GOVERNMENT ENGINEERING COLLEGE, VALSAD SUBJECT :HYDROLOGY & WATER RESOURCES ENGINEERING TOPIC : FLOOD MANAGEMENT & HYDROLOGIC ANALSIS AND DESING

BRANCH : CIVIL GROUP:7 UBMITTED TO : PROF. KULEEP PATEL SR NO. ENROLMENT NO. NAME 1 130190106047 NEHA V. RAKHOLIYA 2 130190106049 KRUPALI V. RATHOD 3 140193106006 SHIKA B. PATEL

FLOOD MANAGEMENT

INDIAN RIVERS AND FLOODS Himalayan rivers Rivers on the central high lands Rivers on the peninsula Rivers on the coasts

METHODS OF FLOOD CONTROL Method adopted to modify the flood Flood control measure for the channel phase Flood control measure for the land phase Flood control measure for the atmospheric phase 2) Methods adopted to modify the susceptibility of flood damage

Flood plain management Adoption of suitable development policies Effecting structural changes Flood proofing of areas Disaster preparedness and response planning Flood forecasting and flood warning

3) Methods adopted to reduce the loss Emergency evacuation Flood proofing Adopting suitable public measures Providing disaster relief Tax remission

FLOOD MITIGATION STRUCTURAL MITIGATION DAMS & RESERVOIRS EMBANKMENT CHANNEL IMPROVEMENT RIVER DIVERSION INTER BASIN TRANSFER ANTI EROSION WORKS

NON STRUCTURAL MITIGATION FLOOD FORECASTING & WARNING OD PLAIN ZONING FLOOD FIGHTING FLOOD PROOFING FLOOD INSURANCE RELIEF & REHABIITATION

FLOOD PLAIN ZONING WATER SUPPLY III III II I II I FACTORY HOSPITAL GOVT. OFFICE POWER HOUSE PARK RESIDENTIAL AREA UNIVERSITY FREQUENT FLOOD FLOOD ONCE IN 25 YEARS NORMAL CHANNEL FLOOD ONCE IN 100 YEARS

FLOOD FORECASTING BEGINNING STARTED BY CENTRAL WATER COMMISSION INDIA FLOOD FORECASTING BEGINNING STARTED BY CENTRAL WATER COMMISSION YEAR 1958 RIVER YAMUNA FORECASTING STATION DELHI RAILWAY BRIDGE

FLOOD PLAIN ZONING WARNING RESTRICTIVE PROHIBITIVE RESTRICTIVE WARNING II III II I RIVER CHANNEL

FLOOD FORECASTING AND WARNING STEPS DATA COLLECTION DATA TRANSMISSION DATA ANALYSIS & FORECAST FORMULATION DISSEMINATION OF FORECAST

FLOOD FORECASTING DATA COLLECTION HYDROLOGICAL RIVER WATER LEVEL RIVER DISCHARGE HYDROMETEOROLGICAL RAINFALL OTHER RECIPITATION eg. SNOW, HAIL ETC.

FLOOD FORECASTING AND WARNING PRESENT SYSTEM - SCHEMATIC DIAGRAM RIVER STAGE & DISCHARGE AT BASE STATION RIVER STAGE & DISCHARGE AT FORECASTING STATIONS WEATHER FORECASTS RAINFALL REGIONAL OFFICES OF I.M.D. REGIONAL OFFICES OF I.M.D. F.M.O OF I.M.D F.M. O. OF I.M.D FLOOD FORECASTING CENTRES & CONTROL ROOMS FORMULATION OF FORECAST C.E., S.E. CWC HQ MINISTRY OF WR CIVIL AUTHORITIES PRESS RADIO STATE GOVT. CONTROL ROOM ENGG. AUTHORITIES P & T DOORDARSHAN DEFENCE INDUSTRIES POLICE FLOOD COMMITTEE RAILWAYS

FLOOD MANAGEMENT FUTURE STRATEGIES Focused Approach Basin Wise Action Plan Flood Plain Zoning Role of Central Government Funding of Planned Flood Management Works Adequacy of Flood Cushion in Reservoirs

FLOOD DAMAGE ANALYSIS Damage to crop Damage to houses Damage to human lives Damage to live stock Damage to public utilities, roads , rails etc. Cost of relief measures.

