Flood Mitigation

By Eng. John Celeste

Introduction:

To mitigate flood in our country especially in our Province Pangasinan and our City of Dagupan, we have to know the causes of flood, types of flood and effects of flood in the community.

Flood mitigation is a concerted effort to reduce and prevent damages caused by floods to people, property, environmental, commercial   residential and agricultural areas.

Celeste

Failure to mitigate flood may result to loss of life, properties and income. If not given utmost attention, it may affect the residential, commercial and agricultural lands destroying homes, business establishments and agricultural production including fishponds and salt farms.

It is not worthy to mention that our country is importing tons of rice and salt and other agricultural products due to tremendous flooding.

Knowing the types and causes of flood will help concerned agencies to properly plan and design the desired intervention in terms of green flood control projects and grey flood control projects considering availability of fund from the government.

Types of Flooding

1.    Flash Flooding-- heavy rainfall, denudated forest, destroyed retention pond at watershed area.

2.    Urban Flooding—poor drainage system, reckless garbage disposal, stagnant water, river siltation, bottleneck, congestion, overflow,

3.    Coastal Storm Surge- strong typhoon, tide

4.    Dam flooding—poor O&M

5.    Groundwater Flooding—water table rises, swamp

Causes of Flood

NATURAL ENVIRONMENT

1.    Storm, heavy rain

2.    Landslides, erosion

3.    Sedimentation/Siltation

4.    Climate Change

MAN-MADE ENVIRONMENT

1.    Improper land use/denudation of watershed area

2.    Improper disposal of garbage, waste and debris in the river.

3.    Illegal Structures inside the river and its easement area

4.    Improper planned, designed and constructed flood control structures

5.    Lack of appreciation/caring of the rivers and creeks that were created by God.

6.    Filling up of creeks/waterways with earth materials.

7.    Poor Operation and Maintenance of Drainage System

8.    Stagnant water— water pollution, water borne diseases

General Solutions

1.    Strict implementation of land use, replanting, reforestation

2.    Proper disposal system of garbage, waste and debris

3.    Demolition of all illegal structures inside river cross-section and easement area.

4.    Preparation of hydraulic design and structural design before construction

5.    Taking care of rivers and creeks created by God

6.    Restoration of creeks being filled up by earth materials

7.    Regular cleaning of drainage canals and maintenance of drainage outlet structures

8.    Checking of canal bed elevation and drainage outlet to river, pumping out drainage/stagnant water to river

Specific Hydraulic Solutions to Lower Flood Level in the River/Creek to Below Natural Ground (Grey Flood Control)

1.    Compute watershed/catchment area.

2.    Compute maximum flood discharge (volume of water in cubic meters per second) at certain stations of the river considering there are tributaries

3.    Assume maximum flood elevation in the river or creek to be below adjacent natural ground

4.    Compute designed width and depth of river based on maximum flood discharge and maximum flood level

5.    Align proposed river dike protection more or less in straight line or uniform designed width throughout for smooth flow of flood discharge to the sea.

6.    Resettle those affected families to provide area for river easement

7.    Demolish all illegal structures and remove illegal land reclamation along rivers and creeks.

In SUMMARY, it is a matter of widening and deepening of the river or creek to accommodate flood water to flow continuously and smoothly at right amount of flood discharge, at right time and at right place where it wants to go.

Likewise, restoring of lost waterways such as creeks can be of great help also to mitigate flood in the city, municipality or barangay.

Should there be not enough waterways to discharge the flood, the solution is to add and construct other waterways like what government is doing constructing supplementary or secondary roads.

We all know that rivers, creeks and other bodies of water are beautiful sceneries conducive to relaxation and physical exercise nearby them.

God already initiated, identified and created the waterways- rivers and creeks. If necessary, we could also add and create ones. We should take care and protect them to protect us from flood.

(Celeste, an Engineer, is a retired regional manager of the National Irrigation Administration. He is presently a member of the Dagupan Flood Mitigation Commission (DFMC))