Infiltration Soil Water Flashcards
Terrasphere
water moves through the soil in response to both gravity and tension
Gravity
water flows to center of earth, downward
Tension
water is adhesive and holds onto soil; under stress; pulled in opposite directions
Soil Formation
takes hundreds of years to make 1 inch
Soil Formation Factors
parent material, time, climate, geology, biological agents
Parent Material
igneous, sedimentary, metamorphic
Climate
black, red, rocky, solid
“Black” Horizon
leaching zone organics here, most roots, susceptible to erosion
“Red” Horizon
accumulation zone, nutrients collect here
“Rocky” Horizon
weathered bedrock here
“Solid” Horizon
bedrock here
Moves Soil
water, wind, glaciers, finger lakes region
Residual Soil
soil material which is the result of weathering and decomposition of rocks that has not been transported from its original place
Colluvial Soil
loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combination of these processes
Marine
of, found in, or produced by the sea
Lacustrine
relating to or associated with lakes
Alluvial
moving water
Fluvioglacial
water from ice
Glacial
ice
Aeolian
wind
Soil Texture Classes
silt, clay, sand, loam
Characterizing Soil
texture class, particle size, porosity, hydrologic soil group
Particle Size Example
fine gravel > coarse sand > medium sand > fine sand > silt and clay
Why do we need particle size standards?
The amount of open space between the particles influences how easily water moves through a soil and how much water the soil will hold
Soils are Non-homogeneous
usually a mix of sands, silts, clays (texture classes)
Soil Texture Triangle Example
30% Clay, 10% Silt, 60% Sand
Bucket of Soil
dirt (solid), water (liquid), air (gas)
Total Volume
Volume Water + Volume Air + Volume Solids
Soil Water
water in soil; fills the voids and pushes out the gases
Hydroscopic Water
typically not removed
Depth
how we talk about volume of water
Porosity
volume of voids / total = n ; quality or degree of having minute spaces or holes through which liquid or air may pass
Density of most Soil Particles
160-170 lbs./ft^3 or 2.6-2.75 g/cm^3
Typical Porosity
30-60%
Infiltration
precipitation seeping into the ground; from atmosphere to the soil
Infiltration Units
length or length/time; total or rate
Measuring Infiltration
nearly impossible, would disturb the sample; can be inferred
What we want to know about infiltration
how much enters the soil
Percolation
downward movement of water through the soil profile
Percolating Water
can move as a saturated front under the influence of gravity OR can move as an unsaturated front due to capillary forces
Smaller Pores
fill first and empty last
Bigger Pores
fill last and empty first
Why Big Pores Empty First
water is too heavy to hold onto soil/rock/gravel
Engineering
interested in strenth of soil and amount of runoff (and timing of it)
Field Capacity
difference between saturation and wilting point; how much can soil hold before it runs (%)
Wilting Point
most water has left/is gone; plant can no longer suck more water up, and droop; farmers starting irrigation process (expensive)
Clayey
low permeability and high runoff
Loamy
moderate permeability
Sandy
rapid permeability and low runoff
What affects infiltration?
surface characteristics: vegetation, blacktop, forest, roofs
Bare Ground vs Crops: Bare Ground
increases runoff and flood risk; decreases infiltration
Bare Ground vs Crops: Crops
increases infiltration; decrease runoff and flood risk
Water Table
as it rains, it rises/increases; where water is at underground; wells drill to this and past it
Average per Capita
80 gal/person/day
How does the infiltration rate change during a storm?
decreases over time; depends on type of soil and surface
Measure infiltration rate of soil
worry more about the runoff
Infiltration Rate Methods
Horton, Green-Ampt, SCS Curve Number
Constant Percentage Method
doesn’t change over time, not truly realistic; assumes watershed is capable of infiltrating value proportional to rainfall intensity; 25% infiltration and 75% runoff
Constant Percentage Method Equation
1 - (direct runoff / total precip) * 100 = %
Exponential Decay - Horton
purely mathematical, will reach equilibrium; below arch is infiltration and above is runoff
Watershed Recovery
hard to predict
SCS Meaning
Soil Conservation Service
SCS Curve Number
empirical method of estimating excess precipitation; (F/S)=(Q/P)
SCS Curve Number Equation
Q = (P - 0.2S)^2 / (P + 0.8S)
calculates runoff
Q
amount of runoff leaving watershed; units: inches
P
precipitation; needs to be greater than Ia to start generating runoff; units: inches
S
max amount of water being held; units: inches
Ia (Initial abstraction)
accounts for all losses prior to runoff; 0.2S; units: inches
precipitation has to exceed this ____ of max storage before generating runoff
20%
Estimating S
(1,000 / CN) - 10
CN Meaning
curve number
CN
runoff for specific land uses; ranges from 1 to 100 (not really); grouped A to D
Solar Panels
no equation for figuring out infiltration and runoff for them
Saturation
porosity has been reached, max amount of water is being held
Water Year Starting Date
October 1st