[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Swarm-Modelling] Swarm and Braided Rivers
From: |
Crile Doscher |
Subject: |
[Swarm-Modelling] Swarm and Braided Rivers |
Date: |
Thu, 16 Dec 2004 15:55:46 +1300 |
Having recently gotten a basic Swarm model running (with a lot of help from the
Support
list), I think it's time I migrated questions over to this list as I move on to
refinements. So,
hello all! My interest is braided rivers, rivers with either sand or gravel
riverbeds, with
typically wide floodplains and relatively steep slopes. Since the bed is made
up of
movable material, these sands and gravels are moved around by the flowing
water, and
in the process form multiple channels (hence the name braided). You can see
these
processes at work next time you're at the beach and come across water flowing
over the
sand. An interesting aspect of these rivers is their scaling properties.
Regardless of
whether it's a trickle of water flowing over sand or the Bhramaputra River (a
rather large
river), the behaviour seems to be the same: the channels tend to follow a power
law
distribution in both time and space (not unlike turbulence or earthquakes).
There is
debate about why this should be (and it's certainly not the only natural
phenomenon that
seems to do this) and I see Swarm as an ideal environment for some hypothesis
testing.
There are some feedback loops affecting how the river channels evolve, namely,
the
water moves sediment from certain places and deposits it elsewhere, which in
turn
affects where the water flows, which affects the sediment, etc. It's a classic
example of
independent agents following (simple) local rules with global behaviour
emerging from
the interactions (or so I claim).
I currently have a model in which the agents are finite volumes of water that
flow over a
cell surface containing elevation values. The agent moves about by going in
the direction
of steepest slope to the neighbouring cells. A next step is to incorporate the
ability of the
water agent to pick up sediment in certain conditions and deposit it somewhere
else
under different conditions. Then it gets a bit tricky. There will likely be
multiple agents in
certain cells which are fatal (given Discrete2d) but I'm at work on that. I'm
sure
everyone's Swarm model has unique requirments, and here are some of mine.
One theory I'd like to test is that braided rivers are hiearchically
structured, i.e. what
happens at one scale can constrain what happens at another scale. Is it
possible to
have multiple cell surfaces, each with its own resolution (cell size) living in
the same
space such that linkages can be set up between the scales? The nature and
direction of
the linkages are things to be investigated. What it might mean in effect is
that before a
water agent can move to a particular cell, it might need to check with what's
happening at
another scale (or scales) before doing so.
Another challenge - anyone who's watched a river flow will recognise that
different
parts of the river flow at different velocities, which gets us into the area of
asynchronus
updates. Much of my preliminary reading of the Swarm documentation led me to
believe
that this is possible and is one of the main attractions of using Swarm. Does
anyone
have any direction on how to carry that out?
My apologies if that's been a rather long-winded buildup and thanks for any
responses.
Crile
Dr Crile Doscher
Natural Resources Engineering
Lincoln University
Canterbury
New Zealand
- [Swarm-Modelling] Swarm and Braided Rivers,
Crile Doscher <=