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Stream Networks vs Watersheds/ Catchments

The reductionist view of watersheds as simple networks of streams focuses on surface waters.  See Reductionism vs Holism.  Not to besmirch a more enlightened view of stream systems, as understood by geomorphologists and biologists.

The reductionist view separates hydrology into surface water and groundwater, armed with analytical equations to explain and predict the behavior of both.

Hydrologists’ equations for surface flows are hyperbolic.  Those for groundwater are elliptical.  (Ponce personal communication 2009)

In between has been a (nearly) no-hydrologists’ zone for quite some time.

Rainfall to Groundwater applies an inherently holistic, systems perspective, that considers the netherworld of reductionist hydrology –

The unsaturated, or vadose zone that lies between the land surface and the water table.  The existing or, in many cases, potential “sponge”.

True of surface waters also, interflow through the vadose zone is subject to influence by living/ ecological systems.  

Ecohydrology.

Nonlinearity.

Novelty.  To stimulate and challenge us.

We can influence detention storage in watershed/ catchment vadose zones by influencing the .vegetation that catalyzes vadose zone ecology and ecohydrology.

That error of omission from reductionist hydrology – “seeing” only surface waters or saturated groundwater – blinds its proponents to opportunities to influence watershed aka catchment systems to better sustain groundwater..

Figure vs Ground considers how the cultural “East” emphasizes the space between the flowers in an arrangement.

It’s not clear to Verna how streams vs watersheds/ catchments plays out in the cultural “East”, but in the “West”, it seems implicit that most who ever think about watersheds at all (a select group in themselves) tend to think of them as stream networks, at best stream systems.

The “flowers within the space”, rather than grasping holistic interrelations between stream and watershed, especially catchment.

That is, in the cultural “West”, the focus tends to be on the streams – where runoff drains to, ignoring catchment uplands where the vast majority of precipitation initially lands.

The historical focus has been on Sink vs Source.

Rainfall to Groundwater emphasizes the Source.

Uplands, being far more expansive than the drainages they feed, receive the majority of precipitation.  

That’s a major reason why restoration of uplands detention functions can reap far greater benefits than just focusing on the drainages, including mountain meadows, which are essentially just floodplains.

But restoration of wetland detention functions is synergistic with uplands restoration.  We must strive for both to better sustain our groundwater and baseflow needs.

In fact, stream networks are vastly more complex than the standard network diagrams used to portray them, as useful as those portrayals may be to describing stream environments in relative fashion, for comparing gauge data, etc.

Prime example is the concept of stream order, which indicates the degree of branching in the hydrographic system at any point.

Click image to expand

Most recognizable example currently used is the Strahler system, followed by the Shreve system.   In both cases, headwaters tributaries are represented by 1, with order number increasing at each successive downstream confluence..

Useful indeed, yet misleading if we take such figures at face value.  If we go out onto the land and seek out those first order headwater streams we will doubtless be challenged to find a single source for the “1” initial tributary.  This is because those linear drainage patterns become bifurcated again and again, traced to their sources.  See Surface-Groundwater Systems in a Holistic Water Cycle.  

Another example of a conceptual tool that can canalize users’ perspectives/ paradigms to the extent that they literally can’t “see” what the landscape is showing them, not unlike hydrological engineering models..

Headwaters are not linear, they’re fractal.  

It is the very same problem as the classic fractal example – measuring the length of a coastline.  The length depends on the scale at which it is measured.  The closer down you drill in scale, the more nuanced the specific shape and length of the coastline becomes  . . . the more nooks and crannies appear to be measured, thus the longer that coastline becomes.

originals made by Avsa mixed by AcadacBritain-fractal-coastline-combinedCC BY-SA 3.0

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ProkofievGreat Britain Box, background color by V. Jigour, CC BY-SA 3.0

Furthermore, headwaters are classically considered to result from overland flow, yet in headwaters with intact vegetation and soils, overland flow is highly unlikely.  It is much more likely that sources of intact  headwater tributaries arise from initial infiltration, percolation and interflow through the vadose zone, until that flow reaches a topographic contour that brings it to daylight.

Again, it’s that surface water bias that misses this natural pattern that is so obvious if one actually gets out on the land when it’s raining.  And again, see Surface-Groundwater Systems in a Holistic Water Cycle.  

Can you see the watershed/ catchment for the streams???

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