Transcript Slide 1

GEOS 617: Watershed Processes
Instructor: Jim McNamara
Boise State University
Outline
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Review course objectives
Review process overview assignment
Watershed definition
Water balance
Introduce water balance assignment
Intro Hydrology Course
(GEOS 416/516 Hydrology)
• Equations for each arrow
Watershed Hydrology
• Fluxes (arrows) and stores are not independent
• Hydrologic behavior emerges in response to the
integration of arrows that can not be predicted
by simply connecting the arrows
Watershed Processes
• Watersheds are fundamental landscape units that arise
from the interaction of climate, water, rock, and
vegetation
• Water flux pathways are dictated by landscape
properties in the short-term, which are dictated by water
pathways in the long-term
Watershed Processes
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Governing Principle for Course:
– Watersheds are fundamental landscape units that transport mass and
energy through terrestrial systems, and provide sustenance for
ecosystems and human societies. Holistic understanding, and effective
management, of watershed processes is predicated on recognizing the
interdependencies and feedbacks governing landscape evolution,
hydrology, and ecology
Course Logistics
• See web page:
http://earth.boisestate.edu/jmcnamara/wat
ershed-hydrology/
Course Structure
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This course requires active participation by all students. The instructor will
use lectures to introduce each new topic. Subsequent class periods will be
composed of student-led discussions and project work. To get the full
experience students must attend all class periods, complete all reading
assignments, and stay caught up on class projects.
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Course management will occur via the schedule:
http://earth.boisestate.edu/jmcnamara/watershed-hydrology-schedule
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We will use publicly available data from several research watersheds
throughout the US for most projects.
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Dry Creek: http://earth.boisestate.edu/drycreek/
HJ Andrews: http://andrewsforest.oregonstate.edu/
Reynolds Creek: http://www.nwrc.ars.usda.gov/
Schedule of Topics
1. Course introduction
-Summary of goals, objectives, and expectations
2. Hydrologic process review
-A brief review of the physics governing individual hydrologic processes operating in watersheds including precipitation, snowmelt, infiltration,
lateral surface and subsurface flow, groundwater flow, and streamflow.
3. Water Balance
-An advanced treatment of mass balance concept operating a hillslope, watershed, basin, and continentental scales
4. Watershed Geomorphology
-Quantitative analysis of the shape of watersheds, hillslopes, and channel networks; geomorphologic evolution of watersheds
5. Advanced concepts in watershed hydrology
-Integrated hydrologic processes and emergent hydrologic properties in watersheds.
-water residence time
-Runoff generation
-Storage, thresholds, and connectivity
6. Ecohydrology
-Relationships between hydrology, vegetation, and geomorphology in catchments
7. Watershed biogeochemistry
-An introduction to the role that hydrologic processes play in governing the export of mass from watersheds
8. Hydrologic modeling concepts
-A capstone topic reconciling our knowledge of watershed hydrology with current hydrologic modeling approaches
9. Watershed Management/ Idaho watershed issues
Assignment 1:
Process Review
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Each student will prepare a 7 minute MAX presentation consisting of 3-5 slides
summarizing one “arrow”. Presentations must cover
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Basic governing physics
Essential equations used to describe/model the process
Measurement methods
Other relevant information
• Process Assignments
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Precipitation formation
Snowmelt
Infiltration and redistribution
Overland flow
Saturated groundwater flow
Streamflow
Evapotranspiration
Water in Motion
• Key points
– Water moves in response to energy gradients
– Rate of movement depends on the magnitude
of the gradient AND material properties
– Moving water performs work (Newton’s Laws)
– While water is moving around, or changing
phases, conservation of mass and energy
must be obeyed
Water in Motion
• Consider Fick’s Law as a motion equation
– A diffusing substance moves from where its concentration is
larger to where its concentration is smaller at a rate that is
proportional to the spatial gradient of the concentration.
C
Q  D
x
– What is diffusion?
– What is C?
– What is D?
E
Q  K
L
Understanding motion requires understanding:
-source and variability of the energy gradient
-source and variability of the conductance term
Water in Motion
• Darcy’s Law for
Groundwater flow:
Q  K
H
L
• Ohm’s Law for Electricity
flow:
I  RV
• Fourier’s Law for Heat
flow:
Q  K
• Dalton’s Law for
Evapotranspiration
T
L
ET  K ( at   w )
Water in Motion
• Conservation of mass and energy
In
In – Out = Change in Storage
Change in
Storage
Out
Water in Motion
• Conservation of Mass
– Can be expressed in absolute quantities
• In – Out = S or I – Q = S
• If we instantly add 5 gallons of water into a bucket
and remove 3 gallons at the same instant, the
volume in the bucket has changed by 2 gallons
Water in Motion
• Conservation of Mass
– Can be expressed as absolute rates
• I/t –O/t = S/t
• If we add 5 gallons in one hour to a bucket and
remove 3 gallons in one hour, the volume in the
bucket has changed by 2 gallons in one hour
Water in Motion
• Conservation of Mass
– Can be expressed as instantaneous rates
• i-q = dS/dt
• If water is constantly added to a bucket at a rate of
0.25 gallons/hour and is constantly removed at 0.5
gallons per hour, the rate of change is -0.25
gallons per hour.
