Runoff Generation in Forested Watersheds- A Half-Day Shortcourse

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Runoff Generation Presenter: Jeff McDonnell, Richardson Chair in Watershed Science, Oregon State University
Length: 9 parts, 3 hrs, 1 min and 16 s

       Topics:

       Part 1

Runoff Generation in Forested Watersheds

Introductions

Background

Benchmark papers

Good basic material

Advanced material

Journals you should consult...

Basic question that will be addressed

Traditional forest hydrology

Problems with the paired watershed approach

What this course will address

Mechanisms -our focus

Why these flow pathways and mechanisms are important

Water residence time is important

What we will and will not cover

       Part 2

Hillslope and watershed hydrology

Experimentalist and Modeler

Shortcourse outline

Example locations

Runoff Generation Overview

This section

Our History

Runoff generation at a point depends on

Storm characteristics and watershed runoff

Natural conditions for infiltration excess overland flow

Other factors that promote IEOF

READ

       Part 3

Hydraulic conductivity of some materials

Hydrological pathways

Hewlitt and Hibbert's, 1967 VSAC

SOF country

Saturated areas: we can estimate based on topography

Saturation overland flow

Spatial and temporal dynamics

Subsurface stormflow

       Part 4

How this might happen

But, also can be highly preferential

Dominant processes of hillslope response to rainfall

Model conceptualization of these processes

Proccess assumptions

3D Diagram

Plot Scale

This section

Plot scale: e.g. Inceptisols

What changes with depth

Depth function

Drainable porosity

       Part 5

Depth Function

Drainable Porosity

Ksat

But don't forget....

Soil profiles and cone penetrometer

The plot scale simplified

Pores

Network-like

If Darcy were alive today...

How infiltration really works

Infiltrations in macroporous soils

Classification of macropores

If we were to dig a pit

In other words

Macropores: engineers knew about this > 100 years ago

Observations

       Part 6

Observations

Plant Roots

Hillslope Scale

This section

From vertical to lateral flow

Vertical to lateral

Surface and bedrock topography

Hillsope trenching

Surface and bedrock topography

Flow distribution across the trench

Transient saturation: Spatial pattern 5mm

Transient saturation: 9mm

Transient saturation: 16mm

Transient saturation: 29mm

Transient saturation: 50mm

Transient saturation: 59mm

Transient saturation: 61mm

Threshold effects

Threshold effects- a common observation

       Part 7

Fill and spill behavior

Visualizing these processes

Or, if a 2-layer system...

Or, if a 2-layer system cont.

Equals transmissivity feedback

Back to our photo...

Back to transmissivity feedback

Pipeflow

We see thresholds for lateral pipeflow also...

Wherever we trench, pipeflow dominates

Transient water table drives the pipeflow

We've known about complexity for a long time

Catchment Scale

This section

Soil moisture - Wet

Soil moisture - dry

Terrain relationships

       Part 8

Threshold Responses

Back to the soil moisture diagram

Threshold Responses cont...

How catchment units sequence

Why this is important

Another way of looking at this

It's not continuous

Or, looking at this geochemically

Discrete units that connect and disconnect

From geographic source to time source

The reality

The old water paradox

Not a new idea

Stable Isotopes: hydrological tool

       Part 9

Two-component hydrograph separation

Time source of water during events

How old is the old water?

A recent GEOREF search

Residence time methods

Convolusion integral

Mean residence time

Some reported mean residence times

Watershed Model

Summary

Basic question that we addressed

One proviso before ending

REA: Something to keep in your mind

REA: something that you can determine

Hillslope and Watershed Hydrology

Shortcourse Summary

For a more extended virtual course...