics and

hydrologic systems concerns of hydrology principles.

In this segment,

we'll look at rainfall runoff relations by the curve number method,

the rational formula for predicting runoff, and the concept of hydrographs.

There are only a few topics discussed in the reference handbook, as shown here.

And the first one is the prediction of runoff from a catchment

from rainfall excess.

And the method that's given here is the National Resources Conservation Service,

which also, which used to be known as the Soil Conservation Service,

so-called curve number method, as given here.

This is empirical method which is based on observations of runoff

from fairly small catchments and hillside plots, slope plots.

And in this equation given here, Q is the total runoff in inches.

S is the storage capacity, also in inches,

which is the change in the stored aquifer water volume.

P is the gross rainfall in inches.

And CN is the so-called curve number,

which classifies the type of land use or the soil type involved.

If the watershed varies, for example, if we have some grassland,

some parkland some impervious areas such as parking lots, we have

to divide it into regions and analyze each one separately, or, alternatively,

compute an equivalent curve number by weighting the curve numbers by area.

And I'll give an example of that.

To illustrate this, here's a question.

The gross precipitation on a watershed is 8 inches and

the maximum storage is 0.5 inches.

The total runoff is mostly nearly which of these?