# Presentation: 477469

## Hydrogeophysics at the NCHS

- Science Questions that can be addressed?
- Hydrogeophysical Challenges
- How can hydrogeophysics at the NCHS  contribute to Synthesis?

- Common theme in contemporary hydrology:
- Subsurface, surface and atmosphere are coupled
- Hydrogeophysics: monitor and characterize subsurface properties and processes over a wide range of spatial and temporal scales

## Hydrological synthesis requires understanding the states, stocks, residence time, fluxes, and transformations of water, sediments, contaminants, and nutrients through the full vertical range (from soil to atmospheric column), and spatially over watersheds.

## Near-surface geophysical methods offer potential for providing information about hydrogeological properties and processes over various spatial and temporal scalesHowever, there are still many obstacles that hinder the routine use of geophysics for watershed characterization:

-  Integration techniques (how to handle scale disparities and deal with uncertainty and non-uniqueness issues in a rational manner)
-  Petrophysical relationships (link the indirect and direct measurements)
-  Limitations (communicate present and future abilities and limitations of techniques)

## Geophysical Measurements are

- 1) Indirect – measure geophysical attributes, not hydrogeological parameters
- 	Needed: Theoretical basis for interpreting measurements
- 2) Volume averaged, typically with a different support scale than most hydrological measurements
- 	Needed: scaling and integration techniques
- 3) Sensitive to several different hydrogeological properties
- 	Needed: integration techniques to assist with non-uniqueness

- Example:  Qualitative relationships between seismic P-wave velocity and Hydrogeological Properties
- (Tatham and McCormack, 1993)

## Advantages of Using Geophysical (G) Data in addition to Hydrologic (H) data

- Minimally invasive, Multi-dimensional, Varied spatial resolution

*Hubbard and Rubin, 2005*

## Acquisition Geometries for Different Scales of Investigations

- Acquisition Geometries for Different Scales of Investigations

**BOREHOLE****	****        CROSSHOLE                               SURFACE**

**LAB                                                                                                            AIRBORNE**

*Movie from A. Binley*

## Hydrogeophysical Investigations

- 	Water Table
- 	Hydrostratigraphy
- 	Top of Bedrock
- 	Fault/Fracture zone
- 	Fresh/Salt Water Interface
**2. PARAMETER ESTIMATION**
- 	Water Content
- 	Water Quality
- 	Lithology
- 	Porosity/Permeability
- 	Sediment Geochemical Parameters
- 	Fracture Zonation
- 	Spatial Correlation Structure
- 	Plume Moments
**3. HYDROGEOLOGICAL PROCESSES**
- 	Water infiltration
- 	Water quality
- 	Contaminant Migration
- 	Detecting transformations under natural or perturbed (i.e., biostimulation) conditions

## Common surface, crosshole and borehole geophysical techniques 

**Common surface, crosshole and borehole geophysical techniques **
**used to assist hydrogeological investigations**

- Hubbard and Rubin 2005

## Relative Applicability of different Geophysical Methods

- 0 = not considered applicable; 1 = limited use; 2 = used, or could be used, but not the best approach or has limitations; 3 = has potential but not fully developed; 4 = generally considered an excellent approach, techniques are well developed. **1 These applications are current topics of research*

- for Hydrogeological Investigations

- Hubbard and Rubin, 2005

## What is the degree of spatial organization within a river basin, how does it impact the water budget, and how can it be characterized? Can constitutive laws for the spatial organization in drainage basins be developed? 

What role does subsurface preferential flow play in the distribution of water at the watershed scale?

Are there effective governing equations for watershed-scale processes? If so, what are the key parameters in such equations, and what measurements are needed  over what spatiotemporal scales to quantify these parameters? How do parameterizations of processes scale from field plots to catchment to river basin scales?

What are the pathways by which recharge to groundwater occurs, and how do faults and bedrock structure impact the fluxes?

- What role does subsurface preferential flow play in the distribution of water at the watershed scale?
- Are there effective governing equations for watershed-scale processes? If so, what are the key parameters in such equations, and what measurements are needed  over what spatiotemporal scales to quantify these parameters? How do parameterizations of processes scale from field plots to catchment to river basin scales?
- What are the pathways by which recharge to groundwater occurs, and how do faults and bedrock structure impact the fluxes?

- Hydrologic Science Questions that require Advanced Characterization and Monitoring

## What role does deep soil water and groundwater play in land surface and climate processes, and how will climate variability impact groundwater resources? 

How do biogeochemical transport and transformations modulate the fluxes of nutrients, contaminants, and sediments to surface water in watersheds? 

