1. SURFACE HYDROLOGY and HYDROLOGIC FUNCTIONS
FE423 - February 3, 2000

2. OUTLINE
Your labs
Hydrologic processes
Hydrology in GRID

3. Labs automate.aml vs. valley_fill.aml
fill%i% = con(dem > %i%,dem,%i%)
automate.aml vs. valley_fill.aml
Discuss function and workings of macros
Do and write your lab simultaneously

4. Hydrology

5. Hydrology water flows down hill (and payday is on Friday)
many processes increase as Slope & Area
surface erosion
stream power
landsliding

6. Doing Hydrology in GRID
Flow Direction depends on local slope
Flow is accumulated at each point
along with everything it carries
Streams require minimum flow
The watershed is the cells upslope
Stream Order is a measure of accumulation
Delivery to streams decreases with distance
We can convert stream cells into arcs

7. Flow Direction (hint: downhill)
The steepest downhill gradient.

8. Flow Accumulation

9. Accumulating Stuff Weight grid 1 1 1 1 1 1 1 1 1 1 3 1 1 1 12 1 1 12 11 1 1 1 1 1 1 1 3 1 1 1 12 1 1 12 1 1 1 1 6 18
Weight grid

10. Streams Minimum Contributing Area Minimum Stream Power
stream = con(flowaccumulation > min_area)
Minimum Stream Power
stream = con(fa * slope(dem) > min_sp)

11. Sinks Sinks are commonly viewed as errors
Sinks can be an artifact of the gridding process
Sinks are filled with the FILL command

12. Watershed (anti-accumulation)

13. Stream Order An old version of Flow Accumulation
Shreve counts headwaters
Strahler counts in a log fashion.

14. Flow Distance
Filtering effects increase with distance

15. Linearizing Stream Networks