floodplain management d nagesh kumar, iisc water resources planning and management: m8l5 water...
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Floodplain Management
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L5
Water Resources Systems Modeling
Objectives
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L52
To discuss flood control measures
To estimate damage caused by floods
To discuss HEC flood damage analysis package
Introduction
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L53
Floodplain: Land adjacent to the river or stream that is subjected to occasional or
periodic flooding
Acts as a conveyance or temporary storage for flood flows
Main objective of flood control is to reduce the negative consequences of floods
Flood control is normally done
By constructing structural measures such as reservoirs, diversions etc or
By nonstructural measures such as flood warning, flood proofing etc
Floodplain management comprises all engineering, nonstructural and
administrative measures to minimize the losses due to flooding
Flood Control Measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L54
Flood control measures can be broadly classified into
1. Structural and
2. Nonstructural measures.
Three functional relationships are assessed to determine the value of these
flood control alternatives
1. Stage-damage relationships which give the flood severity in terms of damage
cost at various stages;
2. Stage-discharge relationships (or rating curves) and
3. Flood frequency relationships which give the recurrence interval vs. flood
magnitude
Flood Control Measures
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L55
Functional relationships without any control measures are as shown
Flood control measures modify one or more of these relationships to reduce
the damage due to flood
Damage cost Discharge Exceedance frequency
Functional relationships for flood assessment (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Structural measures
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L56
This includes
Flood control reservoirs
Diversion structures
Levees and
Channel modifications
Structural measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L57
1. Flood control reservoirs Store flood waters and release it subsequently after the flood event Reducing the magnitude of peak discharge Frequency relationship is modified due to the decrease in the peak event
Long term use modify the stream regime and can result in channel degradation at
downstream sections, thereby changing the rating curve.
Damage cost Discharge Exceedance frequency
Effect of reservoir (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Structural measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L58
2. Diversion Structures
Divert flood flows from damage centers
Reduce the peak flows at those places
These structures also modify the frequency curve
Other two relationships are not altered.
Effect of diversion structures (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Damage cost Discharge Exceedance frequency
Structural measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L59
3. Levees Keep flood flows from flood plains damage centers Reduces the damage in protected areas from water surface stages in the main channel Modifies the stage-damage relationship by truncating it at a stage equal to the design elevation
of levee Conveyance area of the flood water is reduced due to the obstruction from levee This results in increased stages for discharges Hence, stage-discharge relationship is shifted upward This will also result in increase in downstream peak discharge, thereby shifting the frequency
curve upward
Effect of levees (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Damage cost Discharge Exceedance frequency
Structural measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L510
4. Channel Modifications Improve the conveyance characteristics by lowering the stage for a particular discharge This lowers the stage-discharge relationship Peak discharges are passed through at low stages decreasing the effect of natural valley
storage during a flood This results in high peak discharges downstream which causes an upward shift in the
frequency curve
Effect of channel modifications (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Damage cost Discharge Exceedance frequency
Nonstructural measures
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L511
These include Flood proofing, Flood warning and Land use controls
Flood proofing
Modify the damage potential of structure exposed to flood damage
This includes elevating structures, water proofing exterior walls, rearranging the
structural work space etc
It shifts the stage-damage relationship upward
Effect of channel modifications (Source: U.S. Army Corps of Engineers Hydrologic Engineering Center)
Damage cost Discharge Exceedance frequency
Nonstructural measures…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L512
Flood warning
Reduces the damage by providing prior notice to the flood plain inhabitants
The lead time provides time to do minor flood proofing, or to remove the property
susceptible to flooding.
This needs real time forecasting and communication facilities.
Land use controls
Include many administrative actions such as zoning, building ordinances, building
codes etc.
Estimation of Flood Damage
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L513
Damages from floods may be classified as:
1. Direct damage from properties
2. Indirect damage from lost services and businesses, rerouting traffic etc.
3. Secondary damages from hardships to those depend on the outputs from the
damaged properties or hindered services
4. Intangible damages like environmental quality, social well-being and aesthetic
values and
5. Uncertainty damages due to uncertainty in flooding
Most common method for flood damage assessment is through empirical depth-
damage curves
Estimation of Flood Damage…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L514
Individual or aggregated estimates of stage vs. damage curves for the crops,
structures, roads, utilities etc. in the floodplain need to be prepared through a
property suvery of the whole floodplain
Stage – damage relationship is then related with the stage – discharge relationship to
derive the damage – discharge relationship.
This is further related with the discharge – frequency relationship to derive the
damage – frequency relationship (illustrated in the next slide)
Estimation of Flood Damage…
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L515
Damage cost Discharge
Discharge Exceedance frequency
Stage – Damage Relation Stage – Discharge Relation
Damage – Discharge Relation Discharge - Frequency Relation
Exceedance frequency
Damage - Frequency Relation
Estimation of damages (Source: U.S. Army Corps of Engineers Hydrologic
Engineering Center)
HEC Flood Damage Analysis Package
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L516
Hydrologic Engineering Center Flood Damage Analysis (HEC-FDA) by U.S. Army
Corps of Engineers
A package of hydrologic, hydraulic and flood damage programs linked to data
storage system
Data storage system called HECDSS transfers data automatically between the
programs linked to it
Package contains
Three hydrologic and hydraulic programs
Five flood damage analysis programs
Three data management programs and
A library of data management software.
HEC Flood Damage Analysis Package
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L517
(i) Hydrologic analysis programs:
(a)HEC-1:
Flood hydrograph package
Simulates rainfall-runoff, simple reservoirs and hydrologic channel routing
Develops existing, without and modified flow frequency curves.
(b)HEC-2:
Water surface profiles
Computes steady-state, uniform flow profiles
Used to develop elevation-flow rating curves
(c)HEC-5:
Simulates flood control and conservation systems, complex reservoirs
Develops existing, without and modified flow frequency curves.
HEC Flood Damage Analysis Package
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L518
(ii) Flood damage analysis programs:
(a) Structural Inventory for Damage analysis, SID: Processes inventories of structures in the flood plain Develops elevation – damage relationships
(b) Structural Inventory for Damage Analysis Edit Program: Edits the structure inventory and damage function files for SID program
(c) Damage Reach State-Damage Calculation, DAMCAL : Same as SID, except develops elevation – damage relationships for a geographic
unit.
(d) Expected Annual Damage, EAD: Computes expected annual damage and compares flood damage mitigation plans
(e) FDA2PO: Computes the reference flood elevation at structure and stores stage-flow rating
curves
HEC Flood Damage Analysis Package
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L519
(iii) Data management programs
(a) Paired-function Input Program, PIP:
Inputs paired function relationship to a data storage system (DSS) data file.
(b) DSSUTL:
Performs utility functions on data stored in the HEC-DSS data file.
(c) DSPLAY:
Displays tables and plots in HEC-DSS data file.
D Nagesh Kumar, IIScWater Resources Planning and Management: M8L5
Thank You
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