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Runoff Processes. What happens when we go from a landscape that looks like this … Photo credit: Vermont Land Trust to this? Photo credit: Stowe Mountain.

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Presentation on theme: "Runoff Processes. What happens when we go from a landscape that looks like this … Photo credit: Vermont Land Trust to this? Photo credit: Stowe Mountain."— Presentation transcript:

1 Runoff Processes

2

3 What happens when we go from a landscape that looks like this … Photo credit: Vermont Land Trust to this? Photo credit: Stowe Mountain Resort

4 … or this? Photo credit: U.S. Geological Survey

5 Outline 1. Hydrologic cycle 2. Water balance 3. Effects of landuse change on runoff

6 1. Hydrologic Cycle

7 Hydrologic Cycle Describes the cycling of water through the atmosphere, biosphere and lithosphere. Includes the processes of: Condensation Precipitation Infiltration Evapotranspiration Runoff

8 Condensation: Phase change of water from gaseous to liquid state.

9 Precipitation: Flux of water from atmosphere to earth surface.

10 Evapotranspiration: Flux of water from earth surface to atmosphere. Evaporation: flux from free water surfaces Transpiration: flux from free water surfaces Phase change from liquid to gas Energy consumed in phase change = latent heat

11 Infiltration Influenced by: Soil characteristics Land cover Precipitation rate Vertical movement of water into the soil profile.

12 Runoff Flux of water through the lithosphere to rivers, streams, ocean. Includes: Overland flow Subsurface flow

13 Soil permeability (tendency to soak up water) Rainfall intensity low high lowhigh humid regions arid regions subsurface flow overland flow Adapted from: Dunne & Leopold. Water in Environmental Planning. Geographical patterns in runoff … but how do these patterns in runoff influence landforms?

14 gully erosion from overland flow

15 V-shaped valley of a humid, temperate landscape Photo credit: Field Studies Council, UK Badland topography of an arid landscape Photo credit: National Park Service … landforms reflect dominant runoff processes

16 2. Water Balance

17 Water Balance Describes the relationship among fluxes of water Precipitation Evapotranspiration Runoff

18 Water Balance Land surface Precipitation Evaporation Transpiration Runoff Input Output Land: Precipitation - Evapotranspiration = Runoff

19 3. Effects of landuse change

20 What happens when we go from a landscape that looks like this … Photo credit: Vermont Land Trust to this? Photo credit: Stowe Mountain Resort

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23 Watershed 1, H.J. Andrews Experimental Forest, Oregon

24 Stream gauging station, H.J. Andrews Experimental Forest, Oregon Hydrograph: plot of runoff over time

25 time Runoff A A A B B timeRunoff B Paired watershed studies

26 A A B B Runoff - A Runoff - B Paired watershed studies

27 A A B B time Runoff A timeRunoff B Paired watershed studies

28 A A B B Peak streamflow A Peak streamflow B Before clearing After clearing

29 time Runoff before after Hydrologic effects of deforestation / development Higher peak stream flows Greater annual water yield Lower base flows Faster runoff

30 Hydrologic effects of deforestation First year increases in water yield after forest harvesting Adapted from Hornbeck et al., Journal of Hydrology, 150:

31 Hydrologic effects of deforestation from: Brown et al., A review of paired catchment studies for determining changes in water yield resulting from alterations in vegetation. J Hydrology 310:

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33 Would you expect clearing for ski area development to have the same effects?

34 The Mt. Mansfield paired-watershed study Ranch Brook West Branch

35 Photo credit: Stowe Mountain Resort

36 West Branch watershed Existing Development – 17% cleared Proposed Development* – 24% cleared * with Spruce Peak expansion

37 WY Runoff from ski area and “control” watershed

38 Annual runoff (mm) Clearing for ski areas increases runoff

39 Increase in runoff from ski area development is greater than from traditional forest clearing


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