Hydrology & Irrigation. Civil Engineering

Transcription

1 Hdrolog & Irrigation For Civil Engineering B wwwthegateacadeco

2 Sllabus Sllabus for Hdrolog & Irrigation Hdrolog: Hdrologic Ccle, Precipitation, Evaporation, Evapo-Transpiration, Watershed, Infiltration, Unit Hdrographs, Hdrograph nalsis, Flood Estiation and outing, eservoir Capacit, eservoir and Channel outing, Surface un-off Models, Ground Water Hdrolog - Stead State Well Hdraulics and quifers; pplication of Darc s Law Irrigation: Dut, Delta, Estiation of Evapo-Transpiration; Crop Water equireents; Design of Lined and Unlined Canals, Head Works, Gravit Das and Spillwas; Design of Weirs on Pereable Foundation; Tpes of Irrigation Sstes, Irrigation Methods; Water Logging and Drainage; Canal egulator Works, Cross-Drainage Structures, Outlets and Escapes nalsis of GTE Papers Year Percentage of Marks Overall Percentage % : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco

3 Contents Contents Chapter Page No # 1 Open Channel Flow 1 15 Introduction 1 Tpes of Channel 1 9 Pressure Distribution Hdraulic Jup #2 Irrigation Introduction Flow Irrigation ssignent 22 nswer Kes & Explanations 22 #3 Water equireents of Crops Definition Dut at Various Places Optiu Utilization of Irrigation Water #4 Soil Moisture Irrigation elationship Introduction 28 Field Capacit Solved Exaples #5 Sedient Transport and Design of Irrigation Channels Sedient Transport Mechanics of Sedient Transport Water Logging Control Tube Wells Design of Channels Kenned s egie Theor Lindle s egie Theor Design of Irrigation Channel b Lace s egie Theor Causes of Failure of Weir or Barrage on Pereable Foundation Bligh s Creep Theor for Seepage Flow Lane s Weighted Creep Theor 57 Khosla s Theor and Concept of Flow Nets Exit Gradient 67 ssignent 68 nswer Kes & Explanations 69 : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco i

4 Contents #6 Hdrolog Introduction 70 Hdrologic Ccle Water Budget Equation World Water Quantities 74 Precipitation Measureent of Precipitation Preparation of Data Frequenc of Point ainfall Evaporation Variation of ET/PET Measureent of Infiltration Stage Discharge elationships Measureent of Velocit Hdrograph and unoff Base Flow Separation S Curve Technique Floods Estiation Well Hdraulics Saturation Foration Well Hdraulics Introduction Stead Flow in Open Well ssignent nswer Kes & Explanations Module Test Test Questions nswer Kes & Explanations 131 eference Books 132 : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco ii

5 CHPTE 1 "In order to succeed ou ust fail so that ou know what not to do the next tie" nthon J D'ngelo Open Channel Flow Learning Objectives fter reading this chapter, ou will know: 1 Tpes of Channel 2 General Tpes of Flow in Open Channels 3 Geoetrical Paraeters of an Open Channel Flow 4 Pressure Distribution 5 Hdraulic Jup Introduction n open channel is a sloped liquid flow passage having solid boundaries with the top surface open to gaseous atosphere The top surface of the channel, called free surface which is the surface of contact between the flowing liquid and the overling gas, its subjected to constant pressure throughout its length and breadth In the pipe, flow occurs due to pressure gradient, but for open channel flow, it happens ostl for gravit The cross-section section for pipe flow is ostl circular but for open channel flow the cross-section can be of an geoetr Tpes of Channel 1 Open and Closed Channels: Open channels are also called uncovered channels have no cover at the top and it is copletel open to atosphere Close channel are called covered channels, have cover or roof at the top In other words the closed channel is a closed passage which does not run full, so that the liquid has free surface in contact with air ir occupies the space between the liquid surface and the top cover 2 Natural and rtificial Channels 3 Prisatic and Non-Prisatic Channels: channel having the sae flow cross-section throughout its length and having a constant botto flow is called prisatic channel 4 Exponential and Non-Exponential Channels: Depending on the tpe of cross-section of the channel, it is classified as exponential and non-exponential channels In case of an exponential channel, the cross-section area is prescribed b the equation K, where is the sectional area, is the depth of flow, k and n are the experiental constant The exaples of exponential channels are rectangular, triangular and parabolic channels For non-exponential channels, exaples are trapezoidal and circular channel : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 1

