golden hazards

8/7/2019 Golden Hazards

http://slidepdf.com/reader/full/golden-hazards 1/3

Paul Jansen

12/9/2009

EES Thursday 8-11

Elizabeth Holley

Some Not So Golden Problems

Golden Valley has many natural hazards that can and do present a wide range of

problems for residents. From swelling clay and flooding to rock fall and landslides, certain

places in Golden are pretty dangerous to live in. This report should be used in order to

determine the feasibility of building in certain areas, and if construction is going to take place,

to determine building codes for safety. This report was prepared from information gathered

during field and lab exercises as well as from lecture and internet sources. The data is not

absolute but is as in depth as possible by the current research done on it by a freshmen student

at the Colorado School of Mines. It will encompass the four major geologic hazards found in and

around the city of Golden.

In the Golden Valley, there are five major rock types. These five are: Denver, Arapahoe,

Laramie, Fox Hills, and Pierre Formations. They are relatively laid out in bands from the east to

the west, with the Denver Formation furthest east, and the Pierre Formation furthest west. The

Denver Formation is comprised of sandstone and conglomerate rock. The Arapahoe is mostly

made up of sandstone, silt and shale interlace together. This formation creates the water

aquifer for the region, allowing for wells to be drilled. The Laramie and the Fox Hills layers are

comprised of sandstone interlaced with shale and siltstone. This layer does not allow water to

pass through it easily, so the water builds up above it creating the aquifer. The Pierre Formation

is made up of dark, gray shale which also hinders water movement. These layers along with

smaller rock outcrops are the reason for some of the hazards present.

The first hazard discussed in this report will be the flooding of Clear Creek, Tucker Gulch

and Kinney Run. This is a major issue for people who live near the creek, or in the floodplain

near them. Clear Creek has been drastically changed from 100 years ago in order to try and

control flooding. These days, the hundred year flood is about all that the people who live in this

area have to worry about. If the hundred year flood does happen though, insurance companies

will be paying out a lot of money. If the flood does happen, the gulch and run will have much

less problems than Clear Creek. Only areas 100 to 200 feet from either of these will be flooded.

Also a large area which holds a golf course and High School sports fields will be flooded, not

causing that much damage. If Clear Creek floods, many buildings will be damaged.

The floodplain extends north of Clear Creek all the way to about 8th

St. as seen on the

accompanying map. The city realized this and has built a park directly north, near the

pedestrian bridge, but this is not the extent of the floodplain. If there is a flood, along with



many houses, a library, Municipal Center, the Golden visitor center and other buildings will be

damaged or destroyed. I realize the city could not make this whole area a park, but putting a

library extremely close does not seem like a good idea. Some things that could be done to

mitigate this problem would be to channelize the river more so that it can accommodate more

water. They could also plant more plants along the banks in order to keep the banks fromeroding. This is about all that can be done to alleviate the flooding problem, and maybe make

the library watertight so save all the books.

The next hazard to be dealt with is swelling clay. This is a major problem for

homeowners in certain areas, and building owners in others. Since it is hard to keep the clay at

a constant level of saturation in Colorado, foundations and roads are continuously being ruined

by it. The major type of clay in the area is called Smectite. The layers between the clay can

expand from 7 to 37 angstroms. An angstrom may be 1E-10 meters, but this expansion can

occur between every molecular layer of clay and 1 meters of clay can expand to about 5

meters. It will not expand this whole way but it can expand enough to ruin foundations and

ripple roads. The areas in Golden that have moderate to high swelling potential are indicated

on the accompanying map. Swelling clay is extremely difficult to work around or with. When

building a structure, there are three different types the clay is found. It can be found in

horizontal, vertically sloping, or thin vertical layers. Mitigation for each is different. The

horizontal is the easiest to work around. If it is a thin layer, you can excavate it and backfill with

a sandy mixture. If it is a thick layer, you can build your house with a floating foundation to

accommodate minor shifts. You can also water your foundation to keep the clay at a constant

saturation level. If it is a vertically sloping layer or thin vertical layer, the best option is to

excavate and backfill or to zone it so that major buildings are not built on it. The Colorado

School of Mines is having an issue with this where the sororities are built. Foundation cracking

can clearly be seen in some of these buildings because of the swelling clay.

Rock fall is probably the most deadly of all of these since it is hard to predict when it will

happen. And when it does happen, the warning time for people below is pretty much

nonexistent. They will most likely find out when they get up for work and find that they have a

new garage door and their car weighs a couple extra tons. The most likely areas for rock fall are

at the bases North and South Table Mountain. The highest risk would be where the volcanic

rock has become exposed and is starting to erode. This is the highest risk because it forms cliffs

that allow rocks to pick up speed very quickly before hitting the more gently sloping parts and

rolling. If the rock is big enough, it will not have enough space to slow down until it hits the

subdivision directly below, or the water tank on North Table. I would like to recommend the

moving of the water tank from where it has been placed. If a big enough boulder hits it causing

it to rupture, the people below will not have to worry about holes in their houses, they will

have to worry about waking up in their neighbors bedroom cause their house floated across the



street to form a duplex. If a boulder is deemed to be at risk of falling, it can be anchored or

bolted in place. If smaller rocks start becoming a problem, metal netting can be draped over the

rock to slow them down. This procedure does not want to be used because then people have to

look at the netting when taking hikes or pictures. The highest risk areas for rock fall can be

seen on the map. They are represented by across hatched shading.

The final major hazard to be considered is the threat of landslides. Landslides are a high

risk hazard also because they give little to no warning before they happen. One of the only

ways to know is if there is a small shift in the hillside. Sometimes the slide shifts a little before

going completely. Geologists can analyze areas that are believed to be at risk for this and

determine how risky it actually is. The risky areas in the Golden area are where the slope is 30

degrees or greater. This would be the foothills and near both table mountains. This can be seen

in more detail on the maps included. The city of Golden should hire professionals to analyze

these areas and determine of we should be worried. If they find any areas that need to be fixed,

there are a few ways to go about it. The top or head of the landslide can be excavated in order

to reduce the load on the rest of it. Another way would be to drill into the toe and insert steel

cables. Then fill the hole with cement and apply tension to the cables. This pulls the toe

outward, stabilizing the landslide. If it is in an open area, the city can decide to induce the

landslide. They can do this by adding weight to the head, adding water to the head, or

removing material from the toe. These are the major hazards in and around Golden and how I

feel they should be dealt with by the city.

Bibliography

Holley, Elizabeth. "Hazards of Golden." C.S.M, Golden, CO. 3 Dec. . Lecture

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