From Urbanization to Erosion

14 11 2008

We are becoming more aware of the harmful effects of urbanization as we proceed with our enviromental design education.  But in this blog I want to focus on researching some effects that I did not already know.  Mainly I will discuss erosion; its causes and effects.

Main Entry:
erode           Listen to the pronunciation of erode
Pronunciation:
\i-ˈrōd\
Function:
verb
Inflected Form(s):
erod·ed; erod·ing
Etymology:
Latin erodere to eat away, from e- + rodere to gnaw — more at rodent
Date:
1612
transitive verb1: to diminish or destroy by degrees: a: to eat into or away by slow destruction of substance (as by acid, infection, or cancer) b: to wear away by the action of water, wind, or glacial ice <flooding eroded the hillside> c: to cause to deteriorate or disappear as if by eating or wearing away <inflation eroding buying power> 2: to produce or form by eroding <glaciers erode U-shaped valleys>intransitive verb: to undergo erosion <where the land has eroded away>
erod·ibil·i·ty           Listen to the pronunciation of erodibility \-ˌrō-də-ˈbi-lə-tē\ noun
erod·ible           Listen to the pronunciation of erodible also erod·able \-ˈrō-də-bəl\ adjective
Focusing on erosion as the result of water, wind, or glacial ice, I ask what does urbanization, urban spawl, and other patterns of environmental degradation have to do with erosion.  It is just that, we are becoming informed of the negative effects our actions today have on the environment and we have seen an increase in the frequency of natural disasters like hurricanes and global warming.  The changes in weather patterns have made way for more erosion because it is primarily caused by temperature, stom frequency, and run-off.
Also when humans settle, build, cut down trees, plant crops, or cultivate a particular piece of land, they increase the rate of erosion.  Also a high density of infastructure promotes higher levels of erosion.  All of this is important because its effects can affect us.  It is a cycle that must be broken.  Some effects include the loss of farmland, degradation of fertile soil.  I came across a more detailed reference on the effects of erosion (http://www.fao.org/docrep/t1765e/t1765e0a.htm):

ECONOMIC EFFECTS OF EROSION

1. On-site losses in eroded areas: affecting farmers

• Losses of water, fertilizers and pesticides
• Immediate production loss

– in regional terms: 2 to 10%: compensation possible through inputs
– in local terms: 2 to 50% = individual disaster = loss of profit margin

• Loss of arable land

– in world terms: 7 to 10 million ha per year
– in regional terms: 2 to 5%
– in individual farm terms: as much as 20 to 100%

It would take 200 years to destroy all arable land

• Long-term productivity loss = SOIL MEMORY

Reduced depth of topsoil
Reduced water and nutrient storage
Reduced effectiveness of rain and inputs
Reduced economic viability = soil depletion

CONCEPT OF SOIL LIFE-SPAN

2. Off-site – or downstream – damage: affecting townspeople

• Deterioration in water quality

pollution of rivers, death of fish, silting up of reservoirs, cost of dredging harbours

• Increase in suspended load (SL)

higher costs for drinking water

• Flooding of inhabited areas

mud flows, sanded up ditches

• Rise in peak flows of rivers

destruction of structural works, bridges, etc.

3. Major consequences for erosion control

Erosion on deep soils causes only off-site damage, but barely affects yields
Erosion on thin soils causes rapid falls in yields

Choice of an economically viable erosion control policy:

RML and SPR on degraded soil bring little improvement in yields, but do reduce sediment transport

SWC reduces soil loss from fields, conserves soil, but does not improve its fertility

LH

is concerned primarily with productive land
improves yields

by restoring its fertility
reducing runoff
increasing plant cover and rooting depth

indirectly or in the long-term reduces peak flows and sediment transport by rivers

CONCLUSIONS

• Soil degradation creates serious problems only for some smallholders.

• Off-site damage is much more costly, and forces the State to act.

• Drainage is generally improved (concrete channels} to reduce damage.

• Land husbandry seeks to act on the cause and improve infiltration by modifying production systems.

In conclusion the things we do today will affect something else at another time.  We must be aware of what our actions are capable of, especially as designers.  By learnign new development techniques hopefully we can work towards preventing situations like erosion.

-Vikki Drapeau

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