GEOS 617: Watershed Processes

Instructor: Jim McNamaraBoise State University

Outline

• 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• 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/watershed-hydrology/

Course Structure• 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.

• Course management will occur via the schedule: http://earth.boisestate.edu/jmcnamara/watershed-hydrology-schedule

• We will use publicly available data from several research watersheds throughout the US for most projects.

– Dry Creek: http://earth.boisestate.edu/drycreek/

– HJ Andrews: http://andrewsforest.oregonstate.edu/

– Reynolds Creek: http://www.nwrc.ars.usda.gov/

Schedule of Topics1. 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

• Each student will prepare a 7 minute MAX presentation consisting of 3-5 slides summarizing one “arrow”. Presentations must cover

– Basic governing physics– Essential equations used to describe/model the process– Measurement methods– Other relevant information

• Process Assignments– 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.

– What is diffusion?

– What is C?

– What is D?

x

CDQ

L

EKQ

Understanding motion requires understanding:-source and variability of the energy gradient-source and variability of the conductance term

• Darcy’s Law for Groundwater flow:

• Ohm’s Law for Electricity flow:

• Fourier’s Law for Heat flow:

• Dalton’s Law for Evapotranspiration

RVI

Water in Motion

L

TKQ

)( watKET

L

HKQ

Water in Motion

• Conservation of mass and energy

In

Out

Change in Storage

In – Out = Change in Storage

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

0

200

400

600

7/2 8/31 10/30 12/29 2/27 4/28 6/27

Dep

th (

mm

)

Total Precipitation

Water Input

Evapotranspiration

0

0.1

0.2

7/2 8/31 10/30 12/29 2/27 4/28 6/27

So

il M

ois

ture

0

10

20

30

Bed

rock F

low

(m

m)

15 cm30 cm65 cmBedrock Flow

0

20

40

60

7/2 8/31 10/30 12/29 2/27 4/28 6/27

Str

eam

flo

w

(lit

ers/

min

)

5

8

(m

g/L

)

Streamflow

dissolved solids

•Identify inflows•Identify outflows•Identify a steady-state time period

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– Precipitation formation– Snowmelt– Infiltration and redistribution– Overland flow– Saturated groundwater flow– Streamflow– Evapotranspiration

What is a Watershed

• 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)

– 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

• Scales can range from small ephemeral streams to the Nile basin– 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/

2011/08/wagon_wheel.pdf

Value Questioned!!• http://earth.boisestate.edu/jmcnamara/files/2011/08/Hewlett_defenseofwatersheds.pdf

History Explained• http://earth.boisestate.edu/jmcnamara/files/2011/08/Leopold_-Hydologic-

Research-on-Instrumented-Watersheds.pdf

Moving beyond the uniqueness of place

• http://earth.boisestate.edu/jmcnamara/files/2011/08/mcdonnell_movingbeyond.pdf

New Challenges• http://earth.boisestate.edu/jmcnamara/files/2011/08/Wagener-et-al.-future-

of-hydrology-evolving-in-a-changing-world-WRR-2010-2009WR008906.pdf

From experiment to observation• 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 long-term 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