Question Deck 2 Flashcards
What are some of the different ways in which precipitation can be measured or estimated?
- Rain gauge- measures volume of water w/horizontal surface.
- Point measurements
- Satellites
- Radar
What are the primary sources of precipitation measurement error?
- Loss from evaporation
- Loss from wetting of gauge
- Over-measurement due to splash
- Under measurements due to turbulence
How can single-point precipitation measurements be scaled up to represent a watershed-wide estimation?
- Thiessen’s Polygons- boundaries within a catchment for various gauges
- Hypometric Methods- catchment elevation used to tell different rainfall between two elevations
What can cause variation in the water quality of precipitation?
- Elevation
2. Climate/Temperature
What is the difference between potential and actual evaporation, and under what circumstances would these values be the same or different?
- Potential evapotranspiration (PE)- the ability of the atmosphere to remove water from the surface through evaporation and transpiration assuming no control on water supply.
- Actual evapotranspiration (AE)- the quantity of water actually removed from a surface due evaporation and transpiration.
Why is measuring evaporation so difficult?
- Hard to do accurately with lots of variables
2. No perfect method
What is a key limitation for each of the various methods for measuring (direct and indirect) evaporation?
- Direct limits- require exspensive/sophisticated instruments, difficult to leave in the open over time, very small scale
- Indirect limits- Does not directly measure evaporation, accuracy errors
What are the four variables that must be directly measured when using the Penman model (or a derivative) to estimate evaporation? How does each variable influence the rate of evaporation at given place/time?
- Net Radiation- more leads to greater evaporation
- Wind Speed above canopy
- Relative Humidity- essential and determines saturation deficit
- Air Temperature- more is greater evaporation
What differentiates the phreatic and vadose zones?
Phreatic Zone- (groundwater) occurs beneath water table and is in the saturated zone. Below water table with little/no air
Vadose Zone- (soil water) above water table in the unsaturated zone. Above water table with interflow
What is meant by the terms permeability and porosity, and how does each affect the behavior of groundwater systems?
Porosity- ratio of voids/openings to the total volume of material, controlled by compaction
Permeability- how interconnected pores are with one another
What factors influence a soil’s infiltration rate?
- Infiltration capacity of the soil to receive water
- Capillary forces- surface tension/absorption
- Soil Suction/Moisture tension
What factors influence the rate at which water flows through an aquifer (i.e., which variables define Darcy’s Law)?
- Hydraulic conductivity (permeable/porous)
- Hydraulic Gradient
- Cross sectional of the aquifer
What type of geologic formations commonly serve as aquifers, and what conditions typically characterize their behavior as groundwater reservoirs?
- Soil above is saturated/decently permeable to yield water
- Has to have low permeability/porosity to prevent water from moving downward
- Igneous/Metamorphic works best
What are the three primary ways by which groundwater discharge occurs in natural hydrologic systems?
- Evapotranspiration
- Surface seeps/Springs
- Through-flow/seepage into streams
Lifting mechanisms that form precipitation
- Convective Lifting
- Orographic Lifting
- Frontal Lifting
- Convergent Lifting
