Download Water Balance in Small Piedmont Watersheds

April James
Canada Research Chair – Watershed Analysis and Modeling
Department of Geography
Nipissing University
Contributions from: C. Dreps, K. Kuntukova, North Carolina State University
G. Sunn, J. Boggs. US Forest Service
Headwaters Workshop, February 25, 2011
Headwaters Workshop, February 25, 2011
Hydrologic response of headwater systems
 How water is generated
from the terrestrial system
and contributes to aquatic
environments.
 At small catchment scales,
terrestrial processes
dominate.
Headwaters Workshop, February 25, 2011
Experimental studies at the hillslope and small
catchment scales
• Hillslopes and small catchments
as a building blocks of headwater
systems.
• How can we compare rainfallrunoff response from different
experimental sites and
physiographic regions ?
• Are there similar behavioral
characteristics?
Generated from these studies….
 Process-level understanding that is critical for:
 Rainfall-runoff models
 Coupled hydro-ecosystem models
 Geomorphology models
 Land management decisions
(Recently summarized by Detty and McGuire, 2010)
Headwaters Workshop, February 25, 2011
Threshold rainfall-runoff response of hillslopes
and small catchments
 Recent focus on nonlinear or threshold rainfall-runoff
response – as a common, generalizable behaviour?
 A function of:



Storm size (Tromp-van Meerveld and McDonnell, 2005;
Uchida et al., 2005)
Antecedent soil moisture storage (Sidle et al., 1995)
Water table elevations (e.g. Detty and McGuire, 2010)
Headwaters Workshop, February 25, 2011
Empirical observations of nonlinear rainfall-runoff
response of 4 hillslopes: subsurface stormflow
N=4
Weiler, M., J.J. McDonnell, H.J. Tromp-van Meerveld and T. Uchda, 2005, 112: Subsurface Stormflow, in
Encyclopedia of Hydrological Sciences, Anderson, M.G., ed., John Wiley & Sons, Ltd., v. 3, p. 1719-1732.
The small catchment scale
 A scale integrating hillslopes, riparian areas,
ephemeral, intermittent and perennial stream reaches.
 A complex range of runoff generation processes –
activation of which varies in both time and space.
 Subsurface storm flow
 Overland flow (Infiltration excess or saturated overland
flow)
 Variable source areas
 Direct precipitation, etc…
Headwaters Workshop, February 25, 2011
Quantifying antecedent soil moisture storage
(example from North Carolina Piedmont)
 ASI – antecedent soil
Soil Moisture (%)
-5
moisture storage index.
 Integrated measure of
 Using soil moisture from
multiple probes installed
in top ~ 1 m of soil.
35
0
10
20
Depth (cm)
volumetric soil moisture
prior to a storm.
15
Clay loam
Seasonal change Ksat= 181cm/day
30
40
50
60
70
80
90
100
Clay
Ksat = 1 cm/day
55
Example 1:
Hubbard Brook
Experimental
Forest, USA
Clear threshold in rainfallrunoff response with:
(a) antecedent soil
moisture storage + storm
size.
(b) water table elevation.
Detty and McGuire (2010),
WRR, VOL. 46, W07525, 15
PP.,
2010 doi:10.1029/2009WR00
Example 2: Piedmont region of North Carolina
40
• 2 different hydrologic landscapes
(steep, well drained hillslopes v.s. flat
hillslopes with a shallow expanding
clay).
• All show a clear threshold in storm
response as a function of:
i) ASI + rainstorm total precipitation
ii) normalized riparian groundwater
depth.
Headwaters Workshop, February 25, 2011
Streamflow (mm)
• 5 small headwater catchments
30
y = 0.4711x - 126.64
R² = 0.9048
20
10
0
150
200
250
300
350
ASI + rainstorm total precipitation
Understanding this threshold response
 More complicated, an active
Detty and McGuire (2010):
suggest a source-area
threshold.
 Transition between runoff
generated in the near-stream
zones (below threshold) and
increasing hillslope
contributions (abovethreshold).
Streamflow (mm)
area of research….
40
30
y = 0.4711x - 126.64
R² = 0.9048
20
10
0
150
200
250
300
350
ASI + rainstorm total precipitation
• Increased connectivity of
saturated subsurface areas above
the threshold, due in part to
transmissivity feedback.
Headwaters Workshop, February 25, 2011
Implications for headwater management
 Need for estimating soil water storage and catchment-averaged
water table depths into assessment of headwater systems (Detty
and McGuire, 2010).
 Need to incorporate this response in our models (Detty and
McGuire 2010). Can this threshold response be captured by
current catchment-scale models?
 Do we see a similar response in all sorts of headwater systems?
 Could quantifying the threshold for individual catchments act as
a simplified model for management use?
 Implications for landuse and climate change: the latter
potentially impacting both antecedent storage and storm size.
Headwaters Workshop, February 25, 2011
2) Frameworks for catchment classification

