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The Hillslope -Stream Continuum

The Hillslope -Stream Continuum. Wed 4/22/2009. "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

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The Hillslope -Stream Continuum

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  1. The Hillslope-Stream Continuum Wed 4/22/2009

  2. "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

  3. How does rainfall become streamflow? Bear Brook, ME Is pH just an episodic depression?

  4. If so, why do values stay low after the event? Why aren’t the variations in streamflow reflected in pH? Bear Brook, ME

  5. Two Hydrograph Components:Quickflow baseflow

  6. Streamflow Components Terms Event water- water that enters the catchment during Pre-Event water- any water that resided in the catchment prior to event

  7. 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

  8. Sources of water

  9. Quantifying hydrograph separations using chemical or isotopic tracers Qt= Total Streamflow Qo= Pre-event water Qn= Event water Ct= Streamflow concentration Co= Concentration in groundwater Cn=Concentration in rain Assume: old water is fairly constant in space and time, Concentration in precipitation is constant over the course of the event

  10. 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?

  11. Rainfall [Cl] =Cn= 4.5umol/L Groundwater [Cl]= Co= 40.5 umol/L Streamflow [Cl]= Ct = 36.0 umol/L Qn = (36-40.5)/ (4.5-40.5) * Qt

  12. How does it get there? Various mechanisms of Streamflow Generation

  13. Baseflow streamflow maintained by groundwater contributions Stormflow Augmented by direct precipation Overland flow Infiltrating rainwater- return flow Shallow subsurface stormflow

  14. 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

  15. Streamflow Generation • Direct precipitation onto stream channel • Overland Flow • Shallow Subsurface Stormflow • Groundwater Flow

  16. Dominant Runoff Processes Thin Soils Gentle slopes Wide Valley Bottoms Direct Precipitation &Return Flow Dominate Horton Overland Flow Dominates Subsurface flow less important Variable Source Area Topography and Soils Subsurface stormflow dominates Peaks produced by return flow & Direct precipitation Steep straight slopes Narrow Valley Bottoms Humid Climate Dense Vegetation Arid to Semi-Arid Sparse Vegetation Urbanizing Climate, Vegetation, & Land Use

  17. Factors controlling variable source area

  18. TOPMODEL • Numerical model for routing water through a catchmentto predict hydrographs • Based on catchment characteristics • Fundamental streamflowgeneation mechanism- saturation excess overland flow

  19. Hillslope Water Balance

  20. Topographic (Wetness) Index TI= ln( a/ Tan B) Where: a= upslope contributing area B= local slope

  21. some equations Soil moisture defecit=s Depth of water you’d need to add To reach ground surface

  22. 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

  23. TOPMODEL SIMULATIONS • Alter Tmax and m • Effect of TI distribution

  24. Remaining soil moisture utilized by vegetation- canopy growth Balance of two major forces: gravity, ET

  25. Links to water quality Timing matters- implications for when DOC Higher [DOC] in summer months- implications for water managers

  26. Future Directions: Double Paradox Rapid Mobilization of ‘old water’ Variable chemistry of old water Kirchner, 2003 HP

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