Dam

 

Hungarian Falls Dam (Dover Cr)

Earth Science, Big Idea 9 - Humans significantly alter the Earth

Today the fact that our planet’s surface is mostly ocean isn’t its dominant feature. Today, we live on a planet of humans, and we and the planet are linked. It’s a human world and humans have been and continue to change our world.

Big Ideas

Why build a dam?

Dams are built for flood control, fire and farm ponds, power generation by hydroelectricity (about 10% of US power production), irrigation diversion, fish and waterfowl habitat, water reservoirs, livestock watering, habitat improvement, recreation, mine waste retention, mine tailings and navigation.


Hydropower is a very attractive energy source because it does not pollute.  Success of hydropower dams depends on the same parameters that control the erosion of the plunge pool--the drop in elevation where kinetic energy is developed. Michigan’s potential for hydropower is limited by elevation (a pretty flat state), but here there is a potential drop of about 300 feet between the dam (920 ft) and Torch Lake (601 ft). The engineering part is to get water to fall and accelerate over as large an elevation difference as possible.


The dam, built in 1925, is an earthen embankment about 170 feet in length with 2 spillways. Water from the pond was delivered to the Ahmeek and Tamarack mills by a 14 inch pipe, for use in fire protection. Before this upper part of Hungarian Falls was acquired by the Keewenaw Land Trust in 2013, the area was owned by the Torch Lake Area Fire Protection Authority that used the reservoir as a water source to fight fires. Upgrades to municipal water supplies have replaced the pond as a water source, so the water supply line from the dam was cut.

Scale of the dam?

As the dam filled, not much water would have been allowed down the creek’s course. The pond is now about 0.6 acres with an average depth of about 6 feet and 3 million gallons of water. Before the Dam was built the valley looked much like the rest of the creek at this point, with the mainly red Jacobsville sandstone walls, some of which can still be seen at the edges of the reservoir.

What is an earthen embankment or earthen dam?

It is a dam built of soil materials (sand, loam, clay, and so on), with an almost triangular cross section. Earthen dams are commonly used in many countries because of their simplicity of construction and maintenance. Earthen dams may be built on virtually any type of ground base, with a rock fill and paving stone facing, covered with concrete or reinforced-concrete slabs which are used to protect the upstream (pressure) slopes of earthen dams against wave action. The downstream slopes are protected by planted grass, turf, poured gravel, and crushed stone.

Since we can see that the spillways are covered in concrete, it is likely that the facing of the dam is also of concrete, but the other side of the dam should only have soil and grass covering it!

The Hardy Dam on the Muskegon River, in Big Prairie TownshipNewaygo County, Michigan is also an earthen dam like the one at Hungarian Creek. It is the third largest earthen dam in the world and the largest east of the Mississippi River. Its impoundment forms a lake with over 50 miles of shoreline. The dam impounds a reservoir of 4,000 acres (1,618 ha) and it uses hydroelectricity to produce up to 30,000 kilowatts of electricity.

How do small dams like this fail?

There are 3 main types of failure that can occur:.

1.Over-topping failures – vegetation is weakening the top of the structure.

2.Seepage failures – there are large trees and bushes penetrating the dam.

3.Structural failures – there are large trees and bushes penetrating the dam.

All of the above failures are related to each other.

What should we do about the dam?

Most small dams that no longer have a specific purpose are removed. Of course this takes time and money, but the result is that the course of the stream or river is returned to its natural course. This usually helps the environment return to its original state. It also removes the possibility that an older dam will suddenly fail, which in this case would result in 3 million gallons of water suddenly pouring down the creek bed in a flash flood that would sweep all before it!

1977: The Kelly Barnes Dam, an old earthen dam in Georgia, gave way in the middle of the night. Internal erosion probably caused the failure. Thirty-nine people were killed at a small bible college below the dam.

1972: In West Virginia, a coal slurry dam, weakly constructed and with an inadequate spillway, collapsed during a period of moderately heavy rain. 125 people in Buffalo Creek Hollow below were killed.

Are there too many dams?     

By the end of the 20th century, humans had placed 50,000 dams on more than half of the earth's major rivers. The consequences of this massive engineering has been beneficial, but there is a downside, particularly in developing countries. In some cases dams have wiped out species; flooded huge areas of wetlands, forests and farmlands; and displaced tens of millions of people.


Why make so many dams?

Dams can be very, very useful. They can control flooding, produce large lakes that can be used for leisure (see Lake Mead, right), create jobs for thousands over many years (the Hoover Dam (right) is one example and one of the most useful, is to make Hydroelectric power (in this case for mighty Las Vegas!).

How does a dam make electricity?

The water in the dam falls through a tunnel to the bottom of the dam and turns a type of propeller (like in wind farms), but with more blades, called a turbine. This is connected to magnets that turn in a generator and produce electricity by induction. When there is low demand, the electricity is used to pump water at the bottom of the dam back up to the reservoir or the amount of water falling through the tunnel is reduced.

This work was supported by  National Science Foundation award #0831948.

Stats

NAME  Hungarian Falls

LOCATION  Hubbell, MI

KMZ  download HungFallsGTour.kmz

SUBJECTS Hydropower, Dam


Author:  Clive Wardell

1. The Fault     2. Dam    3. Crossbedding   4. Potholes    5. Plunge Pool   6. Bigger River?    History