Runoff generation mechanisms

Hillslope Hydrology of Alabama’sSandmountain PasturesRunoff Generation MechanismsSpatial and Temporal Distribution of Runoff Generation AreasPuneet SrivastavaCo-authorsSumit Sen,Kyung H. Yoo,Jacob H. Dane, andJoey N. ShawBiosystems Engineering DepartmentAgronomy and SoilsAuburn University

Presentation Outline• Justification• Runoff Generation Process Concepts• Objectives• Methodology - Instrumentation• Results and Discussion• Runoff generation mechanisms• Spatial and temporal variability of runoff generation areas• Conclusions/Implications of P transport

Justification• Alabama ranks in top three in broilerproduction• About 500 CAFOs and 4000 AFOs;about 12,000 chicken houses• Broiler litter production – 1.8 milliontons/year• Most of the poultry productionoccurs in 5 counties in theAppalachian Plateau (Sandmountainregion)• Land application to pastures - buildup and transport of PTennessee Valley Phosphorusin poultrylitter as apercent ofAppalachian Plateau crop needsin AlabamacountiesBlack Belt soil region0-50%50-100%100-150%150+%

Alabama P-IndexP• Alabama P-Index: Palleviate water quality issues related to Ploss• Based on the principle that P is transported in surface runoff• Agronomic soil P thresholds• Runoff class (hydrologic soil groups)• Soil erosion• P application distance to water• Treats an entire field as runoff (and P) contributing area• Recent studies indicate subsurface transport might beimportant• Runoff might not occur uniformly (spatial and temporally) onthe entire hillslope

Runoff Generation ProcessesInfiltration excess overland flowaka Horton overland flowPPfPfPartial area infiltration excess overland flowPPPfSaturation excess overland flowPPP

Runoff Generation ProcessesSubsurface stormflowPPPPerched subsurface stormflowPPPHorizon 1Horizon 2

Runoff Generation Processes• Factors affecting runoff generation in watershed:• Rainfall characteristics• Soil hydraulic characteristics• Antecedent moisture conditions• Topography• Vegetation• Depth to water table• Presence or absence of restrictive layers (fragipans(fragipans)• Depending on the runoff generation process• Over or underestimation of runoff and P transportpotential• Inappropriate application of BMPs

Objectives• Identify the main surface runoff generation mechanism inthe Sandmountain region of Alabama• Identify spatial and temporal distribution of hydrologicallyactive areas (HAAs) and their connectivity to the outlet

• A pasture hillslope of 0.12 hawas instrumented atSandmountain Research andExtension Center, Crossville,AL• Located in DeKalb County,one of largest poultryproducing counties in AL• Detailed topography• Surface and subsurfacesensorsStudy Site

Study Site

Surface Runoff Sensor• Surface sensors work on“Yes” or “No”

Subsurface Runoff SensorWaterlevel incmVoltage(V)0 2.254 2.009 1.7020 1.5027 1.0040 0.52GroundPin0

Instrumentation

Results and DiscussionRunoff Generation MechanismJune 23, 2006High_intensityshort durationSep 7, 2006Medium_intensitymedium durationOct 27, 2006Low_intensitylong duration

Results and DiscussionRunoff Generation MechanismDisk infiltrometer(Decagon, Inc.)Low (0 – 5.0 mm/hr)Medium (5.1 – 20.0 mm/hr)High ( > 20.1 mm/hr)

Results and DiscussionRunoff Generation MechanismR a in fa ll (m m/hr)9080706050403020100151015201530154015501600Time (hh:mm)High intensityshort-durationSummer Precipitation16101620163016401650

Results and DiscussionRunoff Generation Mechanism• Location 4 (measured soil hydraulic conductivity 11.1 mm/hr)321!( 12!(3 4!( !(320.55 6!( !(7!(8!(0.1 m Contours3209!(10!(11!(Hillslope Drainage BoundaryHydraulic Conductivity!( High!( Medium!( Low319.5!(12 13!(15!(14!(17!(1621!(!(20!(!(19 29!( !(2531!(18 28!( !( 23 !(!( 30!(24!(319318.50 3.75 7.5 15 22.5 30¸26!(318.1Meters27!(Time(hhmm)IncrementalRainfall(mm)RainfallIntensity(mm/hr)SubsurfaceSensor - Depthto water table(cm)Surface Sensor -RunoffOccurrence(yes/no)1510 2.54 30.5 42 Yes1520 5.33 64.0 40 Yes1530 1.52 18.3 40 Yes1540 0.508 6.1 27 Yes1550 0.00 0.0 40 YesInterpretationInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoff

Results and DiscussionRunoff Generation Mechanism• Location 6 (measured soil hydraulic conductivity 51.2 cm/hr)321!( 12!(3 4!( !(320.55 6!( !(7!(8!(0.1 m Contours3209!(10!(11!(Hillslope Drainage BoundaryHydraulic Conductivity!( High!( Medium!( Low319.5!(12 13!(15!(14!(17!(1621!(!(20!(!(19 29!( !(2531!(18 28!( !( 23 !(!( 30!(24!(319318.50 3.75 7.5 15 22.5 30¸26!(318.1Meters27!(Time(hhmm)IncrementalRainfall(mm)RainfallIntensity(mm/hr)SubsurfaceSensor - Depthto water table(cm)Surface Sensor -RunoffOccurrence(yes/no)1510 2.54 30.5 42 Yes1520 5.33 64.0 4 Yes1530 1.52 18.3 4 Yes1540 0.508 6.1 4 Yes1550 0.00 0.0 4 YesInterpretationInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoffInfiltration excessrunoff



Results and DiscussionRunoff Generation MechanismR ainfall (m m /hr)20181614121086420161516301645170017151730Medium intensitymedium-durationFall Precipitation1745Time (hh:mm)180018151830184519001915Sen, S., P. Srivastava, K. Yoo, J. Dane, J. Shaw, andM.S. Kang. 2008. RUNOFF GENERATIONMECHANISMS IN PASTURES OF THE SANDMOUNTAIN REGION OF ALABAMA – A FIELDINVESTIGATION. Hydrological Processes (In Press)R ain fall (m m /h r)Similar analyses for Sep 7, 2006 (medium intensity,medium-duration) and October 22, 2006 (lowintensity, long-duration)76543210Low intensitylong-durationWinter Precipitation2053104155206257308359401045115012551400150516101730183519402045Time (hh:mm)

Results and DiscussionSpatial and Temporal Distribution and ConnectivityRainfall (mm/hr)908070605040302010015101520153015401550June 23, 2006 Event16001610Time (hh:mm)1620163016401650Discharge (m 3 /min)8.0E+007.0E+006.0E+005.0E+004.0E+003.0E+002.0E+001.0E+000.0E+001510154016101640171017401810184019101940Time (HH:MM)2010204021102140100% of the total areawas contributingsurface runoff29% of the total areawas contributingsurface runoff

Results and DiscussionSpatial and Temporal Distribution and ConnectivityRainfall (mm/hr)6050403020100July 20, 2007 EventDischarge( m 3 /m in)4.0E-023.5E-023.0E-022.5E-022.0E-021.5E-021.0E-025.0E-030.0E+0010401050110011101120113011401150120012101220123012401250104010501100111011201130114011501200121012201230Time (hh:mm)Time (hh:mm)49% of the total areawas contributingsurface runoff100% of the total areawas contributingsurface runoff

Results and DiscussionSpatial and Temporal Distribution and ConnectivityRainfall (mm/hr)6050403020100Discharge( m 3 /m in)4.0E-023.5E-023.0E-022.5E-022.0E-021.5E-021.0E-025.0E-030.0E+0010401050110011101120113011401150120012101220123012401250104010501100111011201130114011501200121012201230Time (hh:mm)Time (hh:mm)73% of the total areawas contributingsurface runoff41% of the total areawas contributingsurface runoff

Results and DiscussionSpatial and Temporal Distribution and ConnectivitySen, S., P. Srivastava, K. Yoo, J. Dane, J. Shaw, and M.S. Kang. 2008. SPATIAL AND TEMPORAL DYNAMICS ANDCONNECTIVITY OF RUNOFF CONTRIBUTING AREAS IN PASTURES OF THE SANDMOUNTAIN REGION OFALABAMA – A FIELD INVESTIGATION. Hydrological Processes (In preparation)

Conclusions• Surface runoff generation mechanism was mostly infiltrationexcess in the Sandmountain pasture of Alabama.• Rainfall intensity and soil hydraulic conductivity controlsurface runoff generation.• At times (when the rainfall intensity is high), surface runoffcan be generated from the entire hillslope.• Connected areas of low soil hydraulic conductivitycontribute most of the surface runoff at the outlet.• Overall, preliminary analysis shows that during high-intensity short and medium duration rainfalls no more than10% of the rainfall results in surface runoff at the outlet.• For medium-intensity, intensity, long duration rainfalls no more than5% of the rainfall results in surface runoff

Implications and Future Work• Since surface runoff contributions to the outlet is small –significant infiltration occurs, highlighting the importance ofunderstanding subsurface flows and subsurface transport.Subsurface stormflowPPPPerched subsurface stormflowPPPHorizon 1Horizon 2

Implications and Future Work• Quantification of surface and subsurface flows through 2-D 2modeling• Quantification of leaching of P from surface and subsurfaceapplied broiler litter – Field investigation• New and improved BMPs that take into account the major Ptransport pathway is needed.• Alabama P-index Pmight need to be revised.

Runoff generation mechanisms

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