‘The concept of Hydrologic landscapes’ (Winter, 2001)

‘On the need for catchment classification’ (McDonnell and
Woods, 2004)

‘ A framework for broad-scale classification of hydrologic
response units…’ (Devito et al. 2005)

‘Mapping first –order controls on streamflow from drainage
basins…’ (Buttle, 2006) –

Review of classification systems….(Dahl et al. 2007)
Headwaters Workshop, February 25, 2011
What do these frameworks offer?
1.
Organizational frameworks with which to classify catchments
and their hydrologic behaviour.
2.
All suggest we integrate components of the hydrologic
system: e.g. surface water and groundwater.
1.
Can be applied at any scale of interest.
2.
A basis for determining: where, when, under what conditions
and at what scale specific environmental factors (climate,
surface and subsurface topography, soil depth, cover type,
distribution) are most important …this remains unanswered..
Headwaters Workshop, February 25, 2011
Example 1: Devito et al. (2005)
They asked : “…Which landscape feature should be considered first?...”
 Consideration of environmental factors in this specific order (decreasing
spatial scale), …to determine the relative influence on controlling
hydrologic processes, scales of interactions and budgets…”
A. Climate
B. Bedrock geology
C. Surficial geology
D. Soil type and depth
E.
Topography and drainage network
 Boreal Plain –evidence that elevational differences (topgraphy) is not necessarily
the most important variable. Variation in areal definition of a catchment when
based on topography or surficial geology.
Example 2: Developing models for ungauged basins
Soulsby et al. (2006) J.of Hydrol. 325, 197–221
 Development of a conceptual model of catchment hydrological
functioning based upon dominant soil cover and topography.
Example 3: Linking to watershed management
• Falls Lake Reservoir, Raleigh-Durham-Chapel Hill, North Carolina. Source of
drinking water for > 550,000 people in the Triangle Area).
• Impaired by high nutrient and sediment concentrations.
• Red
•
areas: a
hydrologic landscape
defined by topography
and soils.
• High storm runoff
likely to occur due in
part to shallow
expansive clays that
prevents infiltration.
• Areas more
susceptible to flash
flooding, pollutant
transport into streams,
lakes, wetlands.
Falls Lake
Reservoir
Headwaters Workshop, February 25, 2011
Example 2: Linking to watershed management
Read Areas:
Projected to
naturally
generate
large
differences in rainstorm runoff,
particularly
during
winter
storms, due in part to shallow
expansive clays (Triassic Basin)
that prevent infiltration of
rainwater to depth.
L1
(white)
HL2
(red)
Headwaters Workshop, February 25, 2011
Summary
 Experimental studies at hillslope and small catchment scales are providing
new insights into how streamflow changes as a function of environmental
conditions (e.g. storm size and antecedent moisture conditions) and
environmental factors (soils, topography, geology).
• Do all types of catchments exhibit threshold response? What is the physical
explanation, and how might this understanding lead to better predictive
hydrologic models?
• Future climate change may indeed affect rainstorm size, intensity and
frequency.
Although there are great uncertainties in future climate,
understanding the sensitivity of streamflow to these variables provides a
foundation for planning for future change.
•
Classification frameworks – offering a basis for conceptual modeling with
immediate relevance to headwater system management and planning.
Headwaters Workshop, February 25, 2011
Acknowledgements
 North Carolina State University, Dept. of Forestry and
Environmental Resources, College of Natural Resources.
 US Forest Service, Southern Global Change Program., Raleigh,
NC.
 Canada Research Chair Program; Canada Foundation of
Innovation; Ontario Ministry of Research and Innovation,
Nipissing University.
Headwaters Workshop, February 25, 2011