SCHEDULE

Discussion Problems Revisiting the road-side ditch question: Water flows faster in ditches than through the soil. If you count the ditch segments that feed directly into streams as part of the stream network, then map the flow length to streams with and without road ditches. By how much is the average flowlength above a stream cell reduced by adding the roads?

Practice Problem Identify FlowDirection for each cell (arrows are okay)

Practice Problem Identify FlowAccumulation(nil)

Practice Problem Identify streams as cells with >10 contributing cells

Practice Problem identify flow distance to streams

OUTLINE EUCLIDEAN: distance allocation direction COST: distance allocation back-direction

Euclidean Distance Shortest distance from the ‘source’ cells to each cell in a grid

Euclidean Distance Shortest distance from the ‘source’ cells to each cell in a grid Example

Euclidean Allocation Identified the nearest ‘source’ cells for each cell in a grid

Angle from each cell in a grid to the ‘source’ cells There may be some use for this Euclidean Direction

Coding Euclidean Distance aGrid.EucDistance (directionFN, allocationFN, maxDistance) aGrid.EucAllocation (distanceFN, directionFN, maxDistance)

Cost Distance The ‘cost’ from moving from one cell to a neighbor is provides the cumulative cost of getting from each cell to the ‘source’ cell with the lowest travel cost to it.

Cost Weighted Averaging The ‘cost’ from moving from one cell to a neighbor is the average of the two values

Cost Allocation The cost grid changes which source area is closest

Back-link Direction The direction to the adjacent cell that leads back to the source grid Does this remind you of anything?

Coding Cost Distance aGrid.CostDistance (costGrid, directionFN, allocationFN, maxDistance) We won’t be getting into using files “…FN” in Avenue We can instead use hydrologic functions to get direction and thus routing.

Discussion Problems We might use stream buffers to disperse sediment and runoff before it reaches the stream. How much larger will a 200’ Euclidean distance stream buffer be than a buffer that includes slopes that have a 200’ flowpath to the stream? How might we use the zonalstats function to quantify the area of each zone?