2. Flow Accumulation FE 423 - Lecture 5a

3. Discussion Problems Revisit Practice Midterm with Zonal mean: ([value].ZonalStats(#GRID_STATYPE_MEAN, [zone], Prj.MakeNull, [zone].GetVTab.FindField("Value"), FALSE))

4. Discussion Problems Overlay streamlines and the stream cover on a hillshade of the HJ Andrews dem. Where does the network look wrong? Does filling the dem fixes the problem? Identify and quantify the changes that FILL made.

5. Discussion Problems Road-side ditches can impact watershed hydrology by intercepting surface and subsurface flow and rerouting to the stream. Make a modified flowdirection grid, in which roads intercept downslope flow and route it along the ditch to the streams. Use streamlines to verify that the water now flows the way it should.

6. OUTLINE The take-home midterm Flow Accumulation Stream Networks Stream Order Weighted flow accumulation Watersheds: anti-flowaccumulation

7. SCHEDULE

8. FLOW ACCUMULATION Flow direction Water flows downhill Identifies upslope cells flowGrid.FlowAccumulation(weightGrid) [dem].FlowDirection(ForceEdge).FlowAccumulation (weightGrid)

9. Flow Accumulation

10. STREAM NETWORKS enough water flow to stay open flow increase with upslope area Streams: cells with a minimum value [dem].FlowDirection(ForceEdge).FlowAccumulation(nil) > minCells

11. STREAM ORDER Like Contributing Area aStreamGrid.StreamOrder(dirGrid, shreveMethod)

12. dirGrid.FlowAccumulation(weightGrid) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Weight grid 0 1 0 0 3 12 618 0 WEIGHTED ACCUMULATION The more there is, the more flows downhill

13. WATERSHEDS anti-flowaccumulation From a given outflow, work upslope dirGrid.Watershed(srcGrid)

14. Discussion Problems Revisiting the take-home midterm: Zipping to move your project make directory c:/temp/yourname/flowacc set working directory save project there do some work, then save & close ArcView zip c:/temp/yourname/ move yourname.zip however you like extract yourname.zip to c:/temp/yourname/ double click projectname.apr This is your project, just as you left it.

15. Discussion Problems Revisiting the take-home midterm: Revisable themes look through the themes in the exam Which theme can be revised? Which can’t? What do each group have in common? Rewrite them so that they can be revised Redo the exam assuming everything mature Redo the exam assuming that everything burns Map the mature/burned difference in WAR

16. Discussion Problems Map the stream network from the midterm dem.e00 assuming that all cells with a contributing area of at least 100 cells is a stream cell. What is the area of 100 cells? Make stream networks with different contributing areas. Which one looks best? Make a grid of all stream headwaters (the first cell in each stream).

17. Discussion Problems Runoff from stands in the rain on snow zone is more sensitive to harvest. Streams that have much of their contributing area in the rain on snow zone must be similarly sensitive. If the rain-on-snow zone is 900-1200m, map the fraction of the contributing area of each stream reach that is in the rain on snow zone.

18. Discussion Problems We might want to put special restrictions on the rain on snow slopes above the most sensitive reaches. Identify the stream cells whose contributing area is mostly in the rain-on-snow zone Identify the rain-on-snow cells that contribute to these most sensitive stream reaches.

19. Discussion Problems Revisiting the road-side ditch problem: By how much is the contributing area of each stream cell increased in shifting from natural downhill routing to roadside ditch interception? Does the resulting change look different if you use relative vs. absolute change?