Presentation: Groundwater Background Information
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Transcript of Presentation: Groundwater Background Information
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This work is supported by the National Science Foundation’s Transforming Undergraduate Education in STEM program within the Directorate for Education and Human Resources (DUE-1245025).
GEODESY AND WATER RESOURCES
Unit 2 Background
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OUTLINE
1. Terrestrial Water Storage (TWS) Defined2. Relationship between TWS and groundwater storage3. Depth to water table and groundwater storage4. GRACE Mission: 5. GPS vertical position
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ANNUAL HYDROLOGICAL CYCLE
Cockell, 2008 Fig. 1-38
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ANNUAL HYDROLOGICAL CYCLE: MAIN RESERVOIRS
Oceans
Atmosphere
Land38, 000
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Oceans
Atmosphere
Land38, 000
ANNUAL FLUX FOR THE OCEAN RESERVOIR
IN = 300+36=336
OUT
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ANNUAL FLUX FOR THE ATMOSPHERE
336+64=400
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RESIDENCE TIME FOR WATER IN THE ATMOSPHERE
Amount of water in the atmosphere (kg)Flux of water through atmosphere (kg/yr)tr =
tr =
tr =
336+64=400
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RESIDENCE TIME FOR WATER IN THE ATMOSPHERE
Amount of water in the atmosphere (kg)Flux of water through atmosphere (kg/yr)tr =
tr =13 x 1015 (kg)400 x 1015(kg/yr)
tr = 0.033 years = ~12 days
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ANNUAL HYDROLOGICAL CYCLE: MAIN RESERVOIRS
Oceans
Atmosphere
Land38, 000
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TERRESTRIAL WATER STORAGE (TWS)
1. TERRESTRIAL WATER STORAGE: ALL WATER STORED ON THE LAND SURFACE SURFACE WATER, SOIL MOISTURE, GROUNDWATER, SNOW, ICE, VEGETATION WATER CONTENT, AND PERMAFROST.
2. TWS: STORAGE TERM IN THE BASIN SCALE WATER BALANCE:
Two options for units: P, ET, and R as km3/yr or mm/yr;TWS as km3 or mm.
P = Precipitation ET = Evapotranspiration R = Loss to Rivers
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TERRESTRIAL WATER STORAGE (TWS) AND GROUNDWATER
IN MANY LOCATIONS, CHANGES IN GROUNDWATER STORAGE DOMINATE VARIATIONS IN TWS.
IN SOME LOCATIONS, SEASONAL VARIATIONS IN SNOW OR SOIL MOISTURE ARE ALSO IMPORTANT
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1350.62 m
Depth to water7 m
Well depth18 m
Measure groundwater levels
Water level = (surface elevation) – (depth to water)
Depth to water table measured at a well
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In > out replenished, water table/level goes upIn < out depleted, water table/level decline
porosity aread)replenishe(or volumedepletion increase)(or decline levelwater
RELATING CHANGES IN WATER TABLE TO CHANGES IN STORAGE
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Area
height area volumespace porePorosity
Groundwater volume change
Area
Groundwater level change in aquifer
= height
height area r volumegroundwatePorosity
height
porosity area r volumegroundwateheight
Why divided by porosity?
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GRACE MISSION: GRAVITY RECOVERY AND CLIMATE EXPERIMENT
“GRACE consists of two identical spacecraft that fly about 220 kilometers apart in a polar orbit 500 kilometers (310 miles) above Earth. GRACE maps Earth's gravity field by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. It is providing scientists from all over the world with an efficient and cost-effective way to map Earth's gravity field with unprecedented accuracy.
The gravity variations studied by GRACE include: changes due to surface and deep currents in the ocean; runoff and ground water storage on land masses; exchanges between ice sheets or glaciers and the ocean;……”
From: http://www.nasa.gov/mission_pages/Grace/overview/index.html#.VWcUAmRViko
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GRACE MISSION: GRAVITY RECOVERY AND CLIMATE EXPERIMENT
http://photojournal.jpl.nasa.gov/jpegMod/PIA04235_modest.jpg
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GRACE DATA CHARACTERISTICS:
2-6 month latencymonthly data (some months missing)coarse spatial resolution (~100’s km)
Castle et al., 2014, GRL
Colorado River Basin
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GPS VERTICAL POSITIONSolid earth responds elastically to changes in load, such as water loss during drought
instantaneous, reversible, linear
Drought: TWS decreases Wet period: TWS increases
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GPS NETWORKS
Thousands of stations across continental United StatesData latency of ~1 day
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HOW MUCH VERTICAL MOTION FROM TWS VARIATIONS?50 cm change in TWS ~20 mm up/downNoise in daily GPS position estimate ~2-3 mm
NLD
AS T
WS
(cm
)
P025: Idaho
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HOW MUCH VERTICAL MOTION FROM TWS VARIATIONS?
Response to loading depends on elastic parameter, Young’s modulus (E)
E = tensile stress / extensional strain
Units, are force/area (N/m2) or pressure (Pa).
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SPATIAL SCALE OF SENSINGDepends on horizontal scale of hydrologic load
0 250 500 500 250 Distance (km)
Disp
lace
men
t (m
m)
40 km wide2 m water equivalent
200 km wide0.5 m water equivalent
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2012 Drought: centered on High Plains
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Long-term TWS and GPS position variationsVariations in GPS position consistent across region
GPS
positi
on (m
m)
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Retrieve spatial pattern and magnitude of TWS variations
March 2014
Borsa et al., 2014
Borsa et al., 2014