How does climate variability effect soil moisture variability, and how does soil moisture impact climate? 

How do spatial and temporal variability of soil properties and land surface influence water budget at watershed scale? What are the critical space and time scales for measuring soil moisture and land surface properties?

How do vegetative processes modify atmospheric water content and subsurface soil/groundwater?

- How do biogeochemical transport and transformations modulate the fluxes of nutrients, contaminants, and sediments to surface water in watersheds?
- How does climate variability effect soil moisture variability, and how does soil moisture impact climate?
- How do spatial and temporal variability of soil properties and land surface influence water budget at watershed scale? What are the critical space and time scales for measuring soil moisture and land surface properties?
- How do vegetative processes modify atmospheric water content and subsurface soil/groundwater?

-  . . . beyond physical hydrology

## Example 1: Water balance in a natural, heterogeneous system

- Where is runoff generated?
- What role does groundwater play in
-   feeding streams and wetlands?
- How does bedrock influence the
-  volume, residence time, and fluxes of groundwater?
- What role does preferential flow play in governing subsurface transport?

- The Weatherley Catchment, North Eastern Cape, South Africa, Lorenz, 2003

## Hydrogeophysical imaging of critical structures 

- Hydrogeophysical imaging of critical structures

- Mapping depth to bedrock (Uhlenbrook et al., 2005)

- Mapping key interfaces and water table using GPR (Hubbard et al., 2001)

## Estimate Properties or Monitor Processes

- Hydraulic Conductivity (Hubbard et al., 2001)

- Change in saturation (Williams, 2002)

- Soil water content (Hubbard et al., 2005)

## How do physical, geochemical, and microbiological heterogeneities influence reaction rates and nutrient cycling at the watershed scale? 

- Example 2

## Geophysical Methods for biogeochemical studies

- Monitoring change in mineralogy and grain surface area associated with Fe-reduction during biostimulation (Williams et al., 2005)

## Hydrogeophysical Challenges

- Hydrogeophysical obstacles exist due to indirect nature, ambiguity, and scale of geophysical measurements:
- 	Key hydrogeophysical ohallenges associated associated with:
- Theoretical models
- Petrophysical Relationships
- Data integration
- scale issues relevant in all cases
- Most Hydrogeophysical research has been performed at small spatial scales – **there is little experience with quantitative hydrogeophysics at the watershed scale**

- Iterative Investigations

**Interpretation **
**and Theory**

## Hydrogeophysical challenge: 

- Integration methodology dependent on the objective and experience
- Approach: Deterministic or Stochastic

- statisticalcharacteristicsof structure

- scenarioprediction

- hydrologicmodel

- hydrogeol.data

- hydrogeol.propertyestimates

- geophys.data

- geophys.estimates

- Figure from Kemna, 2003

- Hydrogeophysical challenge:
- Integrating hydrogeological and geophysical information

## Key Hydrogeophysical Challenge: Petrophysical Models

- Many of the relationships that link geophysical measurements to hydrogeological parameters in unconsolidated, low-P, low-T environments are not well understood, non-unique; scaling unknown

- Moysey and Knight,
*WRR*, 2004

## How can hydrogeophysics at NCHS contribute to Synthesis?

## NCHS Partners

- NCHS partners:
- Are interested in developing geophysical watershed instrumentation observation platforms
- Have access to large datasets and are accustumed to large geophysical data acquisition campaigns
- Can assist in transferring the science developed at the NCHS to the observatories, via NCHS end-to-end demonstrations

## Working group: Watershed hydrogeophysical science

Goal
	Identify the current and future technological and scientific abilities and limitations

Membership
	Represent range of approaches, 
	experts in theory, instrumentation, field studies
	users (to define data needs)

- Goal
- 	Identify the current and future technological and scientific abilities and limitations
- Membership
- 	Represent range of approaches,
- 	experts in theory, instrumentation, field studies
- 	users (to define data needs)

## Working group: Watershed hydrogeophysical science

Deliverables
Roadmap that identifies existing methods or needed methods for watershed characterization, protocol for use
White paper on watershed characterization using hydrogeophysical approaches;
Knowledge transfer to HO;
promote technology and theory development (motivated by HO and synthesis needs), including single PI activities.

- Deliverables
- Roadmap that identifies existing methods or needed methods for watershed characterization, protocol for use
- White paper on watershed characterization using hydrogeophysical approaches;
- Knowledge transfer to HO;
- promote technology and theory development (motivated by HO and synthesis needs), including single PI activities.