SELECTION OF DESIGN FLOOD Design flood may be one of the following types of floods, depending the importance of the project and degree of protection required. Maximum Probable flood (MPF) Standard project flood (SPF) A flood corresponding to a desired frequency of its occurrence

A Flood accepted for the design of a structure is based on the following . Importance of the structure Economy of the structure Probable effect at its downstream Life expectancy of the structure Inconvenience but no property damage or loss of life Population density of the downstream area Economic condition of the people of the affected area Submergence of mineral, industrial and other strategic areas

DESIGN FLOOD: The design flood is the flood adopted for the design of a flood control project. It may be either the maximum probable flood or the standard project flood or flood corresponding to some desired frequency occurrence depending upon the degree of protection that should be provided by the flood control project.

MAXIMUM PROBABLE FLOOD: The maximum probable flood is the flood that may be expected from the most severe combination of critical meteorological and hydrologic condition that are reasonably possible in the region. It is estimated from the maximum probable storm applying the unit hydrograph principle. The maximum probable storm is an estimate of the physical upper limit to storm rainfall over the basin.

STANDARD PROJECT FLOOD: The standard project flood is the flood that may be expected from the most severe combination of Metrologic condition that are reasonably possible in the region. It is computed from the standard project storm rainfall applying the unit hydrograph . The standard storm rainfall may be taken as the largest storm rainfall which has occurred in the of basin during the period of weather record.

METHOD OF ESTIMATION OF MAXIMUM FLOOD The following method are commonly used for the estimation of the maximum flood in the river. Past flood mark method Empirical method Envelop cures method Concentration time method Rational method Unit hydrograph method Flood frequency method

Hydrologic Analysis and Design

Selection of design flood Before adopting any flood control measures, it is necessary to know the maximum flood likely to occur and to select a suitable design for a flood control project . The design flood may be one of the following types of flood, depending upon the important of the project and the degree of protection required, 1)Maximum probable flood 2)Standard project flood(SPF) 3)A flood corresponding to a desire frequency of it’s occurrence.

Design Flood The design flood is the flood adopted for a flood control project. It may be either the maximum probable flood or the standard project flood or flood corresponding to some desired frequency occurrence depending upon the degree of protection that should be provided by the flood control project .

Maximum probable flood The maximum probable flood is the flood that may be expected from the most sever combination of critical Metrologic and hydrologic condition that are reasonably possible in the region. It is estimated from the maximum probable storm applying the unit hydrograph principle. The maximum probable storm is an estimate of the physical upper limit to storm rain fall over the basin.

Standard project flood The standard project flood that may be expected from the most sever combination of Metrologic and hydrologic condition that are reasonably possible in the region. It is computed from the standard project storm rain fall applying the unit hydrograph principle. The standard project storm rain fall may be taken as the largest storm rainfall which has occur in the region of basin during the period of weather record.

Methods of Estimation of maximum flood Past flood marks method Empirical method Envelope curves method Concentration time method Rational method Unit hydrograph method Flood frequency method

Past flood method V = Velocity Q = Discharge R = Hydrologic mean depth N= Manning’s coefficient

Past flood marks method The maximum flood that occurred in the past can be estimated from the flood marks left by the flood. These marks are generally in the form of floating debris sticking to the banks or to the walls of the structures at the river bank. The following procedure is used to estimate the flood discharge. 1. The flood marks left along the reach of the river are connected by levelling to determine the water surface levels. The slope of the water surface is calculated from the difference of high flood levels over a known distance

2) The profile of the river is plotted and the cross- sectional area of the river is computed upto the high flood level mark. The value of hydraulic mean depth(R) is then computed. 3) After assuming a suitable value of manning’s coefficient (N) the discharge is computed from the slope area method. The velocity (V) is given by And discharge, A=is the cross section area R= the hydraulic means depth S=the water surface slope

4) For estimation of the future peak floods, the computed discharge is increased by a suitable percentage. The percentage increase is usually decided considering the period elapsed after the observed maximum flood. If this method period is long, the percentage increase is relatively small. The method is not reliable. It should be used only when other methods cannot be used.