Water in Motion
• Conservation of mass in hydrology
– WATER BALANCE!
• Fundamental concept at all spatial and temporal
scales
Water in Motion
• Conservation of mass true for
– Conservative substances
– Defined control volume
– Defined time period
The Water Balance
• Consider the water (conservative substance) balance
of watershed (control volume) over a year
(specified duration).
– P +Gin – (Q+ET+Gout) = S
• Where is soil moisture, infiltration, interflow?
• What are the storage mechanisms?
More later
•Identify inflows
•Identify outflows
•Identify a steady-state time period
Total Precipitation
Water Input
400
Evapotranspiration
200
0.2 7/2
15 cm
8/31 10/30
30 cm
65 cm
Bedrock Flow
12/29 2/27
4/28
6/27 30
20
0.1
10
0
60 7/2
0
Streamflow
8/31
10/30 12/29 2/27
4/28
6/27
8
dissolved solids
40
20
0
5
7/2
8/31
10/30 12/29
2/27
4/28
6/27
(mg/L)
Streamflow
(liters/min)
Soil Moisture
0
Bedrock Flow (mm)
Depth (mm)
600
Assignment 1:
Process Review
•
Each student will prepare a 7 minute presentation consisting of 3-5 slides
summarizing one “arrow”. Presentations must cover
–
–
–
–
Basic governing physics (energy gradient, conductance…)
Essential equations used to describe/model the process
Measurement methods
Other relevant information
• Process Assignments
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Precipitation formation
Snowmelt
Infiltration and redistribution
Overland flow
Saturated groundwater flow
Streamflow
Evapotranspiration
What is a Watershed
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A watershed is the area of land where all of the water that is under it or
drains off of it goes into the same place. (http://water.epa.gov/type/watersheds/whatis.cfm)
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John Wesley Powell, scientist geographer, put it best when he said that a watershed is
"that area of land, a bounded hydrologic system, within which all living
things are inextricably linked by their common water course and where, as
humans settled, simple logic demanded that they become part of a
community."
What is a Watershed
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Scales can range from small ephemeral streams to the Nile basin
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We will focus on upland headwater systems in relatively natural states
THIS and smaller
NOT THIS
Experimental Watersheds
• Our knowledge of watershed hydrology
originates in part from a rich history of
“experimental watersheds”
– Experimental vs Observation
Experimental Watersheds
• Our knowledge of watershed hydrology
originates in part from a rich history of
“experimental watersheds”
– Experimental vs Observation
Wagon Wheel Gap
• 1921 Forest removal experiment
– http://earth.boisestate.edu/jmcnamara/files/20
11/08/wagon_wheel.pdf
Value Questioned!!
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http://earth.boisestate.edu/jmcnamara/files/2011/08/Hewlett_defenseofwatersheds.pdf
History Explained
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http://earth.boisestate.edu/jmcnamara/files/2011/08/Leopold_-HydologicResearch-on-Instrumented-Watersheds.pdf
Moving beyond the uniqueness
of place
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http://earth.boisestate.edu/jmcnamara/files/2011/08/mcdonnell_movingbeyo
nd.pdf
New Challenges
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http://earth.boisestate.edu/jmcnamara/files/2011/08/Wagener-et-al.-futureof-hydrology-evolving-in-a-changing-world-WRR-2010-2009WR008906.pdf
From experiment to observation
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http://www.cuahsi.org/docs/dois/CUAHSI-TR4.pdf
http://www.cuahsi.org/docs/dois/CUAHSI-SciencePlan-Nov2007.pdf
http://www.cuahsi.org/docs/stratplan/CUAHSI-5yr-StrategicPlan.pdf
http://www.cuahsi.org/docs/CUAHSI-SciPlan_Wilson.pdf
Advances in theory and
application require longterm observation
Our Observational Watersheds
• Dry Creek:
http://earth.boisestate.edu/drycreek/
• Reynolds Creek:
• HJ Andrews:
– http://andrewsforest.oregonstate.edu/
Water Balance Exercise
• http://earth.boisestate.edu/jmcnamara/files
/2011/08/catchmentWaterBalance.doc