Flood Management

Flood ControlFlood Estimation

Flood Routing

Flood Damage

Flood Damage

Classification of floods• a) Fluvial Flooding: – from rivers and streams, including that resulting from the

restricted capacity and blockage of culverts conveying watercourses;

• b) Coastal Flooding:– from high tides and/or storm surges;

• c) Pluvial Flooding: (sometimes known as ‘urban’ or surface water flooding)– resulting from the sensitivity and limiting capacity of the existing

or proposed surface water drainage network and combined drainage systems

• d) Groundwater Flooding.– man-made situations can result in unexpected and catastrophic

flooding. Indicative areas of concern include reservoirs and dams,, and the inadequate capacity of culverts, particularly below embankments.

How are flood hazard areas regulated

• Flood hazard area mapping• Limiting construction in the floodway and

flood fringe• Limiting fill in the flood way and flood fringe• Placing structures above the Base flood

elevation• Limiting reconstruction and additions with the

floodway and flood fringe

•Flood Forcasting•Flood fighting- emergency measures•Evacuation and shelter Management•Flood Insurance•Flood Zoning •Changing cropping pattern

The Snyder unit hydrograph for 100 yr-return period

Case Study Dahej

Pluvial Flood Risk Analysis

RP: 2 yrMax Depth: 0.37

mt

RP: 10yrMax Depth: 0.47

mt

RP: 100yrMax Depth: 0.62

mt

RP: 2 yrMax Depth: 0.8

mt

RP: 10yrMax Depth: 1.0

mt

RP: 100yrMax Depth: 1.3

mt

RP: 2 yrMax Depth: 0.4

mt

RP: 10yrMax Depth: 0.5

mt

RP: 100yrMax Depth: 0.6

mt

RP: 2 yrMax Depth: 5.9

mt

RP: 10yr & 100 yr Max Depth: 11.2 mt

(100 yr )

(10 yr )

•Catastrophic inland 100yr flood is most intensive in the Dahej area with the depth of 11.2mts. •Besides the pluvial flood, anthropogenic activities have modified the slope causing water logging. Water Logged

Fluvial floods

Longitudinal Section with water profile

Profile 2 at the 33975.86 Cross sectionX-Y-Z Perspective of the flood plain

Tidal & Fluvial Flood Risk Analysis

RP: AvgMax Depth: 9.26 mt

RP: 100yrMax Depth: 14.19 mt

RP: 200yrMax Depth: 14.26 mt

•Fluvial flood is calculated with cumulative effect of river and sea flow. •Fluvial flood from R.Narmada would extend into the land in the north upto 10 kms. in RP: Avg, 100 & 200yr flood.•High tide line outlines the coastal flood influence zone.

High tide area

Groundwater Flood Risk AnalysisNo Ground Water FloodingWater table is below sea level in Dahej area. Threat of sea water intrusion and subsequent salinity intrusion in the area if groundwater pumping is allowed in the area.

“Zero” water table contour shifts towards the sea in monsoon period indicating that the artificial recharge methods would work in the area.

-1

0

1

-1

0

1

Taluka Map

B1B2

B3D

C

A

Flood Mitigation- Principal concepts

Rainwater harvestingReservoirs detention: At deep valleys

Levees and floodwalls: Along Stream channel

Channel improvements: By dredging, channelisation, diversion

Crossings and roadways: Elevated roadwaysDrainage and storm sewer improvementsDrainage system maintenanceLocal Structural protection: Build-up local embankments, plant

vegetation, cracks in gullies.

Proposal for arresting the catchment at NH at Bharuch to be expedited

END