6 General Tpes of Flow in Open Channels Open Channel Flow 1 Stead and Unstead Flow If the flow characteristic of an open channel do not change with tie, then it is stead flow and if it is changing with flow, then it is unstead flow For ste low For unste low N t N t 2 Unifor and Non-Unifor Flow When the flow characteristics does not change with space, then it is unifor flow or else it is non-unifor flow N N Uni or low or non uni or low s s The non-unifor flow is further classified into two tpes (i) VF- apidl Varied Flow (ii) GVF- Graduall Varied Flow VF: It is defined as that flow in which the depth of flow changes abruptl over a sall length of a channel 3 Lainar and Turbulent Flow VD enol s nu er L D h r teristi Length h r teristi Diension For n open h nnel D is the h r uli r ius whi h is e ine P L in r Flow Tr nsition l Flow Turnulent Flow s Wette re Wette perieters 4 Subcritical, Critical and Super Critical Flow V F (Foru e No) Where V is the velo it o low g D D is the hdraulic depth T ue to gr vit rea : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 2

7 Open Channel Flow D T Froude no is the ratio of inertia force and gravit force Interti For e F Gr vit For e I F Sub critical flow/tranquil flow/ Steaing flow I F Then it is critical flow I F Super critical flow/apid flow/shooting flow Geoetrical Paraeters of an Open Channel Flow Free Liquid Surface d h Channel Botto 1 Depth of Flow (): It is the vertical distance b/w the lowest point in the channel section and the ree liqui sur e it is enote 2 Depth of Flow Section (d): It is the actual depth of the channel easured noral to the direction o low It is enote s 3 Top Width (T): It is the width of the channel at the free surface open to the atosphere it is enote T 4 Hdraulic Depth (D): T The h r uli epth or i erent se tion re (i) e t ngul r () (ii) Tri ngul r ( ) (iii) Tr pezoi l ( (iv) P r oli (v) ir ul r r sin ( sin 5 Wetted rea: () For ectangular (B) For Triangular (C) For Parabolic ) (D) For Trapezoidal ( ) (E) Circular ( sin ) ) l : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 3

8 Open Channel Flow 6 Wetted Perieter: The length of the channel boundar which coes in contact with the flowing liquid is called wetted perieter and it is denoted b P (a) ectangular (b) Circular r (c) P r oli (d) Trin gul r (e) Tr pezoi l 7 Hdraulic adius: 8 Bed Slope of Channel: The inclination of the channel bed with the horizontal is the bed slope of channel it is denoted b so for a unifor flow, since the bed slope and liquid surface slope are sae, then it is denoted b S S sin where, h is the vertical disp and this relation is valid for when is ver sall where, sin t n 9 Section Factor: Section factor for critical flow is the product of wetted area and the square root of hdraulic depth It is denoted b D ( ) T ( ) e t ngul r ( ) Tri ngul r ( ) P r oli T ( ) ( ) Tr pezoi l (e) ir ul r [( )] ( ) sin *r ( sin )+ For Discharge Equation for Unifor Flow in Open Channel 1 The Chez equation, V = S C hez s onst nt P To find out the value of c, (a) Kutter s Forul ( ) H ( ) Where n roughness o e i ient zin Forul ( ) For sooth sur e For rough sur e ( ) n M nning s Forul : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 4

9 Open Channel Flow 2 M nning s Equ tion V n S here the value of n = 01 for sooth surface = 004 for rough surface Channel of ost efficient cross-section n open channel of given slope, roughness and area if flow is said to be hdraulicall efficient or ost econoic section, when it carries the axiu discharge For hez s equ tion or given slope n roughness velocit is axiu when hdraulic radius is iniu Further for a given area hdraulic radius is axiu when wetted perieter is iniu ectangular Channel For ectangular channel Trapezoidal Channel ( ) b 1 Circular Channel D here D i b Exaple: Find the bed slope in channels of the following sections having top width 5 and unifor depth 2 Take the discharge value as 003 se n hez s onst nt s Find out for 1 ectangular channel 2 Triangular 3 Trapezoidal channel with side slope 1H:3V Q se T Solution: (i) ectangular V S P S : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 5

10 Open Channel Flow (ii) Triangular P T Q S P T P PS QS (iii) Trapezoidal (b+2 )=T b Exaple: The cross-section of a navigation channel is shown in figure deterine the discharge through the channel if the depth of flow in 12 the channel has a slope of 1 in 2000 and the hez s onst nt is Solution: I J D E F G H S V S : , info@thegateacadeco Copright reserved Web:wwwthegateacadeco 6