Selection of Spillways

• The Bureau of Indian Standards code IS: 10137-1982 “Guidelines for selection of spillways and energy dissipators” provide guidelines in choosing the appropriate type of spillway for the specific purpose of the project. The general considerations that provide the basic guidelines are as follows:

Safety Considerations Consistent with Economy :

• Spillway structures add substantially to the cost of a dam. In selecting a type of spillway for a dam, economy in cost should not be the only criterion.The cost of spillway must  be weighed in the light of safety required below the dam. 

Hydrological and Site Conditions :

• The type of spillway to be chosen shall depend on:

1. Inflow flood; 

2. Availability of tail channel, its capacity and flow hydraulics; 

3. Power house, tail race and other structures downstream; and 

4. Topography 

Type of Dam :

• This is one of the main factors in deciding the type of spillway. For earth and rockfill dams, chute and ogee spillways are commonly provided, whereas for an arch dam a free fall or morning glory or chute or tunnel spillway is more appropriate. Gravity dams are mostly provided with ogee spillways. 

Purpose of Dam and Operating Conditions 

• The purpose of the dam mainly determines whether the dam is to be provided with a gated spillway or a non-gated one. A diversion dam can have a fixed level crest, that is, non-gated crest.