Dicken's formula : Empirical methods The formula was developed for the north and central India. Q = Maximum flood discharge A = Area of the catchment C = Dicken’s coefficient

2)RYVE’S FORMULA: The formula was developed for the Tamil Nadu region. It is also used for catchments in south India in Karnataka and Andhra Parades. Where c= Ryve’s coefficient. Q is discharge and A is the area of catchments

3) INGLIS FORMULA: Inglis formula was developed for the catchments in Maharashtra. Where A is the area of catchment

4.Ali Nawaz Jung Bahadur’s Formula: The Formula was derived for the catchments in former Hyderabad state(A.P) Q=c(0.386 A)an n=0.925-1/14 log(0.386A) Where A is the catchment area(km2),and c is a coefficient the value of which generally varies from 48 to 60.The maximum observed value of C is 85.

5.Meyer’s formula: The formula was developed for the catchment in U.S.A Where P is a coefficient which depends on the frequency of floods with a maximum value of unity , and A is the area of catchment

6.Fuller’s Formula: The formula was also developed for the catchments in U.S.A. where Q is the maximum 24-hr flood with a return period of Tr years, and Q is the average of 24-hr flood=C A0.8,where C is a coefficient whose value varies between 0.18 and 1.88, and A is the area of catchment (km2).

Envelope Curve methods: For plotting envelops curves, the maximum flood discharges for the catchments having similar topographical features and climatic conditions are determined. The maximum flood discharge is plotted against the area of catchment. A curve is the drawn to envelop the highest plotted scattered points. If a log- log paper is used, the envelope curve can be used to determine the maximum flood discharge in future for different catchment areas.

Kanwar sain and Karpov developed two envelope curves, one for the northern and central India rivers and the other for he southern India rivers. If available data for a catchment are meager, the envelope curves developed for that region can be used for rough estimation of the maximum flood discharge.

The method is better than the empirical formula method because the selection of the coefficients on the basis of judgment is avoided. However, these curves have the same limitation as those of empirical formulae , viz.., these consider only the area of the catchment., rainfall characteristics, geology. Etc. moreover, these curves consider only the flood recorded in the past. There is a possibility that a still higher flood may occur in future. The curves developed by kanawar sain and Karpov have been used as a guidance for determining the maximum flood discharge for various projects in India. Baird and Meillnraith studied the maximum recorded flood throughout the world and gave the following formula for the envelop. A is the area of catchment

Concentration time method The concentration time is the time taken by water to flow from the farthest point of the catchment to reach the outlet. The discharge at the outlet is a maximum when the duration of the storm is equal to or greater than the concentration time. The concentration time depends upon the length of the basin and the average slope. It is usually estimated by kirpich formula

Tc = concentration time (minutes) L = Maximum length of travel (m) S = Slope of the catchment The period of the maximum effective (net) rainfall record of the catchment , and maximum discharge is calculated as Q = Maximum discharge I = maximum intensity of rainfall

Rotional methods According the rational formula, the maximum discharge is give by C= coefficient which depend upon the characteristics of the catchment. A= area of catchment. If the intensity – duration frequency curves are not available, the value of ic can be computed from the equation

The rational formula is commonly used for the determination of the maximum discharge from the urban paved area with gutters and sewers. The design of the urban drainage system is generally based on the rational formula. The formula is some times used for other type of catchments. It my be mentioned that the word rational is actually a misnomer because the method involves the determination of ic and c in a subjective, empirical manner.

Unit hydrograph method The unit hydrograph technique can be used to predict the peak flood hydrograph if the rainfall producing the flood, infiltration characteristics of the catchment and the appropriate unit hydrograph are available. The hydrograph of extreme floods and stages corresponding to flood peaks provide valuable data for purpose of hydrologic design. For design purposes, extreme rainfall situations are used to obtain the design storm, viz the hyetograph of the rainfall excess 4 causing extreme floods.

