BAEN 673 / February 18, 2016 Hydrologic Processes

Transcription

1 BAEN 673 / February 18, 2016 Hydrologic Processes Assignment: HW#7 Next class lecture in AEPM 104 Today s topics SWAT exercise #2 The SWAT model review paper Hydrologic processes

2 The Hydrologic Processes

3 The Hydrologic Cycle

4 The Hydrologic Processes

5 The Hydrologic Processes

6 The Hydrologic Processes

7 Hydrologic Processes Movement of water around the globe Very complicated Lots of components Natural and man-made Components are all inter-related What affects one affects all others Spatial and temporal variability Rainfall / land use / soil types / topography / etc

8 Hydrologic Processes Rates are continually changing Hourly rainfall rates Sub-daily high ET during day and almost zero at night Daily air temperatures Seasonally vegetation growth Yearly El Nino weather fluctuations 5 10 year cycle droughts Water has 3 phases Liquid / solid / vapor

9 Global Weather Patterns El Nino the child An irregularly recurring flow of unusually warm surface waters from the Pacific Ocean toward and along the western coast of South America that prevents upwelling of nutrient-rich cold deep water and that disrupts typical regional and global weather patterns La Nina - the (female) child an irregularly recurring upwelling of unusually cold water to the surface along the western coast of South America that often occurs following an El Niño and that disrupts typical regional and global weather patterns especially in a manner opposite to that of El Niño coincides with low rainfall in Texas

10 Natural Components of the Hydrologic Cycle Sun energy source that drives the processes Produces water vapors that are transported around the globe Precipitation rain / snow Meteorology Clouds affects solar radiation / temperature / etc Relative humidity affects PET (arid vs humid regions)

11 Natural Components of the Hydrologic Cycle Meteorology (cont.) Air temperature Wind speed and direction Evaporation From water bodies (especially the sea) From the soil From the vegetation canopy (intercepted water)

12 Natural Components of the Hydrologic Cycle ET Small daily amounts College Station in August approximately 8 mm per day College Station in January approximately 2 mm per day But, over large areas Occurs every day (mostly during the day) More than half of the water that enters the soil is returned to the atmosphere through ET

13 Natural Components of the Hydrologic Cycle Vegetation Transpiration roots mine water from the soil Interception rainfall never hits the ground Interception water is directed along branches to the tree trunk stem flow Protects the soil Litter interflow in forested areas Topography Slope affects runoff rates Determines watershed boundaries

14 Natural Components of the Hydrologic Cycle Topography (cont.) Location of streams Location of surface water bodies Lakes / ponds / wetlands Rainfall patterns orographic effects Latitude (distance N or S of the equator) Length of day Solar radiation Vegetation type

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16 Natural Components of the Hydrologic Cycle: Infiltration The entry of water into the soil Lots of factors influence the rate of infiltration Antecedent moisture content Amount of water already in the soil Soil texture Clays very low hydraulic conductivity (K sat ) Sands very high hydraulic conductivity (K sat ) K sat is a measure of how fast water can move through soil Porosity = the amount of open space in soil

17 Natural Components of the Hydrologic Cycle Surface soils (root zone) Controls infiltration (texture, bulk density, porosity, organic matter, etc) Runoff rates Erosion rates Vegetation types Unsaturated zone Controls infiltration Controls up-flux from the water table

18 Natural Components of the Hydrologic Cycle Unsaturated zone (cont.) Maybe vertical or horizontal flow Clay layer induces horizontal flow Saturated zone Subsurface geology controls groundwater divides Impermeable layers control Unconfined aquifers Confined aquifer Vertical or horizontal flow

19 Natural Components of the Hydrologic Cycle: Groundwater Groundwater recharged by: Water that infiltrates past the root zone Losing streams (in arid regions generally) Groundwater is deeper than the stream This is generally a vertical downward flow path

20 Natural Components of the Hydrologic Cycle: Groundwater Groundwater discharges into: Gaining streams (in humid regions generally) Groundwater is higher than the stream Provides base flow for perennial streams Springs (for example: Comal / San Marcos) Lakes and the sea This is generally a lateral flow process

21 Groundwater In the U.S., drinking water source for 37% of the population Bryan / College Station San Antonio Almost all rural residents In the U.S. in 2010: 61% of groundwater usage was for irrigation 115 billion gallons per day!!

22 Natural Components of the Hydrologic Cycle: Surface Runoff Water that does not infiltrate generally becomes surface runoff Typically conveyed to ditches, small streams, larger streams and eventually to a river Rivers generally flow to the sea

23 Natural Components of the Hydrologic Cycle: Interflow Lateral runoff that quickly moves to a surface water body In forested areas, it is flow that is below the surface but above the soil layer Typical in or under a large litter layer Can occur in soil with a clay layer or bedrock close to the surface Flow along the top of the clay or bedrock

24 Natural Components of the Hydrologic Cycle Streams Discharge points for groundwater in humid regions Gaining streams Recharges groundwater in arid regions Losing streams

25 Gaining streams

26 Gaining and losing stream Dividing line between gaining and losing stream

27 Man-made Components of the Hydrologic Cycle Water use Agriculture Irrigation / livestock / food processing Municipal Drinking water Surface water reservoirs (dams on streams) Groundwater wells Sanitary uses bathrooms / washing / etc Irrigation of landscapes Recreation swimming pools, etc

28 Man-made Components of the Hydrologic Cycle Water use (cont.) Industry Food processing Manufacturing Mining / oil exploration Land management Land clearing changes runoff rates Urbanization suburban sprawl Agriculture / forestry

29 Man-made Components of the Hydrologic Cycle Land management (cont.) Flood protection ponds Large Lake Travis Small many NRCS (SCS) structures Affects stream flows Also used for: Recreation fishing / boating / swimming Drinking water

30 Man-made Components of the Hydrologic Cycle Man-made factors that influence infiltration rate Compaction reduces infiltration Vegetation increases infiltration Human activity Urban developments impervious surfaces Agriculture Surface roughness

31 Hydrologic Modeling Computer simulation is required Approximations must be made Data availability is often limiting Too much data can also be a problem Watershed scale is current modeling trend GIS methods are just becoming available +/- 10% may be the best accuracy we can get

32 Hydrologic Modeling Water quality is a primary concern Water quality modeling requires water flow simulations to be correct first Water quality modeling double the complexity of the modeling effort Very limited water quality data available

33 Class Wrap-up Assignment: HW#7 Next class lecture in AEPM 104