Emily Madera

Chemistry (A)
Oct 17, 2016
Channelization Argument Assignment

Source #1 :
https://dpw.lacounty.gov/lacfcd/sediment/dcon/FactSheet4WatershedEnhancement.pdf
1. 1769 Los Angeles (LA) is founded and people settle along the banks of the river
1815 The Los Angeles River (LA River) floods and washes away the original Pueblo de Los
ngeles
1825 A flash flood creates swamps and diverts the course of the free-flowing river southerly into its
current location near Long Beach
1915 The Los Angeles County Flood Control District (LACFCD) is formed
1917 Taxpayers approve bond issues to build initial dams but not for substantial infrastructure
downstream of the dams
1920 Devils Gate Dam is the first dam constructed by the LACFCD
1936 The Flood Control Act of 1936 is passed, and authorizes the U.S. Army Corps of Engineers to
construct dams, channels, and other flood control measures in LA County
1938 The Flood of 1938 heavily affects public opinion on the safety of rivers. Federal assistance is
requested and the U.S. Army Corps of Engineers takes the lead role in channelizing the river 1960
The LA River channelization project is completed to form a 51-mile engineered waterway
2. The first dam built by the Los Angeles County Flood Control District, was a direct response
to catastrophic flooding within the Los Angeles River floodplain. Due to the construction of
dams and the flood risk management they provide, today, many Los Angeles neighborhoods
are built in floodplains.
3. Los Angeles rivers have been straightened, widened, deepened, and relocated to help
prevent flooding and to keep the rivers from changing course and flowing through Los
Angeles neighborhoods and business districts. Some channelized rivers have concrete lining
and little or no habitat. Sometimes, these changes make the rivers less suitable for plant and
animal habitat and less enjoyable for people.
Pro(s): A rivers path naturally shifts and bends (or meanders) over time, often moving from one
side of a valley, or floodplain, to another. Bends and curves in the river are important because they
help provide critical plant and animal habitat, trap sediment to improve water quality, and help
prevent erosion by slowing water and protecting banks from damaging high flows
Con(s):Over the last 100 years, homes and businesses have been built along Los Angeles rivers.
These rivers have been managed with dams, channelization, and other means; therefore, any efforts
to return these rivers to a more natural state need to carefully consider potential impacts to
residents and property owners. The current system helps reduce flood risk for Los Angeles
communities and helps store scarce water for later use.
Source#2:
https://www.kcet.org/departures-columns/los-angeles-flood-of-1938-cementing-the-rivers-f
uture
1. os Angeles River once defined life in the area. Before there was California, or even the
L
United States, the Gabrieleo Indians had a community of over 45 villages dotting the San
Fernando Valley and present day Glendale, and the River was their foundation, providing
water and a diverse selection of food. In 1769, Spain's Gaspar de Portola "discovered" the
river during his explorations, dubbing it El Ro de Nuestra Seora La Reina de Los ngeles
de Porcincula.
2. Between February 27th and March 3rd, 1938 Los Angeles was hit with two storm systems
delivering record breaking rainfalls. By March 3rd, the San Gabriel Mountains received 32
inches of rain, (more than their average yearly total). Los Angeles received over 10 inches of
rainfall over the 5-day storm. There were 115 people who lost their lives and thousands of
people were evacuated, over 6000 homes were damaged or destroyed. 108,000 acres (one
third of Los Angeles) was flooded.
3. The river would typically be dry for the most part of the year, winter rains would bring
them dramatic and unpredictable flash floods in the 1930s. After a devastating flood in
1938, Angelenos began to demand flood control measures, resulting in the Army Corps of
Engineers' work over the next 30 years to essentially turn the river into a man-made storm
drain.