The known unit hydrograph of the catchment is then operated upon the design storm to generate the desired flood hydrograph. Design flood is the flood adopted for the design of a structure. In the design of a hydraulic structure it is not practical from economic point of view to provide for the safety of the structure at the maximum possible flood in the catchment. The type, importance of the structure and economic development of the surrounding area and associated damages in case of failure dictate the design criteria for choosing the flood magnitude of a certain return period. Standard project flood (SPF) is the flood that would result from a severe combination of meteorological and hydrological factors that are reasonably applicable to the region. Extreme rare combinations of factors are excluded. While probable maximum flood (PMF) is the extreme flood that is physically possible in a region as a result of severe most combinations, including rare combinations of meteorological and hydrological factors.

Flood frequency method Hydrological processes such as floods are exceedingly complex natural events. They are resultants of a number of component parameters (e.g. floods depend upon the characteristics of the catchment, rainfall and antecedent conditions, each one of these factors in turn depend upon a host constituent parameters) are therefore very difficult to model analytically. An alternate approach to the prediction of flood flows (and other hydrologic processes) is the statistical method of frequency analysis. The values of the annual maximum flood from a given catchment area for large number of successive years constitute a hydrologic data series called the annual series.

Annual flood series: In the annual flood series, only the highest flood of the each year is taken for analysis; whereas in the partial duration series all flood peaks above a selected peak are collected irrespective of the year in which they occur.

Partial duration series : The partial duration series has an advantage over the annual flood series because all floods above a particular peak are consider, whereas in the annual flood series, some large floods, which may be even large than the largest floods in other years, are not considered. Methods for the estimation the design flood Probability plotting method Gumbel’s method Log pearson type -3 method

1) Probability plotting method In the probability methods, the recurrence intervals are first computed for the various flood peaks. A plot is then made between the flood discharge as ordinate and the recurrence interval as abscissa. (i) Recurrence interval: Recurrence interval is the average time interval that elapses between the two events that equal or exceed a particular level. In other words, it is the average interval in which a specified event is equal or exceeded. For example, if 25 cm rainfall is 24hours on an average is equal or exceeded once in 20 years, the recurrence interval of 25cm rainfall is 20 year.

(ii) Probability of occurrence(p): the probability of an event being equal or exceeded in any one year is the probability of its occurrence. Obviously, probability is the inverse of the recurrence interval. (iii) Frequency(f): the probability of occurrence of an event express as a percentage is known as frequency. (iv) Probability of non-occurrence (q): The probability of non-occurrence of an event in any one year is given by: q= 1-p

v) Probability of occurrence at least once (R): The probability of occurrence at least once in n successive year is given by: R = 1-qn = 1- (1-p) n (vi) Probability of non- occurrence in a successive year(k): the probability that an event will not occure in any of n successive year is given by: k = (1-p) n

2) Gumbel’s distribution method Gumbel’s distribution is perhaps the most widely used distribution for the estimation of flood of various recurrence interval. Gumbel considered annual flood series. Where X= any variable like discharge = mean of variable = standard deviation of the variate K = a constant

Or In actual practice, it is the value of for a given probability (P) that is required.

or

Or Where K= known as frequency factor N is smaller and is of finite value the equation of K is modified as: = reduced mean , depending on N = reduced standard deviation, depending on N

3) Log- pearson type- 3 Distribution method In this method , the variate (i.e. Q in this case) is the first transform into logarithmic form before analyzing the data. If Q is the variate of a random hydrologic series, then another series of y variate is thus obtained such that y=log10Q. The values of the variate yT for any recurrence interval Tr is given by

K=The frequency factor which depends upon the recurrence interval and the coefficient and the coefficient of skew (g). The value of g is given by = mean of y-value n = sample size = standard deviation of y.

