1. The Basics of Hillslope Hydrology with Examples from Tracer Studies in the Boulder Creek Critical Zone Observatory
Eve-Lyn Hinckley
Intro to Hydrology
3 Dec 2010

2. Historical Developments in Hillslope Hydrology Or:
How We’ve Explained in Various Ways that Water Runs Downhill
Freeze, 1974

3. Hydrologic pathways through the landscape
Hydrologic flow paths are the connection between land and water systems, affecting the distribution of reactive elements, and modifying the physical, chemical, and biological factors that control the fates and forms of reactive elements. Much work has been done to characterize the different hydrological flow paths within the terrestrial system, including…
Inspired by Dunne, 1980

4. Hydrological flow paths affect stream discharge patterns.
Cowie, 2010
Hydrological flow paths affect stream discharge patterns.

5. Infiltration excess (“Horton”) overland flow
Robert E. Horton
circa 1945
Photo: K. Caylon

6. Saturation overland (“Dunne”) flow
Courtesy: The Comet Program
Infiltration
Rainfall
Rate
Overland flow
Time
Tom Dunne in a Happy Valley trench
circa 1970s

7. Where and when do we observe these different mechanisms of overland flow?

8. Event-based study of wetting and drying within catchments.
Research by Wilson and Dietrich in Northern California.

9. (physics-based, distributed response)
How many holes can you stick in the ground?
We need models, and there are many different approaches…
TOPMODEL
(topography-driven)
InHM
(physics-based, distributed response)
After Loague, 2006

10. Hot off the press
Stable isotope studies show that trees access and transpire different water than appears in streams!
The ecohydrologists highlight the role of “the green stuff” (a.k.a. trees).

11. Add humans: climate and land use change + manipulation of water resources around the world change hillslope hydrology

12. How are we changing hillslope processes?
Climate change: altering precipitation amounts/timing and
temperature patterns
Agriculture: diverting and storing water, irrigating during dry seasons,
compacting soil surface
Urbanization: paving soil surfaces
(To name a few…)
Leads to: increased evaporation and runoff, decreased storage – an accelerated hydrologic cycle

13. Eve’s research interest: Hydrologic pathways through the landscape influence biological and chemical processes
Hydrologic flow paths are the connection between land and water systems, affecting the distribution of reactive elements, and modifying the physical, chemical, and biological factors that control the fates and forms of reactive elements. Much work has been done to characterize the different hydrological flow paths within the terrestrial system, including…
Inspired by Dunne, 1980

14. Mississippi River
Decisions about nutrient inputs at the local scale have consequences at the regional scale
N, P
The impact on elemental cycles occurs and is most easily seen at local and regional scales. N and P inputs to ag fields affect the Gulf of Mexico by causing increased primary productivity and eutrophication. However, one of the greatest uncertainties at this scale is in understanding how these elements travel across the landscape; how do they react as they move from the land to the water system? What is the pathway they take?
Gulf of Mexico Dead Zone
Source:

15. Hillslope tracer experiments in the Boulder Creek Critical Zone Observatory

16. CLIMATE AND ECOLOGICAL ZONES

17. 59% 70% 85% 85% Alpine Sub-alpine High Montane Montane
Figure 3: Amount and type of precipitation collected as part of the National Atmospheric deposition program (NADP) at for locations within Boulder Creek Watershed
59%
70%
85%
85%
Rory Cowie, in prep

18. Problem: Increases in Nitrogen Deposition at High Elevation from Human Activities
Eastern slope > 2x western slope, 75% from human activities (Baron et al. 2000)
NH4NO3

19. The “Reactor on a Slope”
Overarching research question of Boulder Creek CZO
Erosion = lowering, due to divergence of sediment flux (difference b/w inputs and outputs)

20. Research Questions
How do changes in dominant flow paths along a montane hillslope profile affect the fate and transport of deposited N?
(2) Do hydro-biogeochemical interactions differ on N- and S-facing slopes?

22. Ecosystem pools and fluxes measured

23. Ecosystem pools and fluxes measured

24. Snowmelt Tracer Study, 10 April 2010
SLOW application rate
40 days of daily sampling, 14 days of event-based sampling
LiBr + K15NO3- - N in water
SNOW

25. Some flow hypotheses for the South-facing slope? ?

26. Some flow hypotheses for the South-facing slope
Potential for hydrologic connectivity at depth, movement laterally, and reaching stream in spring
Low potential for hydrologic connectivity, unless there is a huge storm event

27. Some flow hypotheses for the North-facing slope
Snow accumulates, one big spring melt event
Freeze and thaw occurs in snowpack and soil throughout winter ? ?

28. Some flow hypotheses for the North-facing slope
Snow accumulates, one big spring melt event
Freeze and thaw occurs in snowpack and soil throughout winter
Potential for hydrologic connectivity at depth, movement laterally, reaching stream.
Potential for hydrologic connectivity and more preferential flow

29. How we start to infer hillslope transport processes from tracer data

30. Looking through the soil profile, by the creek

31. One of the challenges of hillslope hydrology in snow-dominated catchments: Modeling snowpack dynamics and melt water flux
Williams et al., 2010

32. A first attempt at modeling melt water flux
TRACER EXPT
Upper S-facing slope
Upper N-facing slope
Melt water flux (m3 m-2 day-1)
Work in progress with Bob Anderson

33. S-facing slope N-facing slope
Current challenge in hillslope hydrology: understanding flow paths and stream response at elevations where snowpack is variable in time and space and predicting how these areas will respond to long-term climate change. Water runs downhill, but there is still a lot to be done!
S-facing slope
N-facing slope