New Page 1

SMALL HYDROELECTRIC ENERGY

WHAT IS HYDRO ELECTRICITY?

The generation of electricity through water pressure is called hydro electricity. Embankments usually are built to reserve water and create differences in water levels. Lakes in high altitudes are also used for the same purposes (the storage of potential energy within the water as the "fuel" for power generation). Five factors are used to determine the kind of dam to be built:

The height of water to be stored,
The shape and size of the valley,
The geology of the valley walls and floor,
The availability, quality and cost of construction materials, and
The availability and cost of labour and machinery.

Analyzing these factors in detail determines which dam must be chosen from either embankment dams or concrete dams. Between these two major types of dam, four different kinds of dams are available. The following table illustrates the differences between the dams.

Dam	Description	Advantages	Disadvantages
ED: Concrete Faced Rock fill Dams	Built with a large amount of sand, rock and soil with a thin layer of concrete on the upstream side to prevent water leakage. The basic construction materials are compressed to strengthen the dam.	Very low cost in both construction materials and labour. Materials are easy to find. A Constructor usually uses the rock and sand found in the surrounding area. Easy to build.	Large amount of construction materials taken from the surrounding area could lead to large environmental destruction. Does not last as long as Concrete Dams.
ED: Clay or Soil - Cored Rock fill Dams	This kind of dam is similar to the concrete faced rock fill dams as it is also consists of large amounts of sand and rock. The only difference is that this kind of dam uses clay or soil inside the structure for waterproofing.
CD: Concrete Gravity Dams	Uses the actual weight of the concrete to hold the water. There are two ways of reducing concrete in a gravity dam. One uses "high-tension steel cables anchored deep in bedrock". The other one called a Buttress Dam* uses legs or buttresses on the downstream side. These legs transfer the force to the foundation.	Cannot be washed away easily. Lasts longer than embankment dams Minimum of 8% concrete is reduced if steel cables are added to the dam, and more for the Buttress Dams method.	More expensive than Embankment Dams in terms of materials and labour costs.
CD: Concrete Arch Dams*	Unlike the concrete gravity dams, arch dams use a special arch shape (curved toward upstream) to transfer the force to the two sides of the valley and the foundation.	Strong, with the consideration of the geological foundation of the gorge. Less expensive than gravity dams by reducing 90 % of the concrete.
*Sometimes combination of Buttress Dams and Arch Dams are used when the opening is too wide with a limited budget. This kind of dam is called multiple arch dams -- Many arches are built with the support of buttresses.
*ED: Embankment Dams CD: Concrete Dams*

Power stations that contain turbines and generators are built near the downstream side of the dam. Pipes or channels are used to direct water from the storage to the stations. Within the station, water pushes the turbine that generates electricity and then exits through the tailrace.

WHAT ARE THE ADVANTAGES OF HYDRO ELECTRICITY?

The main advantage of hydro electricity is that the “fuel” is renewable and cheap. The only costs of hydro electricity are the expenses for building and maintaining the power stations and the dams. There are no costs for fuel or the transportation of such. The whole process is also environmentally friendly, as it does not create any air, chemical, water or thermal pollution. Other than the advantages mentioned above, the increase in water level could promote recreational activities such as kayaking and fishing. Furthermore, the higher level of water gives a better habitat for fish to grow and live.

WHAT ARE THE DISADVANTAGES OF HYDRO ELECTRICITY?

Although hydro electricity has many advantages, there are still quite a few setbacks. The increase of water level might provide a better habitat for fish, but it could also destroy the habitat for humans and other species' by the flooding of land. Flooding also causes soil erosion on the watershed's wall that could have harmful impact on the vegetation of the area. Along with the disruption of natural orders, flooding also threatens historical landmarks found alongside the river system. A hydro dam can also be a potential time bomb for cities located downstream.

hydro.gif (27931 bytes)