Using Heat as a Tracer to Better Understand Unlined Conveyance Seepage in an Arid Climate
Natural groundwater infiltration is inherently difficult to quantify and predict, because it comprises a series of
processes that are spatially distributed and temporally variable across many scales. Unlined conveyances,
however, represent more of a controlled environment and provide an opportunity to quantify seepage processes at
resolution scales of meaningful interest to Reclamation.
An improved understanding of these spatial and temporal seepage dynamics can greatly increase conveyance and
system efficiency and the effectiveness of water supply operations modeling and decision support systems. A
useful byproduct of studying seepage is an improved understanding of potential conveyance-aquifer exchanges,
because vadose and saturated zone data is appropriately transferable to conceptual and numerical groundwater
model development. Conveyance seepage studies can inform agricultural management, groundwater modeling
and sustainability, and adaptive management of climate change. For context, at irrigation district scales,
conveyance seepage in California's semi-arid San Joaquin Valley commonly exceeds large groundwater pumping
Need and Benefit
Reducing seepage loss uncertainty improves:
• System reliability and accuracy of planning and modeling, and the effectiveness of decision support systems;
• Conveyance management, including rehabilitation, reconfiguration, and other improvement efforts;
Groundwater sustainability management, managed aquifer recharge (MAR), and water supply reliability and
climate change analyses.
The scope of this proposal is the data collection and project definition required for a project that would use a
combination of in-canal thermal data collection and supporting numerical modeling to determine seepage in a
major unlined irrigation canal in an arid environment. Data from multiple sources would be needed to guide
appropriate placement of new temporary instrumentation in the canals and for the construction and calibration of
a numerical seepage model. These include: three dimensional canal geometry; surficial geology; shallow
stratigraphy with a conceptual depositional model; soil hydraulic properties; groundwater conditions; parcel
boundaries; and historical climate and operational data.
With a conceptual framework resulting from this proposal, and on approval of a full proposal, USGS would then
instrument the unlined canal network with newly developed, multi-depth, continuous temperature and
pressure-logging probes, aligned in transects perpendicular to flow and using newly refined installation methods.
With the aid of open-source software, USGS would develop and calibrate a flow model to quantify hydrologic and
operational relationships governing seepage. The model and data would be shared and used locally, and the
methods would be documented and made available across Reclamation.
By using heat as a tracer of flow, point- and transect-specific temperature data will be collected and input to the
supporting numerical model, and time-series analysis methods will be used to determine the range and
probabilities of seepage distributions based on the observed hydrology (at least 1 irrigation season). The flow
model will help lower seepage uncertainty and assist in predicting seepage.
Tools will include:
• VS2Di, a free, open source, windows-based software that models water, heat ,and multiple solute flow in
variably saturated porous media in two dimensions. Once the appropriate data are collected and a conceptual
model constructed, USGS will create a numerical model in VS2Di framework to relate heat to flow and to solve
Richard's equation using a high density of calibration points. The model will involve fairly high resolution canal
stage, meteorological, soil property, and heat and stage observation data. Additional model development detail,
theoretical background, and calibration and sensitivity analysis strategies will be included in the full proposal.
• Hydrus 1D is, similarly, a free, open source, windows-based software that models water and heat ,and multiple
solute flow in variably saturated porous media in one dimension. Hydrus can be used very efficiently for error
checking and model debugging of aspects of the two-dimensional modeling, and will likely have features to
supplement analyses made in VS2Di.
The selected field equipment and technology will include:
• Robust, low-profile design, multi-depth temperature profiling probes and housing fitted with micro pressure
transducers. USGS designs custom probes and housings for the purpose of investigating infiltration and to support
many types of surface water-groundwater interaction studies. The probes continuously and wirelessly log
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