Introduction

1. Introduction WATERSHED MODELING Lecture 1 HID, USPCASW, MUET, Jamshoro

2. Learning outcomes • At the end of this lecture students will be able to; • KNOW – the definition of Hydrology • LEARN – the components of Hydrologic cycle • KNOW – what is meant by hydrologic analysis

3. Hydrology: Definition Natural Science that deals with the transport and distribution of water (liquid, gas, solid) in the atmosphere, on and beneath the earth's surface

4. Hydrology • Study of: • Occurrence • Circulation • Storage • Quality • Distribution of surface and ground water on the earth

5. Hydrologic data required? • Climatological data • Hydro-meteorological data • Precipitation records • Stream-flow records • Seasonal fluctuation of GW table • Evaporation data • Cropping pattern, crops and their consumption • Water quality data (both surface and GW) • Etc.

6. Why we need to manage WORLD’S WATER RESOURCES?

7. Distribution of Earth Water Resources

8. 1.4 billion Km3 of water on Earth Water Inventory at Earth's Surface http://www.livinglandscapes.bc.ca/thomp-ok/env-changes/water/introduction.html

11. Global Water Usage Trend • Accelerating • 1975: 700 km3/y • 2000: 3700 km3/y • Causes • PopulationIncrease • Better Living Standards • Others

12. Hydrologic Cycle • Continuous process • Water evaporates from water surfaces • Moves inland as moist air masses • Precipitation falls from clouds

13. Hydrologic Cycle Water is conserved: Neither created nor destroyed

14. Components of Hydrologic Cycle Quantity of each component depends on?

15. Components of Hydrologic Cycle • Precipitation • Major element that drives Hydrologic Cycle depending on various weather parameters and systems • Infiltration • Function of soil moisture conditions and soil type • Runoff • Overland flow in a down gradient direction

16. Components of Hydrologic Cycle • Storage • Surface and groundwater • Evapotranspiration • Evaporation: the conversion of water to water vapor from a water surface • Transpiration: loss of water vapor through plant tissues and leaves

17. Hydrologic Analysis • Hydrologic analysis is done to determine rainfall-runoff response from a watershed area • Hydrologic Cycle is a complex series of processes but under well defined conditions with simple assumptions the response of a watershed can be known

18. Precipitation • When atmospheric moisture becomes so heavy to remain suspended in clouds • All form of water that comes to earth from atmosphere (rainfall, snowfall, hail, frost, and dew) • Rainfall is the predominant form • Ocean evaporation is the greatest source (90%)

19. Precipitation is Variable !!! • Example: Year to year variation

20. Source: Global Precipitation Climatology Project (GPCP) by GEWEX Radiation Panel (GRP)

23. Surface Runoff • Water that flows over land after storm events: Quantity depends on: • Climatic Factors: • Rainfall frequency and intensity • Geological Factors: • surface permeability • Geometrical Factors: • shape of watershed, slope • Biological Factors: • Vegetation cover • Zero runoff? • Runoff = rainfall?

24. Storage: Surface Water Surface water • Reservoir: Artificial or naturally inland body of water used to store water to meet various demands • Lake: Large naturally occurring inland body of water • Wetlands: Natural or artificial areas of shallow water or saturated soils that support certain water plants

25. Storage: Groundwater • Water infiltrating through soil cover of a land surface to a huge waterbody underground • In a state of continuous movement • Difficult to extract all by practicable means • Groundwater recharge: replenished by precipitation, seepage from surface waterbodies, conveyance system return flow from irrigation water. • Governed by rainfall intensity and soil and aquifer conditions

26. Evapotranspiration • Combination of Evaporation and Transpiration

27. Watershed • the geographical area that contributes to the flow of a river • Basic hydrologic unit within which all measurements, calculations, and predictions are made in hydrology • To calculate runoff (volume) expected from a given rainfall event that falls over an area • Varies in size from few acres to thousands of square miles

29. Watershed • Watershed delineation based on topographic or elevation data • Watershed divide (ridge line) separates two watersheds that drain into different outlets • Area encompassed by divide is the watershed area • Runoff originating at higher elevations moves towards lower elevation in a direction perpendicular to the contour lines to the nearest stream • Larger the watershed area greater the surface runoff rate and stream flow rate

30. Hyetograph? • Distribution of rainfall over time

31. Isohyetal maps

32. Isohyetal maps

33. Hydrograph • Hydrologic response of rainfall at the outlet of an area • A plot of discharge in the channel vs. time (cubic feet per second)

34. Hydrograph response shape depends on?

35. Effect of Basin Characteristics on the flood hydrograph

36. Impact of Urbanization ?

37. Water Resources Potential (WRP) Utilizable surface water potential: amount of water that can be fully used without wastage to sea

38. Future Development of Water Resources • Sustainable water utilization • Conservation of water (cleaner practices) • Non-consumptive use

39. DISCUSSION&Questions