Example:1 For a river, the estimated flood peak for two return period by the use of Gumbel’s method are as follows. What flood discharge in this river will have a return period of 100 year? Solution: Using the Gumbel’s equation Return period(year) Peak flood 100 435 50 395

Subtracting (ii) from (i), we get

Substituting in eq.(iii), we get

Also for give T=1000 year, we have Also from the basic equation, for 1000 year and 100 year , we have

example: 2 On the basin of isopluvial map, the 50 year 24 hr rainfall of magnitude equal to or greater then 16cm occurring at Ahmedabad (a) at least once in 10 successive year, (b)two times in 10 successive and (c) once in 10 successive year. Solution: Frequency of rain fall

P= exceedance probability (a) probability of equalling or exceeding at least once in a successive year. n= 100 year

(b) probability of occurrence twice in n year (p=1-q) (q= probability of non-occurrence)

(c) probability of exceedance once in n year

FLOOD ROUTING The flood hydrograph is in fact a wave. The stage and discharge hydrographs represent the passage of waves of stream depth and discharge respectively. As this wave moves down, the shape of the wave gets modified due to channel storage, resistance, lateral addition or withdrawal of flows etc. When a flood wave passes through a reservoir its peak is attenuated and the time base is enlarged due to effect of storage.

The reduction in the peak of the outflow hydrograph due to storage effects is called attenuation. Further the peak of outflow occurs after the peak of the inflow; the time difference between the peaks of inflow and outflow hydrographs is known as lag. Modification in the hydrograph is studied through flood routing. Flood routing is the technique of determining the flood hydrograph at a section of a river by utilizing the data of flood flow at one or more upstream sections.

Hydrologic routing methods employ essentially the equation of continuity, on the other hand hydraulic methods use continuity equation along with the equation of motion of unsteady flow (St. Venant equations) hence better than hydrologic methods.

Equation for hydrologic routing The passage of a flood hydrograph through a reservoir or a channel reach is a gradually varied unsteady flow. If we consider some hydrologic system with input I(t), output O(t), and storage S(t), then the equation of continuity in hydrologic routing methods is the following: I −O = If the inflow hydrograph, I(t) is known, this equation cannot be solved directly to obtain the outflow hydrograph, O(t), because both O and S are unknown.

Reservoir Routing The effect of reservoir storage is to redistribute the hydrograph by shifting the centroid of the inflow hydrograph to the position of that of the outflow hydrograph in time. When a reservoir has a horizontal water surface elevation, the storage function is a function of its water surface elevation or depth in the pool . The outflow is also a function of the water surface elevation, or head on the outlet works.

As the horizontal water surface is assumed in the reservoir, the reservoir storage routing is known as Level Pool Routing. The outflow from a reservoir (over a spillway) is a function of the reservoir elevation only. The storage in the reservoir is also a function of the reservoir elevation. Further due to passage of the flood wave through the reservoir the water level in the reservoir changes with time h = h(t) and hence the storage and discharge change with time. It is required to find the variations of S, h, and O with time for given inflow with time. In a small time interval t the difference between the total inflow and outflow in a reach is equal to the change in storage

I t −O t = S6 where I = average inflow in time t, O = average outflow in time t. If suffixes 1 and 2 denote the beginning and end of the time interval t then the above equation becomes

METHODS OF RESERVOIR ROUTING Trial and error method I.S.D. curve method Modified pul’s method Goodrich method

TRIAL AND ERROR METHOD Trial and error method is widely adopted with the assistance of computers to reduce the time taken in long calculations involved in this method.

Inflow flood hydrograph Elevation storage curve For carrying out computations by the trail and error method , the following three curve are required. Inflow flood hydrograph Elevation storage curve Elevation outflow curve

Inflow flood hydrograph: The inflow hydrograph is the maximum flood hydrograph at the reservoir site. It is obtained from hydrograph investigation as shown in fig.

II. Elevation storage curve : The elevation storage curve gives the reservoir at different elevations. It is found from the topographical map of the reservoir as shown in fig.

III. Elevation outflow curve: This curve give the outflow rates for different elevation. The outflow from a reservoir depends upon the type of spillway and on the number of gates of the spillway as shown in fig.

