(HYDROLOGY & WATER RESOURSES ENGINEERING)

Prepared by;JAYDEEP DAVE - 150113106007PRERAK KACHHIYAPATE - 150113106008KISHAN MEGHAN - 150113106009

G H PATEL COLLAGE OF ENGINEERING & TECHNOLOGY

Guide by;

Dr. KHADEEJA PRIYANProf. RATAN PANCHAL

DEPRATMENT OF CIVIL ENGINEERING

HYDROLOGIC ANALYSISDESIGN FLOOD, FLOOD

ESTIMATION,FLOOD ROUTING

DESIGN FLOOD

Design floods are hypothetical floods used for planning and floodplain management investigations. A design flood is defined by its probability of occurrence. It represents a flood which has a particular probability of occurring in any one year.

TYPES OF FLOOD DESIGN

1. Spillway design flood 2. Standard project flood (SPF) 3. Probable maximum flood (PMF)

1. Spillway design flood

• Design flood specific for designing spillway of storage structure • This term is used to donate maximum discharge that can passed in hydraulic structure without causing

damage or threat to the stability of structure

2. Standard Project Flood (SPF)

• Flood that result from combination of meteorological & hydrological factors • Extreme rare combination of factors are excluded • Used in situation where failure would cause less damage • 40% - 60% of PMF for same drainage basin

3. Probable Maximum Flood (PMF)

• Extreme flood that physically possible from severe combination, • including rare combination of meteorological & hydrological combination • Used in situation where failure of structure cause life and severe damage

FLOOD ESTIMATION

• Design of water resources structure such as Spillways, Diversion work, Bridges, Culvert etc. Often require the design at a certain location in order to estimate the size, flood and, cost of those structure.

NEED OF FLOOD ESTIMATION

• To design the water resources structure such as Dam, Spillways, Diversion works, Bridges etc.• To determine the maximum Discharge and maximum potential.• Estimate cost and size of structure.

METHODS OF FLOOD ANALYSIS

FLOOD

Rational

Unit Hydrograph

Watershed ModelsEmpirical

Flood Frequency

Analysis

1. EMPIRICAL METHOD• It should be employed only when there is a in sufficient available hydrological information for performing the

detailed and precise analysis.• The various empirical formula commonly used in INDIA are

A. DICKEN’S FORMULA

B. RYVE’S FORMULA

C. MODIFIED REGIONAL FLOOD FORMULAE

A. DICKEN’S FORMULADicken (1885) made the first attempt in India to derive a general formula for determining the maximum flood on the basis of studies conducted for determining the relation between discharge rate to drainage area.

• Q=C A(3/4)

where, Q =Peak flow rate

C,(3/4) =Regression constant

A =Area of drainage (km2)

B. RYVE’S FORMULA

Ryve’s modified Dickens’s formula to suit south Indian condition.

Q=C A 2/3

C. MODIFIED REGIONAL FLOOD FORMULAE

Kumar ET AL. (1999) developed a methodology which is modify the form of the empirical formulaQT=CT

Ab

CT = Regional Parameters QT = Flood of T year return period A = Catchment Area b = To be estimated for region using Regresion

Region Value of C1. Area within 24 km from the coast 6.75

2. Area between 24 km to 161 km from the coast 8.45

3. Limited areas near hills 10.0

2. RATIONAL FORMULA

It is the most widely used for the analysis of runoff response from small catchment.This method take into account the following hydrological characteristics or process (a) RAINFALL INTENSITY (b) RAINFALL DURATION (c) RAINFALL FREQUENCY (d) CATCHMENT AREA (e) HYDROLOGIC ABSTRACTIONS (f) RUNOFF CONCENTRATION (g) RUNOFF DIFFUSION

The requirement of the rational method is that the catchment be small,The following steps are involved in this method

A. Determine the time of concentration.B. The rainfall intensity for the desired duration and frequency from the appropriate intensity-duration-

frequency. C. Runoff coefficient depends on the condition Qp= C I A

3. FLOOD FREQUENCY ANALYSIS

• Flood frequency denotes the likelihood of flood being equaled or exceed.• The return period (Tr) of all floods (Q1,Q2,…….QN) are calculate.• The curve between Q v/s Tr is plotted.• The curve can be used to determine the return period for the corresponding magnitude of flood.

4. WATERSHED MODELS

• With the advent of high speed digital computers watershed models has been developed by many investigators.

• Some interactive software packages have been developed by national. institute of hydrology for unit hydrograph derivation and flood estimation

UHPACKI (Unit Hydrograph Applications for Flood Estimation Package) FLPACK(Flood Estimation for Large Catchments ) SRA (Software for Reservoir Analysis)

5. UNIT HYDROGRAPH APPROACH

Unit hydro graph was proposed by L.K. SHERMAN.Unit hydrograph is defined as the hydrograph of surface runoff a catchment area resulting from unit depth of rainfall excess.Unit hydrograph is a linear model of the catchment.

Assumption in unit hydrograph

1. Rainfall is of uniform intensity within its specified duration. 2. The effective rainfall is uniformly distributed throughout the area of drainage basin.

STEPS REQUIRED TO DERIEVE UNIT HYDRO GRAPH

• Select Appropriate Precipitation Event.

• Remove Base flow Contribution

• Calculate Volume of Quick-Response Runoff

• Determine Excess Precipitation Depth for the Basin

• Adjust The Quick-Response Hydrograph to Represent 1 Unit of Excess

• Determine Duration

• Final Unit Hydrograph

FLOOD ROUTING

• The flood routing is a process of determining the reservoir storage volume, out flow rates and the rise of water level in reservoir corresponding to any inflow during any peak flood discharge.

• It may be defined as a technique of determining the flood discharge and arresting the same in a reservoir for some period so that the sudden flood discharge may not create any damage in D/S area.

• It is technique used for the flood control.

• Flood routing may be divided into two basic types.

1. Reservoir Routing

2. Channel Routing

RESERVOIR ROUTING

• RELATION BETWEEN INFLOW AND OUTFLOW ( CONTINUTY EQUATION )

CHANNEL ROUTING

Channel routing the storage is a function of both outflow and inflow discharges. The total volume in storage can be considered under two categories as: 1. Prism storage, and2. Wedge storage.

Prism storage• The prism storage is formed by a volume of constant c/s along the length of reservoir. It is the

volume that would exists if uniform floe occurred at the downstream depth.

Wedge storage• The wedge storage is the volume between the top of the prism and water surface.• It is the wedge like volume formed between the actual water surface profile and the top surface

of the prism storage.

REFERENCE • Nptel• Google• Mahajan publication Dr. R.B. khasiya (book)

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