Cubic Water

How much water do we have on Earth? Enough to form a cube that is 148 miles on each side!

How Wet is Wet?

We all know much of the Earth´s available water is in the oceans, and therefore, not really useable for much of what we need. Where´s the rest? Here´s the breakdown:

oceans 97% of all water
ice (glaciers, icecaps) 2%
groundwater 0.6%
surface water 0.01%

(It doesn´t add up to exactly 100% because of rounding, and because there is a tiny, tiny fraction in the atmosphere and soils.)

Waterfalls

Waterfalls are spectacular and awe-inspiring sights, but how do they form? Rock layers can differ in erodibility, being easier or harder for water to wear away. When harder materials overlie softer material, water eats away at the underlying rock, sometimes forming a waterfall.

Where Rivers Come From

What makes rivers happen? Many rivers start as streams in the hills and mountains of a region. Raindrops gather in rills and collect to form creeks, which flow downhill and join to form larger and larger streams. Finally, when streams are at least 100 miles long, they´re large enough to be classified as a river.

Deposition

Ever wondered why all that sediment builds up at the mouth of a river? When a stream enters a standing body of water, like a pond, lake, or ocean, the water is suddenly reduced in energy. That means some of the particles being carried in the water are now too large to transport, and are dropped by the stream.

Meandering Streams

Some streams run pretty straight, while others tend to meander - that is, they twist and wind their way along. Why is that?

Sometimes a stream needs all of its energy for down-cutting. Maybe it´s cutting through rock that´s hard to erode. Or maybe it´s quite high, and has a long way to cut down to get to the right elevation to join the next stream. Then it uses all of its energy to cut straight down.

On the other hand, if the rock isn´t very hard to erode, or if the stream is almost at the right elevation to join the next stream, it uses its energy for some downcutting but also for some side-cutting. That means the stream will develop twists and curves along the way, using its energy to erode back and forth and build a floodplain.

Stream Meanders

The natural course of a stream will typically be winding rather than straight. Since streams are dynamic, the twists and the bends move over time. If you build on the outside of a river bend (a "meander") expect your bank to be continuously cut away. If you build on the inside of the bend, however, you may find your property gradually increasing as sand and gravel are added to the bank.

Where Rivers Come From

What makes rivers happen? Many rivers start as streams in the hills and mountains of a region. Raindrops gather in rills and collect to form creeks, which flow downhill and join to form larger and larger streams. Finally, when streams are at least 100 miles long, they´re large enough to be classified as a river.

Streams and Groundwater

Many introductory geology texts include a chapter on water resources with diagrams of groundwater feeding a surface stream - and that happens a great deal, especially in the eastern US. But in the west, streams are often perched well above the water table, and rather than receiving groundwater, surface streams feed the underground water resources.

Perched Aquifers

A water-table (or "unconfined") aquifer is generally composed of two zones: an upper zone (the "unsaturated zone") that is dry or damp, and a lower saturated zone that yields water to a well. But sometimes the upper, unsaturated zone includes a layer that is impermeable - infiltrating water piles up on it and results in a perched water table that is closer to the surface than the main water table.

Sediment Transport

How does material as small as molecules or large as boulders get carried downstream? Some material, like salts, gets dissolved into the water. Other material is carried in suspension (making the water look muddy). The largest materials move downstream in a sort of skipping motion along the stream bottom, or are simply dragged along. Of course, some material is so large it is only moved during floodstage.

Porosity and Permeability

An aquifer needs to be porous and permeable - but what´s the difference? Porosity is the amount of void space in a rock or other earth material (like a sand deposit) - in other words, it´s how much water a material can hold.

Permeability refers to how well water flows through a material - that´s controlled by how large the pores are, and how well connected they are.

Infiltration

Streams can lose water to the ground (losing, or effluent streams), or can receive water from the ground (gaining or influent streams). The same stream can be losing some seasons and gaining others, or can be losing in one part of the stream and gaining in other parts.