The hydrologic analysis was conducted to determine the average precipitation and snowmelt that flows into the detention tanks. The client provided a NAU Stormwater Drainage Report, which specifies the drainage basins of the location of each drainage basin in relation to the project location. The basins represent drainage areas for stormwater runoff that is collected in the detention tanks. The area for each basin is shown below in Table 1.
| Basin Number | Drainage Area (acres) |
|---|---|
| 1 | 2.15 |
| 2 | 0.64 |
| 3A | 0.20 |
| 3B | 0.18 |
| 4A | 1.22 | 4B | 2.40 |
| 5 | 1.40 |
| Total | 8.19 |
The hydrologic analysis also includes finding the average precipitation and snowmelt over a period of two years as suggested by the client. The average precipitation and snowmelt data were analyzed for year 2016-2017 in Flagstaff, Arizona from US Climate Data. The snowmelt was converted to liquid water, since every ten inches of snow is roughly one inch of rain. The precipitation and snowmelt were added together to make the water equivalent. Then the data recorded were converted to feet. The precipitation/snowmelt was then multiplied by the total drainage area of the basins, above, to determine the volume of rain for each month of 2016 and 2017. This is shown in the following Table.
| Month/Year | *Water Equivalent (ft) | Average Daily Volume (gal) |
|---|---|---|
| Jan-16 | 0.47 | 41,436 |
| Feb-16 | 0.11 | 9,859 |
| Mar-16 | 0.04 | 3,262 |
| Apr-16 | 0.11 | 10,007 |
| May-16 | 0.18 | 16,159 |
| Jun-16 | 0.08 | 7,264 |
| July-16 | 0.43 | 38,027 |
| Aug-16 | 0.25 | 22,608 |
| Sep-16 | 0.18 | 16,382 |
| Oct-16 | 0.07 | 6,597 |
| Nov-16 | 0.31 | 27,204 |
| Dec-16 | 0.40 | 35,951 |
| Jan-17 | 0.39 | 34,320 |
| Feb-17 | 0.00 | - |
| Mar-17 | 0.31 | 27,204 |
| Apr-17 | 0.02 | 1,483 |
| May-17 | 0.02 | 2,076 |
| Jun-17 | 0.00 | - |
| July-17 | 0.66 | |
| Aug-17 | 0.36 | 31,652 |
| Sep-17 | 0.07 | 6,078 |
| Oct-17 | 0.00 | - |
| Nov-17 | 0.00 | 371 |
| Dec-17 | 0.00 | - |