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Workshop Report

From new descriptions of catchment form and function to new model blueprints

Conveners: Jeff McDonnell and Kellie Vache
Workshop Motivation

Catchment hydrology is at a theoretical impasse. Our best models are predicated on porous media flow theory based on Darcy's law and Richards equation, yet we observe non-Darcian flow in the soil cores that we collect (macropores), hillslopes that we dissect (networks of pipes, cracks) and streams we gauge (where flux exceeds what hydraulic conductivity measured at a point would predict). The old water paradox-the fact that catchments store water for considerable periods of time and then release it promptly during rain and snowmelt events (as indicated by chemical signatures)-has caused the field to confront directly its theory vacuum. This CUAHSI vision workshop will tackle this issue and produce a monograph aimed at clearly defining the theory impasse and potential ways forward.


1. Understanding heterogeneity: form and function

The workshop will first address how we might develop new and efficient ways of characterizing heterogeneity, or "form", from point to hillslope to catchment scales. We will examine how we can learn from the patterns and how we might distil complexity into simple functional representations thereby linking form with function. Presentations and discussions will question the role of the functions both hydrological and ecological. We expect that exploration of these questions and new hypotheses testing may be the pathway to discover "laws" that govern hydrological systems-the foundation of a "theory" of hydrology.

2. Dealing with heterogeneity: new model blueprints

The workshop will next address the need for numerical and practical tools that can incorporate the heterogeneity of landscapes for making predictions in gauged and ungauged basins, the test beds of our understanding. These presentations and discussions will acknowledge that the modeling blueprint must acknowledge and do justice to both the form and function and emergent behavior resulting from this (e.g. thresholds and other forms of nonlinearity). Our discussions will focus on the need to develop coherent language and technologies so that advances in knowledge of form and function (heterogeneity) can be naturally and easily absorbed in predictive capability. Deficiencies in predictive capability can then inform and guide future process studies aimed at improved functional representations.

3. Learning from historical information

While the first two parts of the workshop will be largely "bottom up", the third part of the workshop will explore top-down approaches (e.g. data-based, or patterns-based methods). These top down strategies will help us to make full use of available physical, chemical and isotopic data for deciphering patterns. Interpretation of these data-based and patterns-based processes may be another pathway to learn something about the system.

Workshop Style

The workshop will be intentionally small in number. We expect it to be fully participatory where everyone's ideas are valued and sought. While highly informal, the workshop is outcome based, where a working document will be outlined on Day 3 for post-workshop manuscript writing. The deadline for submission of this manuscript to CUAHSI is August 31, 2004.