Stanford University

Woods Seminar | Flow and Transport at Catchment Scales: New Approaches to an Age-Old Problem | Ciaran Harman, Johns Hopkins University

When:
Thursday, Feb 21, 2019 4:15 PM
Where:
Y2E2 Building, Room 299
More Info:
Woods Seminar | Flow and Transport at Catchment Scales: New Approaches to an Ag…
Audience:
Faculty/Staff, Students
Sponsor:
Stanford Woods Institute for the Environment

Abstract

Catchment hydrology has struggled to develop a unified approach to understanding and predicting the flow of water and the transport of solutes at catchment scales. Our current difficulty answering basic questions about flow and transport through shallow and deeper pathways, particularly in ungauged watersheds, arguably limits our ability to deliver the kind of predictions needed for water resource planning and regulation the over the long term, and across spatial scales. In this talk I will discuss this long-standing challenge, and two approaches to addressing it. One is to seek physically-meaningful ways of conceptualizing and mathematically representing flow and transport at catchment and large-grid scales. The other is to reframe the question entirely: perhaps in addition to asking “what is the hydrologic structure of the landscape?” we should also be asking “why is it so?”.

New process representations are needed that a) capture the integrated effect of un-observable internal structure without requiring us to resolve that structure explicitly, b) are physically meaningful, yet c) are parsimonious enough that they stand some chance of being inferable from available data. StorAgeSelection (SAS) theory has emerged as a powerful tool for both interpreting active and passive tracer data and making predictions about the movement of solutes in a variety of hydrologic settings. SAS is a generalization of transit time distributions that allows for time-variable fluxes through the system, and similarly provides a framework for capturing the integrated effect of internal structure and heterogeneity on transport. When used to interpret water tracer data (e.g. stable water isotopes), SAS functions have revealed details of the volume of internal storage turning over in the landscape, how rates of turnover differ between younger and older stores of water, and how that turnover changes as hydrologic conditions change. I will discuss advances we have made toward empirically observing SAS functions, connecting their properties to the physical structure of hillslopes, stream reaches, and small watersheds, and using them to anticipate the effects of climate change on agricultural nitrate delivery to streams.

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