Presentation on theme: "The Hillslope-Stream Continuum Wed 4/22/2009. "The El Nino-Southern Oscillation and Global Precipitation Patterns: A View from Space" Dr. Scott Curtis."— Presentation transcript:
"The El Nino-Southern Oscillation and Global Precipitation Patterns: A View from Space" Dr. Scott Curtis Assistant Director Center for Natural Hazard Research Department of Geography East Carolina University WEDNESDAY, APRIL 22nd at 3:30 TOY LOUNGE, DEY HALL
How does rainfall become streamflow? Bear Brook, ME Is pH just an episodic depression?
Bear Brook, ME If so, why do values stay low after the event? Why aren’t the variations in streamflow reflected in pH?
Streamflow Components Terms Event water- water that enters the catchment during Pre-Event water- any water that resided in the catchment prior to event
Storage Reservoirs Catchment components can be considered storage reservoirs For example- Groundwater and Surface water So for a long time it was assumed that quickflow was rain, slowflow was groundwater
Quantifying hydrograph separations using chemical or isotopic tracers Assume: 1)old water is fairly constant in space and time, 2)Concentration in precipitation is constant over the course of the event Qt= Total Streamflow Qo= Pre-event water Qn= Event water Ct= Streamflow concentration Co= Concentration in groundwater Cn=Concentration in rain
Meaured chloride concentration during the peak of the rainstorm event Rainfall [Cl] =Cn= 4.5umol/L Groundwater [Cl]= Co= 40.5 umol/L Streamflow [Cl]= Ct = 36.0 umol/L What fraction of total streamflow is contributed by new and old water?
How does it get there? Various mechanisms of Streamflow Generation
Baseflow streamflow maintained by groundwater contributions Stormflow Augmented by direct precipation Overland flow Infiltrating rainwater- return flow Shallow subsurface stormflow
Terms Overland flow – Infiltration-excess overland flow- runoff generated where infiltration capacity is exceeded by rainfall intensity – Saturation-excess overland flow- runoff generated where shallow water table intersects ground surface Return flow- groundwater reemerges from the soil at a saturated area and flows downslope as overland flow
Dominant Runoff Processes Horton Overland Flow Dominates Subsurface flow less important Direct Precipitation & Return Flow Dominate Subsurface stormflow dominates Peaks produced by return flow & Direct precipitation Variable Source Area Climate, Vegetation, & Land Use Topography and Soils Thin Soils Gentle slopes Wide Valley Bottoms Steep straight slopes Narrow Valley Bottoms Humid Climate Dense Vegetation Arid to Semi-Arid Sparse Vegetation Urbanizing
Topographic (Wetness) Index TI= ln( a/ Tan B) Where: a= upslope contributing area B= local slope
some equations Soil moisture defecit=s Depth of water you’d need to add To reach ground surface
Tmax = Transmissivity. Recall T = KB K=hydraulic conductivity B= soil (aquifer) depth To simplify- assume soil is saturated m=curve fitting parameter. If T decreases rapidly with depth, m Will be large. A small value of m means T decreases slowly with depth
TOPMODEL SIMULATIONS Alter Tmax and m Effect of TI distribution
Remaining soil moisture utilized by vegetation- canopy growth Balance of two major forces: gravity, ET
Links to water quality Timing matters- implications for when DOC Higher [DOC] in summer months- implications for water managers
Future Directions: Double Paradox 1)Rapid Mobilization of ‘old water’ 2)Variable chemistry of old water Kirchner, 2003 HP