April JamesCanada Research Chair – Watershed Analysis and Modeling

Department of GeographyNipissing 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 rainfall-runoff 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

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.

N = 4

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 flowOverland flow (Infiltration excess or saturated overland

flow)Variable source areasDirect precipitation, etc…

Headwaters Workshop, February 25, 2011

Quantifying antecedent soil moisture storage(example from North Carolina Piedmont)

ASI – antecedent soil moisture storage index.

Integrated measure of volumetric soil moisture prior to a storm.

Using soil moisture from multiple probes installed in top ~ 1 m of soil.

Clay loam Ksat= 181cm/day

ClayKsat = 1 cm/day

Seasonal change

Soil Moisture (%)

Dep

th (

cm)

Detty and McGuire (2010), WRR, VOL. 46, W07525, 15 PP., 2010doi:10.1029/2009WR008102.

Example 1: Hubbard Brook Experimental Forest, USA

Clear threshold in rainfall-runoff response with:

(a) antecedent soil moisture storage + storm size.

(b) water table elevation.

Example 2: Piedmont region of North Carolina

• 5 small headwater catchments

• 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

Understanding this threshold responseMore complicated, an active

area of research….

Detty and McGuire (2010): suggest a source-area threshold.

Transition between runoff generated in the near-stream zones (below threshold) and increasing hillslope contributions (above-threshold).

Headwaters Workshop, February 25, 2011

• Increased connectivity of saturated subsurface areas above the threshold, due in part to transmissivity feedback.

Implications for headwater managementNeed 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. ClimateB. Bedrock geologyC. Surficial geologyD. Soil type and depthE. 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 basinsSoulsby 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

• 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.

•

Headwaters Workshop, February 25, 2011

• 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.

Example 2: Linking to watershed management

Headwaters Workshop, February 25, 2011

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)

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