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- 1. NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />1<br />
- 2. Engineering Hydrology(CE- 235)<br />CHAPTER - I<br />2<br />INTRODUCTION<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGY<br /> Hydrology is the science of the waters of the earth and atmosphere.<br /> It deals with <br /><ul><li>Occurrence
- 3. Circulation
- 4. Distribution and
- 5. Movements of these waters over the globe</li></ul>3<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>ENGINEERING HYDROLOGY<br /> Engineering Hydrology deals with:-<br /><ul><li>Estimation and analysis of water resources
- 6. The study of processes such as precipitation, runoff, evapotranspiration
- 7. The study of hydrologic problems such as floods and droughts, and strategies to combat them</li></ul>4<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Importance of Hydrology in Civil Engineering<br />It has an important role in design and operation of water resources engineering projects like<br />Irrigation<br />Flood control<br />Water supply schemes<br />Hydropower projects<br />Navigation <br />5<br />Engineering Hydrology(CE- 235)<br />These Civil Engineering projects may fail due to improper Assessment of Hydrologic Aspect<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>6<br />Engineering Hydrology(CE- 235)<br />Vs<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>SCOPE<br />Essential for analysis, design and operation of any hydraulic structure which retains or conveys water (from the simplest culvert to the largest complex of dams, hydroelectric works, barrages and irrigation structures)<br />Designer needs magnitude of stream flow and their probability of occurrence not only for design of hydraulic structures but also for flood control<br />Combating the menace of water-logging and salinity in irrigated areas<br />7<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>SCOPE<br />Predicting relationship between characteristics of a basin and rate of flow<br />Probability of occurrence of floods and droughts<br />Water availability into the reservoir from the basin<br />Effect of rainfall occurring in basin on the magnitude of flow in streams and predict rainfall-runoff relationship of the basin and probability of its occurrence<br />8<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>SCOPE<br />Probable flood flow over a spillway, at a highway culvert or in urban storm drainage system<br />Reservoir capacity sizing required to assure adequate water for irrigation, hydropower or municipal water supply during droughts<br />Effect of reservoir, levees and other control works on flood flows in stream<br />Assessment of reasonable boundaries of floodplain<br />9<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>MAJOR ASPECTS OF HYDROLOGY<br />The main jobs of a hydrologist are<br />Collection of data<br />Analysis of data<br />prediction<br />10<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>COLLECTION OF DATA<br /><ul><li>Rainfall Data
- 8. Snowfall and Snowmelt Data
- 9. Runoff Data (Catchment Runoff and Stream Flows)
- 10. Topographic Maps, Satellite Imageries, and
- 11. Groundwater Data</li></ul>11<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>ANALYSIS OF DATA<br />Analysis of hydrologic data includes<br />Checking the data for<br />Consistency and<br />Homogeneity <br />Finding of various statistical parameters<br />12<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PREDICTION<br />Based upon the analysis followings can be predicted<br />Design values <br />Maximum possible flood<br />Maximum outflows from catchments<br />13<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>DISTRIBUTION OF EARTH’S WATER<br />14<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGIC CYCLE<br />The earth’s water circulatory system is known as Hydrologic Cycle<br />Total water supply of earth is in constant circulation from earth to atmosphere, and back to earth<br />15<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>16<br />Engineering Hydrology(CE- 235)<br />Atmospheric phase<br />Land phase<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>17<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>18<br />Evaporation<br />Evaporation<br />Interflow<br />Runoff = Streamflow<br />Volcanic outgassing<br />Infiltration<br />drainage<br />Gravity <br />Groundwater flow <br />and Baseflow<br />Subsea outflow<br />Subduction<br />Seafloor<br />vents<br />Vapor<br />Flow<br />Liquid<br />Atmosphere<br />The Hydrologic Cycle<br />(water vapor)<br />Flow<br />Precipitation<br />Evapotranspiration<br />( ) = <br />Storage<br />surface<br />Land<br />Streams<br />Oceans<br />Lakes<br />Surface<br />etc.<br />(Ice, snow, <br />depression<br />storage)<br />Overland flow = <br />Compartmentalized<br />Hydrologic<br />Cycle<br />Direct Runoff<br />(Seawater)<br />(Surface water)<br />Infiltration<br />Vadose Zone<br />(Soil moisture)<br />Water Table<br />NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />(Ground water)<br />
- 12. PROCESSES OF HYDROLOGIC CYCLE<br />Precipitation<br />Fall of moisture from the atmosphere to earth surface. Precipitation may be:-<br />Liquid precipitation<br />Frozen precipitation<br />Evaporation and Transpiration<br />Surface Evaporation<br />Water Surface Evaporation<br />Plants/Leaves Evaporation (Transpiration)<br />19<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PROCESSES OF HYDROLOGIC CYCLE<br />Runoff<br />Portion of precipitation that is not evaporated is known as runoff, which ultimately runs to ocean through surface or sub-surface streams. Runoff may be classified as:-<br />Surface runoff<br />Interflow or subsurface runoff<br />Groundwater or base flow<br />20<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PROCESSES OF HYDROLOGIC CYCLE<br />Infiltration<br /> Precipitation falling on the ground, is to some extent, absorbed by the land. This absorption of precipitation water by land from the surface of earth is called infiltration.<br />21<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PROCESSES OF HYDROLOGIC CYCLE<br />Interception<br /> A part of the precipitation is obstructed by vegetation and temporarily remains there. This process is called interception. Later the intercepted water is either evaporated or infiltrated.<br />22<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PROCESSES OF HYDROLOGIC CYCLE<br />Depression Storage<br /> A part of precipitation is stored in depressions on the catchment area. This is called depression storage.<br />23<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>PROCESSES OF HYDROLOGIC CYCLE<br />Detention Storage<br /> When the precipitation occurs for a longer duration and at a rate greater than the rate of infiltration some water is collected on the surface of the earth up to a certain depth. On attaining a certain depth, the action of gravity makes this water flow. Before it starts flowing, the water stored on the surface of earth is called detention storage.<br />24<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>25<br />Engineering Hydrology(CE- 235)<br />HYDROLOGIC EQUATION<br />inflow<br />Storage<br />outflow<br />inflow<br />Law of Conservation of Matter<br />outflow<br />inflow - outflow = D storage<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGIC EQUATION<br />I – O = ΔS (law of conservation of matter)<br /> I = Inflow<br /> O = Outflow<br /> ΔS = Change in storage<br /> In its differential form it states that rate of volume inflow minus the rate of volume outflow is equal to the rate of change of storage. Mathematically<br />I – O = ΔS / Δt<br /> where<br />I = Rate of volume inflow (volume/time), (m3/sec or ft3/sec)<br />O = Rate of volume outflow (volume/time) <br />ΔS / Δt = Rate of change of storage (volume/time)<br />26<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>27<br />Engineering Hydrology(CE- 235)<br />CATCHMENT & BASIN<br /><ul><li>A Catchment is a portion of the earth’s surface that collects runoff and concentrates it at its furthest downstream point, referred to as the catchment outlet.
