A-11 
Simple Numerical CFD Example 
For this example, assume a segment for which the interpolation grid is 4 cells by 4 
cells. In reality, the number of grid cells is much larger. Also let data be collected on 
5 dates. Typically data would be monthly for a total of 36 dates. Let the criterion 
threshold for this fictitious water quality parameter be 3. In what follows, you will 
Find an illustration of the steps of computing the CFD for these simplified 
constraints. The three columns of the next page show the first three steps. Column 
I shows fictional data for five dates for five fixed locations in a 2 dimensional grid. 
Column 2 shows a fictional interpolation of these data to cover the entire grid. 
Column 3 shows the compliance status of each cell in the grid where 1 indicates 
noncompliance and 0 indicates compliance. 
Step 1. Collect data at 
known locations. 
date 1 
3 
3 
5 
2 
1 
date2 
1 
1 
3 
1 
1 
date3 
4 
2 
2 
1 
1 
date4 
1 
4 
2 
4 
1 
date5 
1 
3 
2 
1 
1 
Step 2. Interpolate the 
data to grid cells. 
date 1 
3 
4 
5 
3 
4 
4 
5 
2 
3 
3 
4 
1 
2 
3 
3 
1 
date2 
1 
2 
3 
1 
2 
2 
3 
2 
1 
3 
2 
1 
1 
1 
1 
1 
date3 
4 
3 
2 
2 
3 
2 
2 
1 
2 
2 
1 
1 
1 
1 
1 
1 
date4 
1 
2 
3 
4 
2 
2 
2 
3 
3 
3 
2 
1 
4 
3 
1 
1 
date5 
1 
2 
3 
3 
9 
Z. 
2 
2 
2 
1 
1 
1 
1 
1 
1 
1 
1 
Step 3. Determine 
compliance status of each 
cell. 
date 1 
1 
1 
1 
1 
1 
1 
1 
0 
1 
1 
1 
0 
0 
1 
1 
0 
date2 
0 
0 
1 
0 
0 
0 
1 
0 
0 
1 
0 
0 
0 
0 
0 
0 
date3 
1 
1 
0 
0 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
date4 
0 
0 
1 
1 
0 
0 
0 
1 
1 
1 
0 
0 
1 
1 
0 
0 
date5 
0 
0 
1 
1 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
appendix a 
The Cumulative Frequency Diagram Method for Determining Water Quality Attainment 
