is… Water soaking into the ground Why doesn’t rainwater always infiltrate into the ground?

What factors favors evaporation? It can evaporate…. What factors favors evaporation? 1.high temperatures 2.low relative humidity 3. Surface Area 4. Wind

It can run off….. What factors favor runoff? Runoff seems to have 1. slope 3. low permeability 2. lack of vegetation 4. saturated ground Runoff seems to have dominated here, why?

How do trees reduce flooding? trees intercept the rain evapotranspiration reduces the amount of water that reaches the river water is taken through the roots and so less enters the river

Here in the Badlands, runoff really dominated

Infiltration and groundwater

So what factors favor infiltration?

The first few inches of the ground, have a large effect on how much, and how fast water infiltrates. 1. Porosity – this is the volume of pore space compared to a given volume of particles 2. Permeability – this is the rate at which water flows into the ground 3. Capillarity – this is the total amount of water that clings to the surface of all the particles The type of particles here, and the way they are packed determine 3 important properties about infiltration

Porosity = volume of water needed to fill spaces (ml) x 100 volume of sediment (ml) Capillarity = volume of water retained (ml) x 100 volume of water needed to fill spaces (ml) Permeability = volume of water that drains through time (secs)

Here are 4 containers holding sorted particles. Note – sorted means all particles in the sample are of equal size Which container has the highest porosity? All the containers have the SAME porosity! For round particles, size does not affect porosity

Here are 4 containers holding sorted particles. Note – sorted means all particles in the sample are of equal size Which container has the greatest permeability? The bigger pore spaces allow water to travel through the soil faster.

Here are 4 containers holding sorted particles. Note – sorted means all particles in the sample are of equal size Which container has the greatest capillarity? D. The small pore spaces trap the water better

How does mixing different size particles together affect porosity? How does the shape of the particles affect the porosity? As each arrow flashes, indicate high or low porosity

A lab setup to test infiltration might look like this

How Particle Size Affects Infiltration 1). Porosity is NOT affected by particle size: Small particles make many small pore spaces Big particles make a few big pore spaces But the total amount of pore space is about the same in both cases!!!! (about 30%)

How Particle Size Affects Infiltration 2). Permeability IS affected by particle size: Water moving through small pores spaces moves slower due to friction, so…. Small particle sizes have lower permeability (clay) Big particle sizes have higher permeability (gravel)

How Particle Size Affects Infiltration Capillarity IS affected by particle size: Small pore spaces trap water better due to friction and surface tension, so Small particle sizes have higher capillarity (clay) Big particle sizes have lower capillarity (gravel)

How Particle Size Affects Infiltration 4) Unsorted sediments (many different particle sizes) affect infiltration: Small particles fill in the pore spaces between big particles, so Unsorted soils (like glacial till) have lower porosity and permeability, but higher capillarity, than sorted soils (like sand)

How Particle Shape Affects Infiltration 5) Shape of particles (rounded or angular) affects infiltration: Round particles make the biggest pore spaces, so Rounded sediments have higher porosity and permeability, but lower capillarity

Which has the highest.. 1. Porosity? 2. Permeability? 3. Capillarity?