The Highway Analogy to River Floodplain Relationship

The Highway Analogy is a concept in hydrology that was introduced by Junk, Bayley, and Sparks in their 1989 paper,  introduced in the paper "The Food pulse concept in river Floodplain systems."  The analogy compares studying a hypothetical study of a highway network by "non-terrestrials" which take the same approach to studying a highway network system how "terrestrials" (humans)  to studying river networks.   The interesting idea is that from far way in an aerial perpective the highway may look like a self contained system and objects flowing through the network.  The non-terrestrial may notice changes in vehicles per hour at any given point. They can study how highway geometry, number of lanes, interconnections effect the flow rate.  But if they looked further, looking at a detailed study of the objects in the system. The cars in the highway, they will see that there are many different types of vehicles.  With different symbiotic organism in the vehicles.  They would also notice that vehicles enter and leave the highway.  Following vehicles individual as they leave the highway they would notice that some, like large trucks would go to commercial area to deliver goods, or go to agricultural areas to pick up goods.  Other like passenger vehicles would go into different parts of town creating economic activities.  As the "non-terrestrial" zooms in and studies the highway more the way of theory of the highway will evolve from a network, to a force on the entire region with long term economic and production impacts.  You could even start to theorize that connectivity to this network, or access time to get from any part of the region to the the highways system may have a large impact on the land use and values of any area.

Turing this analogy around, and looking at how "terrestrials" study the rivers, we are on the verge of changing the way of thinking about a river and it's floodplain.  The river is a network that transports water, sediment, and nutrients.  We understand well how the water, sediments, and nutrients are put into the system through precipitation, runoff, infiltration, and springs.   We are starting to understand that the river is connected to the surrounding floodplain through hydrological connectivity.  This connectivity bring there nutrients, water, and sediment to the floodplain. This deliver is important in all the ecological cycles in the floodplain, and play a major force on the ecosystem of the floodplain.   The degree of connectivity then should dictate what ecosystem look like.  Studying this connectivity is in a way study trafic flow patterns throughout the whole street network, not just looking at highways but also surface streets.  Right now we study the river with inputs into the system, tributaries, streams, etc, but we are not looking at the overbank process, and the web of connectivity within the floodplain.  This web of connectivity is maybe the most important component in understanding the structure of the floodplain ecosystem.

References


Junk WJ, Bayley PB, Sparks RE. 1989. The Food pulse concept in river Floodplain systems. Can. Spec. Publ. Fish. Aquat. Sci. 106: 110-127.

http://www.nrem.iastate.edu/class/assets/aecl518/Discussion%20Readings/Junk_et_al._1989.pdf

The Flood Pulse Concept

Lotic Ecology (river, stream or spring ecosystems)  are dynamic places that have river-floodplain interactions that apply ecological forces on the system.  The most comprehensive approach to analyze the river-floodplain dynamics is the flood pulse concept developed by  Junk, Bayley and Sparks (Junk et al., 1989).  The big idea that came from their work is that rivers and their floodplains are integrated components of a single dynamic system.  That even though we think of them as two separate places they are components of the same system linked by strong hydrological and ecological interactions.  This means that the perceived border between a river's channel and it bank is not solid. It is porous and dynamic, allowing flows to overbank into the floodplain.   The major driving force in the concept is that the pulsing of river discharge, which in turns determines the degree of connectivity.  The discharge in a river is not constant and is continuously changing up and down, like the pulse of blood through a vessel.

This idea of a flood pulse is theorized by this paper as a major controlling force on the biotia in river-floodplains.  This means as the river pulses, leading to overbank processes, the water that connects the river channel to the floodplain bring nutrients and sediments into the floodplain.  This lateral exchange is important and often the dominent force in the nutrient cycles for some patches of the floodplain.  Water is a good solvent, so as it flows through a channel it carries dissolved and solid substances.  As the water over-banks the natural levee of a river, it will deliver not only the water carried in the flow, but aso the dissolved and solid substances.

References

Junk WJ, Bayley PB, Sparks RE. 1989. The Food pulse concept in river Floodplain systems. Can. Spec. Publ. Fish. Aquat. Sci. 106: 110-127.

http://www.nrem.iastate.edu/class/assets/aecl518/Discussion%20Readings/Junk_et_al._1989.pdf