GIS in Water Resources       Homework #4

1.  Given the following grid of elevations, identify any cells that are pits (sinks) in the grid by drawing a circle around the elevation in that cell.  Label the pit cells with the elevation they would have once the pits are filled.  Focus only on the ungrayed center cells.  The grayed edge cells can by definition not be pits because the elevations off the area shown are not known.

 57 55 47 48 48 50 53 53 67 56   A 49 52 54 42 53 52 48 36 37 43 38 51 58 40 42 40 39 38 55 39 38 38 36 38 38

2.  Calculate the slope at grid cell labeled A using

(i)  The standard slope function

(ii)  The 8 direction pour point model

(iii)  The D¥

In these calculations use the pit filled elevation values.

3.  Determine the flow direction grid using the 8-direction pour point method (D8) and pit filled elevations (from part a).   Indicate the flow direction by using an arrow in each cell on the grid below.  Again do this only for the ungreyed center cells as the flow directions for edge cells can not be determined.

Flow direction grid.  Indicate values with arrows.

4.  Determine the flow accumulation grid corresponding to the D8 flow directions.  Label each cell with the number of upstream cells draining into it (ESRI convention), again only for the ungreyed center cells.

Flow accumulation grid, fill in values

5.  If the annual runoff (R) is given by the function R=0.51P-336, determine the annual runoff grid (mm/yr) given the annual rainfall grid below.

Annual Rainfall (mm/yr)

 900 980 1240 1260 1280 1290 1300 950 970 960 980 1050 1100 1180 940 945 950 958 985 1040 1100 860 890 920 940 970 990 1040 830 870 880 900 950 1000 1060

Annual Runoff grid.  Fill in values

 B

6.  If these are 100 m cells calculate the mean annual streamflow draining out of the outlet cell marked B in m3/yr.