What is hydrology? The term comes from the Greek: ὕ δωρ “hydōr” = water + λόγος...
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What is hydrology? The term comes from the Greek: hydr = water + logos = study or knowledge of. Sub-disciplines: Hydrometeorology, climatology, oceanography, limnology, potamology, hydrography, hydrogeology, geomorphology, hydrogeochemistry, hydropedology, ecohydrology, hydroecology, hydraulic engineering, etc. Is an important part of most disciplines: Agriculture, biology, engineering (civil, geotechnical, mechanical and mining), geology (exploration, petroleum, environmental, mine), natural resource management (catchment, environment), urban planning, economics, politics, history, etc. Water sourceVolume (km 3 )Percent Oceans, seas & bays1,338,000, Ice caps, glaciers & snow24,064, Groundwater23,400, Fresh(10,530,000)(0.76) Saline(12,870,000)(0.94) Ground ice & permafrost300, Lakes176, Fresh(91,000)(0.007) Saline(85,400)(0.006) Soil moisture16, Atmosphere12, Swamps11, Rivers2, Plants & animals1, Total1,386,000, Global water budget (Gleick, 1996) Lets say that the global water budget was represented by 100 stubbies of ginger beer (8 dozen and four stubbies) Of the remaining stubby, some of it is salty or contaminated That leaves less than half a glass of amber fluid immediately available to quench your thirst. The eight dozen represent the salt water in the ocean (you cant drink them) Of the remaining 2 stubbies, 1 represent the groundwater (you cant see the beer) Of the remaining 4 stubbies, 2 represent the frozen water (you cant drink them either) Catchment scale An open system Because the hydrologic cycle circulates water within human time-frames, groundwater is generally regarded as a sustainable resource. Hydrology is classic Systems Science. Hydrologic Equation: Input Output = Change in Storage I O = S Gaining stream receives groundwater baseflow into the stream Losing stream leaks surface water into the groundwater storage Groundwater dependent rivers Most rivers south west Victoria depend on groundwater for environmental flows Barwon RiverNaringhil Creek Scotsburn rainfall recordWest Moorabool River catchment Data source: Bureau of Meteorology Climate change? Among geologists its a contentious debate Question is: Our climate may be warming, but is it because of our activities, or is it natural? Not being sure is not an excuse to do nothing The Earths geological record shows huge variation in magnitude, frequency and amplitude of climatic change. Some of this may be related to the effects of other species Water Consumption in Victoria Irrigation 76.2% Farm & stock 4.4% Melbourne urban 11.0% Regional urban 5.4% LaTrobe Valley industry 3.0% We use more than 80% of our water to grow plants World Water Council There is a water crisis today. But the crisis is not about having too little water to satisfy our needs. It is a crisis of managing water so badly that billions of people and the environment suffer badly (2000) Water value Drinking water most beneficial use Ranges from $2/1l bottle to $1/Kl or $0.001/l Urban supply $0.001/l Irrigation/industrial/dairy $3/Ml or $ /l Plus pumping costs Domestic/stock Desalinisation - $1500/ML Aesthetic - tourism Environmental flows H 2 O facts 50% of the worlds wetlands have disappeared in the last century 3,900 children die each day from water borne diseases 1.1 billion live without clean drinking water Daily per capita use of water in residential areas: 200 litres in Europe 350 litres in North America and Japan 10-20 litres in sub-Saharan Africa What controls where rain falls? Highly variable distribution At all scales country to backyard variation Altitude, aspect, slope, ocean temperature Cooler airWeather direction Measurement, angle of rain About Units... Some hydrologic processes are measured by depth and others by volume. Rainfall and evaporation are measured by depth (usually millimetres) One cubic metre (m 3 ) = 1000 litres One millimetre depth over one hectare = 10m 3 10cm depth over one hectare = 1000m 3 = 1Megalitre (ML) Rainfall and evaporation are also by rate (mm/hour, mm/day, mm/year) Measuring precipitation Standard rain gauge Pluviometer World Meteorological Organisation (WMO) Automated recording of several measurements Phone or telemetry reading Evaporation Pan Pan reading over 24 hours (minus rainfall input) ET = Pan reading x Pan factor Pan factor ~ 0.5 to 0.8 usually ~ 0.75 Pan Evaporation conversion to Evapotranspiration Direct measurements Weight changes Deep drainage E T = S i + P R + I R S f - D E E T = Evapotranspiration in a given time period S i = Initial soil water volume S f = Final soil water volume P R = Precipitation into lysimeter I R = Irrigation water into lysimeter D E = Drainage of water from lysimeter I O = S Hydrologic equation Runoff Volume of runoff depends on: Rainfall intensity and duration Type of surface (pervious or impervious) Area of catchment Nolans Road, Napoleons, Vic. February 2005 Low intensity rainfall = infiltration High intensity rainfall = infiltration + runoff Runoff surface Thick vegetation = low volume, slow runoff Paved area = high volume, fast runoff Rational Equation The rational method is used around the world for peak flow estimation of small rural drainage basins and is the most widely used method for urban drainage design. The rational method equation is given below: Q = kCiA where: Q - peak flow (m 3 /s). k - conversion factor equal to (metric). C - dimensionless runoff coefficient. i - rainfall intensity (mm/hr). A - catchment area (ha). Measuring Runoff Q = vA Q = Discharge (m 3 /s) V = velocity (m/s) A = Cross sectional area (m 2 ) Measurement techniques weirs price current meters dilution gauging moving boat method ultrasonic velocity probe electromagnetic volumetric rising air float width contractions culverts equations Measuring streamflow velocity Float & stopwatch Current meter Ultrasonic flow gauge factors affecting flow in stream channels cross-sectional dimensions cross-sectional shape slope boundary friction Measuring flow Q = v A = v i A i = v i b i h i (where A i = b i h i ) vivi bibi Stream bed profile Plan view across measuring line hihi Curdies River gauge, Heytesbury region, Vic Gauging Stations Stream gauges - components V-notch weirs 90 o V-notch weir Q = H 5/2 Q = discharge (m 3 /s) H = height of water (m) Cheap, reliable, easy to install, accurate Flow calculations (hydraulics) Manning equations Mannings Coefficient Gravel0.025 with boulders0.04 earth0.05 concrete smooth0.012 rough0.015 Example - Wide River P=B+2H=24m A=BH=20(2)=40m R=A/P=40/24=1.67m v=(1/n)R 2/3 S 1/2 =(1/.03)(1.67) 2/3 (.0002) 1/2 =.67 m/s = 67 cm/s B H A S=.0002, H=2m B=20m, n=0.03 Rainfall (mm) time Discharge m 3 /hr Rising limb Falling limb Peak discharge Lag time Groundwater baseflow Storm flow Varying flow conditions A stream may switch from a gaining stream during low flow conditions to a losing stream during flood conditions Hydrograph development depends on the: Rainfall intensity Infiltration rate Volume of water infiltrated Soil moisture deficiency