# Hydrology

Hydrology is a science concerned with the properties of the Earth's water, especially its movement in relation to land.

The science of hydrology is also being applied to astronomical objects that contain water in various forms. For students interested in off-world water, several lectures have been included.

More appropriately, hydrology directly applied to the Earth may be called geohydrology.

## Content summary

Hydrology is the study of the water cycle. Natural and man-made processes guide water in its varied forms to a variety of ends. Use as irrigation, drinking water and process water by man is very common.

Def. "hydrology as used in the processing of radioactive materials" is called radiohydrology.

Def. the "study of the ecological processes associated with hydrology" is called ecohydrology.

Def. "the science that uses dendrochronology to investigate and reconstruct hydrologic processes, such as river flow and past lake levels" is called dendrohydrology.

## Theoretical hydrology

Def. the "science of the properties, distribution, and effects of water on a planet's surface, in the soil and underlying rocks, and in the atmosphere" is called hydrology.

## Learning Materials

### Hydrology Lessons

#### Diffusion

For a source contaminant concentration $\ C_{0}$  entering a flow of velocity ${\vec {U}}$  at a distance $\ x$  upstream from a point, the downstream concentration $\ C$  at that point is determined by the ratio...

${\frac {C}{C_{0}}}=e^{\frac {x*{\vec {U}}}{D}}$

Where... $\ D$  is the local dispersion coefficient determined by $\ D=0.067*depth*V_{f}$

and where friction velocity is $V_{f}={\sqrt {g*depth*ChannelSlope}}$

#### Velocity Distribution in an Open Channel (River)

Velocity distribution within a river follows a standard velocity profile for a confined space (pipe-flow)with the exception that the vertical distribution is truncated at the surface due to reduced friction with atmospheric gases versus the high friction against riverbed materials.

Boundary Layer thickness, also known as the displacement thickness, is defined by:

$\delta _{d}=\int _{0}^{H}{\frac {1}{H}}\left(1-{\frac {\vec {u}}{\vec {U}}}\right)dz$

where ${\vec {U}}$  is the average velocity and ${\vec {u}}(x)$  is the velocity distribution in a channel of uniform depth $\ H$ .

${\bar {U}}={\frac {\int _{A}\left(\rho {\vec {V}}\cdot {\hat {n}}\right)dA}{\rho A}}$

So in the case of this river, where the current is always normal to the cross-sectional area of the river (idealized)...

${\bar {U}}={\frac {\int _{x}\int _{y}\left(\rho {\vec {V}}\right)dydx}{\rho A}}$