River Training Work

(The year from 1990 to 2000 has been designated the International Decade for Natural Disaster Reduction)

Problem:

An ordinary river started changing its course. During the rainy season, the nearby inhabitant areas get affected from the flood water.

Life during flood period
(Prediction and safety factor can work to some extent, but cannot eliminate the problems completely)

Purpose:

To protect the inhabitant area from the flood water and to train the river from changing its course.

Procedures:

Flood hazard areas are determined using statistical analyses of records of river flow, storm tides, and rainfall.

Disaster Preparedness Planning:

It is a cycle composed of several phases. This includes hazard analysis, vulnerability analysis, mitigation, prediction and warning, response and recovery.

A map for rescue showing the safe areas and their routes for the flooding time should be placed in public areas. This will help the public to get to the safe place during the flood period.

1. Desk study of the project area.
   This includes the study of:
• Aerial photograph of the project site
• Topographic map of the project site
• Geological map of the project site
• Hydrological data including the peak flow of the river.
2. Detailed survey of the project area including Longitudinal section, Cross section, flow pattern and the discharge of the river.
3. Estimate the peak flow for the period of 30 or 50(fewer) recurrence year from the data available.
4. Also estimate the peak flood discharge for the period of 100 (more) recurrence year.
5. Design and estimate the structures such as embankment (for the high flood discharge flow), spur (to divert the flow), skeleton (to cease the velocity of flow) launching apron and revetment (to protect from scouring bed and embankment) for the peak design discharge. Design of the embankment will be of two steps. The first step will allow flood the discharge for the (fewer) recurrence year of 30 or 50. There will be a berm in the embankment higher than the flood level for 30 or 50 (fewer) recurrence years flood discharge. The second portion of the embankment will allow discharge for 100 (more) years of recurrence period.
6. Implementation of river law

Construction Work:

Construction work of embankment, spur, launching appron will be carried out. The construction of the embankment will be in two steps. The first step will allow the flood discharge for fewer recurrence year. A berm will be left and rest portion of the embankment be carried out which will be sufficient to pass the discharge for more recurrence year (100 years). There will be turfing work in the required area. The bank can be used as the small public areas, such as, children's park, playing courts, parking area.

Embankment and Spur with crated pitching

(Embankment in multiple uses)
Rare structure (Intake for Irrigation) in the embankment for flood control

Use of computers in Disaster Reduction Works:

The use of Geographic Information Systems (GIS)and models can be valuable tools for analyzing the project area in terms of hazard vulnerability. Computers are used in weather forecasting and thus becoming usefull tools for disaster preparedness.

Role of Vegetation:

• It stops erosion in the catchment area of the river. This will reduce the silt content in flow water. So there will not be silt deposition in the bed and, thus, can carry more discharge by the river. (Silt is the main factor in changing the course of the river)
• Infiltration of the soil will increase and can hold water for longer time, so reduces the run-off at a give time.

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