Author Topic: Bifurcation ratio and drainage density  (Read 7795 times)

international

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Bifurcation ratio and drainage density
« on: October 14, 2009, 10:48:13 PM »
Hi everyone
I'm getting a little confused with bifurcation ratios and I would appreciate some help. If a basin has a low ratio then there is more chance of flooding. Is this because if the ratio was higher then the water is more spread out across the orders of the streams?

In addition, is it possible that a drainage basin could have a high density and a high bifurcation ratio? If this is the case then on the one hand, the basin would be subject to flooding due to the amount of channels that would move water to the main channel but on the other hand, there could be plenty of streams in which to accommodate the water.

Any advice would help a confused geog teacher.

Thanks ???


Graham

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Re: Bifurcation ratio and drainage density
« Reply #1 on: October 15, 2009, 04:58:11 AM »
River networks- Bifurcation Ratios

In the application of the Strahler stream order to hydrology, each segment of a stream or river within a river network is treated as a node in a tree, with the next segment downstream as its parent. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream. Streams of lower order joining a higher order stream do not change the order of the higher stream. Thus, if a first-order stream joins a second-order stream, it remains a second-order stream. It is not until a second-order stream combines with another second-order stream that it becomes a third-order stream. As with mathematical trees, a segment with index i must be fed by at least 2i ? 1 different tributaries of index 1.

To qualify as a stream a hydrological feature must be either recurring or perennial. Recurring streams have water in the channel for at least part of the year. The index of a stream or river may range from 1 (a stream with no tributaries) to 12 (the most powerful, river, the Amazon, at its mouth). The Ohio River is of order eight and the Mississippi River is of order 10. 80% of the streams and rivers on the planet are first or second order.

If the bifurcation ratio of a river network is low, there is a higher chance of flooding, as the water will be concentrated in one channel rather than spread out, as a higher bifurcation ratio would indicate. The bifurcation ratio can also show which parts of a drainage basin is more likely to flood, comparatively, by looking at the separate ratios. Most British rivers have a bifurcation ratio of between 3 and 5. [2
Assistant Headteacher.
Cardinal Newman Catholic School, Hove
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international

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Re: Bifurcation ratio and drainage density
« Reply #2 on: October 16, 2009, 02:40:27 AM »
Thanks Graham. I'm more or less okay with the concept and relation to flooding. Many other features factor into the equation and bifurcation and density cannot be used alone when considering flooding within a basin.


Graham

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Re: Bifurcation ratio and drainage density
« Reply #3 on: October 17, 2009, 09:36:05 AM »

That's absolutely correct as it is only one oif the factors.
Assistant Headteacher.
Cardinal Newman Catholic School, Hove
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GASQM 'Centre of Excellence'

international

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Re: Bifurcation ratio and drainage density
« Reply #4 on: October 18, 2009, 11:57:08 PM »
Sorry, I shouldnt think too much about these issues, especially on a sunday evening, but I was further contemplating the bifurcation ratio. In terms of the explanation about water being spread out consider this example: a basin has 21 first order streams and 3 second order streams. This produces a br of 7 which is high and this basin should not be expected to flood as much as another basin which could have 21 first order stream and 15 second order streams and subsequently a br of 1.4. In terms of the water being spread out though, a higher ratio would mean potentially a large number of streams providing water for a significantly fewer amount of streams in the next order whilst a smaller br would mean a relatively large amount of streams in the next order to receive that water, (15 streams to receive the water from 21).

Wouldnt this create a situation that with a large number of streams of the next order to accommodate the water, the precipitation that a basin receives would be channelled quickly to the main channel and create flooding?

Sorry but it is the first time I have taught rivers.

Many thanks again

international

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Re: Bifurcation ratio and drainage density
« Reply #5 on: October 21, 2009, 01:44:34 AM »
Bump.

Hope Ive made sense!

 

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