streamflow generation: an introduction · 2 the question: why does stream- runoff behave the way it...
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Quantitative Elements of Physical Hydrology
Streamflow Generation:An Introduction
Streamflow Generation:An Introduction
© John F. HermanceJanuary 28, 2007
Contact information:Jack HermanceEnvironmental Geophysics/HydrologyDepartment of Geological SciencesBrown UniversityProvidence, RI 02912-1846Tel: 401-863-3830e-mail: [email protected]
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The Question: Why does stream-runoff behave the way it does?
The Thesis: Historically, streamflow shows a strong correlation with precipitation. Knowing the nature of this relationship, we can predict stream
discharge from known or predicted precipitation.
© John F. Hermance
Compare Stream Discharge (Q) to Precipitation (P).
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Changes in the streamflow of the Pawcatuck River for aspecific precipitation event.
Example of a single "event".( We want to explore “cause & effect” in a watershed system.)
© John F. Hermance
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A classic problem in the "response" of physical systems.
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The transfer function of a system allows one to predict the expected output process due to a specified input process.
Changes in the streamflow of the Pawcatuck River for a precipitation event.
A precipitation eventon October 9 ...
© John F. Hermance
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Changes in the streamflow of the Pawcatuck River for a precipitation event.
… causes a streamflow peakon October 11 .
© John F. Hermance
© John F. HermanceJanuary 28, 2007
Quantitative Elements of Physical HydrologyQuantitative Elements of Physical Hydrology
Why do these systems behave theway they do?
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What are the fundamental relationships between precipitation and streamflow
in a watershed?
© John F. Hermance
© John F. HermanceJanuary 28, 2007
Quantitative Elements of Physical HydrologyQuantitative Elements of Physical Hydrology
A Review of the Water Cycle Elements.
Skip to Dynamic interaction . . .
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Here we look at the composite effect of lateral flow to a stream.
© John F. Hermance
© John F. Hermance
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A schematic view of water pathways.
© John F. Hermance
We want to look in detail ata single 2D “slice” through
this system.
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(When discussing the following paradigms, it is important to keep
in mind that whatever water enters the stream from its side is
carried away by flow.)
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Review of the connectivity of the watershed elements.
An Inventory of Watershed Elements
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An Inventory of Watershed Elements
© John F. Hermance
Infiltration and direct recharge Infiltration and direct recharge
An Inventory of Watershed Elements
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ThroughflowThroughflow
An Inventory of Watershed Elements
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InterflowInterflow
An Inventory of Watershed Elements
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Seepage (springs) Seepage (springs)
An Inventory of Watershed Elements
© John F. Hermance
Return FlowReturn Flow
An Inventory of Watershed Elements
© John F. Hermance
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Overland Flow(Horton & Saturated)
Overland Flow(Horton & Saturated)
An Inventory of Watershed Elements
© John F. Hermance
Groundwater Flow(in saturated zone)Groundwater Flow(in saturated zone)
An Inventory of Watershed Elements
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Baseflow:Groundwater flow
through the saturatedzone to streams
Baseflow:Groundwater flow
through the saturatedzone to streams
An Inventory of Watershed Elements
© John F. Hermance
An Inventory of Watershed Elements
WatertableMoundingWatertableMounding
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In some cases there can be substantial “bank storage”.In some cases there can be substantial “bank storage”.
An Inventory of Watershed Elements
© John F. Hermance
The Principal Watershed Elements
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© John F. HermanceJanuary 28, 2007
The Dynamic Interaction ofWatershed Elements:
Transverse Contributions to Streamflow
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We next look at the time and space sequencing of precipitation, surface runoff, groundwater flow
and streamflow generation.
© John F. Hermance
© John F. Hermance
(Note: No precipitation for anextended period.Groundwater table in"equilibrium" with streamlevel.)
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(Note development of “bank storage”.)
(Note development of “bank storage”.)
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© John F. HermanceView sequence again
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© John F. Hermance
This is only one of many scenarios for the time-space interaction of precipitation and runoff.
© John F. Hermance
A more typical “initial condition” for astormflow event follows.
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© John F. Hermance (Discuss)
The Thesis: Historically, streamflow shows a strong correlation with precipitation. Knowing the nature of this relationship, we can predict stream
discharge from known or predicted precipitation.
© John F. Hermance
Compare Stream Discharge (Q) to Precipitation (P).
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Longitudinal Stream Development
© John F. HermanceJanuary 28, 2007
Next we look at the composite effect of longitudinal flow to a stream along its axis.
© John F. Hermance
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© John F. Hermance
A schematic view of water pathways.
© John F. Hermance
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We want consider how these discrete “slices”provide an aggregate
streamflow.
© John F. Hermance
Surface runoff and baseflowact in parallel to feed
streamflow.
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This lateral contribution is comprised of local Horton and saturated overland flow, return flow from seepage, and baseflow (groundwater).
© John F. Hermance
Use this symbol to denote thesum total of all surface runoff
and baseflow deliveredby this slice.
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Other “slices” or 2D elementsalso contribute to
streamflow.
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Which integrates to the composite
aggregate stream discharge, Q
© John F. Hermance
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1 flow unit
6 flow units
Plan view illustrating the longitudinal integration of lateral inputs to streamflow.
The thickness of the arrow is used to denote the local magnitude of stream discharge.The basic idea is that streamflow is generated by the integrated contributions of surface runoff and baseflow along its length.
© John F. Hermance
Summary:The Paradigm: Longitudinal stream development is the composite effect of lateral flow to a stream along its axis. We saw an example of lateral input from a discrete 2D element. We assumed that each 2D “slice” provides a discrete contribution to the total streamflow. The superposition of transverse surface and subsurface flow from these discrete slices is what we term the “longitudinal integration of lateral inputs” to generating and sustaining streamflow.
© John F. HermanceJanuary 28, 2007
Streamflow discharge (Q) progressively increases downstream due to lateral inflow from surface runoff, interflow and groundwater base flow.
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A Caveat: Longitudinal stream attenuation
Note: Streams can lose water along their channel, or reach, as well as gain water.
© John F. Hermance
End of Presentation(Streamflow Generation: An Introduction)
End of Presentation(Streamflow Generation: An Introduction)
Quantitative Elements of Physical Hydrology
© John F. HermanceJanuary 28, 2007