- 13. The runoff concentrated by a catchment flows either into a larger catchment or into the ocean
- 14. The terms watershed and basin are commonly used to refer to catchments. Generally, watershed is used to describe a small catchment (stream watershed), whereas basin is reserved for large catchments (river basins)
- 15. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />28<br />
- 16. HYDROLOGIC EQUATION<br />Components of Inflow<br />There are two components of inflow:-<br /><ul><li>Precipitation over the catchment and reservoir
- 17. Surface or groundwater flow from other catchment areas</li></ul>29<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGIC EQUATION<br />Components of Outflow<br />Three components of outflow are:-<br /><ul><li>Surface evaporation
- 18. Groundwater seepage
- 19. Direct runoff</li></ul>30<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGIC EQUATION<br /> If we fix the time and take the volume units, then the hydrologic equation can be written as:-<br />Total volume inflow – Total volume outflow =Total change in volume of the system<br /> This is hydrologic or storage equation for a catchment/system<br />31<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>HYDROLOGIC EQUATION<br />Inflows and outflows may or may not change during a time interval of Δt<br />If inflows and outflows changes from ‘I1’ to ‘I2’ and ‘O1’ to ‘O2’ respectively in time ‘Δt’, then the change in storage can be determined by following equation<br />(I1 + I2) / 2 – (O1 + O2) / 2 = (S2 – S1) / Δt<br />32<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>WATER BUDGET IN A CATCHMENT<br />I – O = ΔS<br />P – (Li + R + Le) = D + F<br />or R = P – (Li + Le + D + F)<br />R = P – The Losses<br />R = P - L<br />33<br />Engineering Hydrology(CE- 235)<br />P=Precipitation<br />R=Runoff<br />Li=Loss due to interception<br />Le=Loss due to evaporation<br />D=Depression storage<br />F=storage due to infiltration<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>EXAMPLE # 1<br /> Flow of River Chenab at Marala Barrage varied linearly from 34 cumec (m3/sec) to 283 cumec in 10-hours during a flood. The flow variation at Khanki Barrage, downstream of Marala was observed to be from 28 to 255 cumec during the above mentioned time. Assuming no lateral flow in or out of the reach, find out the rate of change of storage of the river reach between Marala and Khanki. What is the total change in storage of the reach in this period?<br />34<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>EXAMPLE # 2<br /> Water at a constant rate of 370 cumec was observed to be entering into Tarbela Reservoir in a certain season. If outflow from the reservoir including infiltration and evaporation losses is 280 cumec, find out the change in storage of reservoir for 10 such days. Also convert your answer into Hectare-Meter.<br /> (1hec=10000m2)<br />35<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>EXAMPLE # 3<br /> A precipitation measuring 125 mm occurred over a catchment. If the infiltration, interception, depression storage and other losses are 50 mm, find direct runoff and total runoff.<br />36<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>EXAMPLE # 4<br /> A part of catchment area of Hub river measuring 78 km2 received 100 mm of rainfall in 3 hours due to a storm. A drainage stream joins this part of catchment to the Hub river. The stream was dry before rainfall and there was flow in the stream for a period of 2.5 days with an average discharge of 10 cumecs. After the storm runoff, the stream again became dry. Find the losses, direct runoff and total runoff in cumecs and Hectare meter.<br />37<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>EXAMPLE # 5<br /> Assume that Mangla reservoir has surface area of 39 km2 in the beginning of a certain month and the water depth is 76.20 m for this whole surface of the lake. Further assume that sides of the reservoir are nearly vertical. The reservoir received an average inflow of 226.50 cumec as a direct runoff in the same month, and direct precipitation of 125 mm. The outflow from the reservoir was 170 cumec and evaporation and seepage losses were estimated to be 113 mm during the month. Find out depth of reservoir at the end of that month and total increase or decrease in the storage.<br />38<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />39<br />

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