4. Channelization of the river began a few months after the disaster in earlier 1938. With
funding, contractors and construction crews began their process of lowering and widening
the channel and cementing the banks and river bottom. 20 years later, contractors moved
"twenty million cubic yards of earth (roughly 800,000 dump truck loads worth). They
mixed 3.5 million barrels of cement, placed 147 million pounds of reinforced steel, and set
460,000 tons of stones.," according to Blake Grumpecht's "The Los Angeles River, Its Life,
Death and Possible Rebirth." 278 miles of river and tributaries were retrofitted and more
than 300 bridges were built.
5. With the river encased in cement, the natural sharp turns were now straightened. As in all
naturality of the Earth had been shaped into the way that humans thought was best. (what a
shocker) Any evidence of vegetation was completely removed, allowing runoff from the San
Gabriel Mountains to escape through the river and out of Long Beach at up to 45
miles-per-hour. Streets and sewers were connected to drains along the river, designed to
quickly capture and move rainfall away from the surrounding streets.
Pro(s): Channelization of the Los Angeles River was a good move because it did prepare the city
for any heavy rain weather in the future. It also prevented the city from flooding like what
happened in 1938. It also modified the city in a way that it would become helpful for the new
generations to come.
Con(s): The cons of channelization in the Los Angeles River was that channelization should have
been a step more towards the future, because by adding the channel made people feel safer in L.A
and encouraged the city to then become overpopulated over the years.
Source #3 :
http://www.thisland.illinois.edu/60ways/60ways_25.html
1. From the 1920s through the 60s, it wasn't unusual for landowners to channelize, or
straighten, the streams meandering through their land.
2. By straightening the kinks in a stream, landowners increased the speed of water moving
downstream and the rate at which water drained away from their land. Straightening the
channel also made their fields more farmable because now they could farm along a straight
waterway. But as many discovered, channelization often makes things worse in the long
run.
3. By increasing the velocity of water moving in the channel, the flowing water scours the
stream bed and deepens the channel. This means the banks are higher and often more
unstable. Huge chunks of the bank can suddenly crumble into the stream. As channelization
increases streambank erosion, more sediment enters and clogs the stream, while the
accelerated velocity of water increases flooding downstream.
Pro(s): In providing an alternative water supply to your animals, use a pressure tank in the
system because it reduces the cycling of the pump. Rapid, repeated cycling reduces the life of the
pump motor and pumping efficiency.
Vegetative filter strips are strips of grass, trees, and/or shrubs planted between water and
cropland. They provide four basic forms of protection.While vegetative filter strips provide
protection along waterways, a critical area planting is used to protect small, isolated areas
in a field that are being damaged by erosion.
A farm pond can be both scenic and practical. A pond can capture runoff water, and it can
provide water for livestock, household use, irrigation, fire fighting, and orchard spraying. It
can also offer fishing, swimming, picnicking, ice skating, and wildlife habitat. You can
create a farm pond by building a dam across an existing gully or low-lying area. The ideal
topography is a wide, gently sloping basin with rather steep banks that come closely
together at the dam site.
Con(s): Channelization reduces the amount of vegetation along the streambank, which means less
food and cover for wildlife. Increased sedimentation makes it difficult for some fish to feed and
spawn, and the increased velocity of the stream drives out fish that cannot tolerate fast-moving
water.
Streambank erosion is an inevitable process, but by letting the stream meander naturally, at
least the process will be a slow one. With channelization, it can take only 10 years for
streambank erosion to do the amount of damage it might have taken 100 years to do
naturally.
By cutting off the access of livestock to streams and ponds with fencing, you reduce your
animals' contact with waterborne bacteria that can cause bovine leptospirosis, mastitis, and
other ailments.
The buffer zone of vegetation growing between the fence and stream provides
erosion-control, as does keeping livestock away from the streambank.
In Ohio, researchers found that fencing cattle away from a stream cut soil erosion by 40
percent and reduced the amount of sediment reaching the stream by 50 percent.
Source #4 :
https://www.kcet.org/shows/departures/channelization-of-the-arroyo-
seco
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Source #5 :
https://www.kcet.org/shows/lost-la/the-santa-ana-river-how-it-shaped-orange-
county
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Source #6 :
http://folar.org/river-environment/
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