I.S.D. Curve method(Graphical method) The inflow storage discharge curve method, also known as puls method. In this method following two graphs are to b prepared from the elevation storage curve and the elevation outflow curve

(2S/Δt + O) versus outflow curve Where, S = Surcharge storage O =Outflow rate Δt = Time interval

For preparing of these curves values of S and O for different elevation are obtained The value of (2S/Δt + O) and (2S/Δt - O) are then computed for different elevation. The two graphs are then plotted on same paper. The ordinates represent the outflow rate & the abscissa represent the both (2S/ 2S/Δt + O) and the flood routing eqn.(c) is a slight modification form as follows : (I₁+I₂) =(2S₁/Δt - O₁) = (2S₂/Δt+O₂)

Modified puls’ method: There are a variety of methods available for routing of floods through a reservoir. All of them use the above equation but in various rearranged manners. In Pul’s Method the equation is rearranged as

At the starting of flood routing, all the terms on the left hand side are known and hence right hand side at the end of the time step t. Since S = f(h) and O = f(h), the RHS is a function f elevation h for a chosen time interval t. Graphs can be prepared for h vs O, h vs S and h vs (S + Ot / 2), which enable one to determine the reservoir elevation and hence the outflow discharge at the end of the time step.

Goodrich method: The procedure is repeated to cover the full inflow hydrograph. In Goodrich’s method the rearranged equation is

For known S = f(h) and O = f(h), graphs are prepared for h vs O, and h vs S. Since S = f(h) and O = f(h), the RHS (2S / t +O) is a function of elevation h hence a function of outflow O as well 7 for a chosen time interval t. Another graph may be prepared for O vs (2S / t +O) . In routing the flow through time interval t, all terms on the LHS and hence RHS are known, and so the alue of outflow O for (2S / t +O) can be read from the graph. To set up the data required for the next time interval, the value of (2S / t −O) is calculated by(2S / t +O)− 2O. The computations are then repeated for subsequent routing periods.

Channel routing: In very long channels the entire flood wave also travels a considerable distance resulting in a time redistribution and time of translation as well. Thus, in a river, the redistribution due to storage effects modifies the shape, while the translation changes its position in time. In the reservoir the storage was a unique function of the outflow discharge S = f(O). However in channel the storage is a function of both outflow and inflow discharges and hence a different routing method is needed. The water surface in a channel reach is not only parallel to the channel bottom but also varies with time. The total volume in storage for a channel reach having a flood wave can be considered as prism storage + wedge storage. Prism storage is the volume that would exist if uniform flow occurred at the downstream depth i.e. the volume formed by an imaginary plane parallel to the channel bottom drawn at the outflow section water surface. Wedge storage is the wedge like volume formed between the actual water surface profile and thetop surface of the prism storage.

The flow in river during a flood belongs to the category of gradually varied unsteady flow. He water surface in a channel not only unparallel to the channel bed, but also varies with time. When such a river flow is considered, the storage between two section, will consists of two parts Prism storage Wedge storage

Prism storage: It is volume that would exist, if a uniform flow occurs at the downstream depth, i.e., the volume formed by an imaginary plane parallel to the channel bed, drawn upstream from the outflow section to the inflow section.

Wedge storage: It is the wedge like volume formed between the actual water surface profile and the top surface of the prism storage. At a fixed depth at a downstream section of a river reach the prism storage is constant while the wedge storage changes from a positive value at an advancing flood to a negative value during a receding flood.

Assuming that the cross sectional area of the flood flow section is directly proportional to the discharge at the section, the volume of prism storage is equal to KO where K is a proportionality coefficient, and the volume of the wedge storage is equal to KX(I - O), where X is a weighing factor having the range 0 < X < 0.5. The total storage is therefore the sum of two components.

K= a coefficient parameter m = a constant exponent ; whose value is found to vary from 0.6 for rectangular channels to about 1.0 for natural rivers. I = inflow, Q = outflow

Muskingum Equation: When m is taken 1.0 as found for natural rivers, the equation reduces to a liner relationship for S in term of I and O, as X= a dimensionless weighting factor between inflow and outflow, called weightage constant.

which is known as Muskingum storage equation representing a linear model for routing flow in streams. The value of X depends on the shape of the modeled wedge storage. It is zero for reservoir type storage (zero wedge storage or level pool case S = KO) and 0.5 for a full wedge. In natural streams mean value of X is near 0.2. The parameter K is the time of travel of the flood wave through the channel reaches also known as storage time constant and has the dimensions of time.