| Flood Impacts |
| 39.2 | This level is expected to be met or exceeded on average once every 500 years. |
| 38.2 | This is the RECORD FLOOD LEVEL that was reached on August 1 1993. |
| 37.4 | This level is expected to be met or exceeded on average once every 200 years. |
| 35.2 | This river level is expected to be exceeded once in every
100 years. |
| 33.5 | Nutwood Levee is Overtopped |
| 33.1 | This flood level was reached on April 28 1973. |
| 33.0 | Water Treatment plant is inundated |
| 32.9 | This river level is expected to be exceeded once in every 50 years. |
| 32.1 | Methodist Church at Main St. and Vine St. begins flooding. |
| 32.0 | Runways and Hangers at Smartt Airfield are flooded. |
| 31.0 | The hanger at the north end of Smartt field begins to flood |
| 30.4 | This level is expected to be met or exceeded on average once every 25 years. |
| 29.5 | This level is expected to be met or exceeded on average once every 20 years. |
| 29.1 | Water reaches Main at Church Street |
| 29.0 | Route 100 between Grafton and Alton inundated. This is also designated as the Major flood level. |
| 28.5 | The Northwest and Northeast corners of Smartt Field are flooded |
| 28.4 | Water reaches Main Street at the Vistors Center |
| 28.3 | Water reaches the intersection at Main & Route 100. Also at this level the Northeast Corner of Smartt Airfield begins flood. |
| 27.6 | Beasleys Fish Market at Main & Overmeyer floods. |
| 27.5 | Majors Motel at Main & Dagget Hollow floods |
| 26.4 | Residential flooding in Grafton occurs |
| 26.0 | Water distribution system begins to flood so emergency measures begin. |
| 25.7 | This level is expected to be met or exceeded on average once every 5 years. |
| 25.6 | Gables Resturant at Main & Sycamore floods |
| 25.5 | Brussels Ferry closes. |
| 25.2 | West End Fish Market at Main & Canal floods. |
| 24.7 | City of Grafton closes Route 100. Also at this level the Catholic Church at Main & Evans floods. |
| 24.0 | Route 100 inundated at Chautaqua and Elsah. This is also designated as the Moderate flood level. |
| 23.8 | Main Street... Route 100... is inundated |
| 23.5 | Flooding begins to overtop the Levee in West Alton. |
| 21.5 | In Portage des Sioux, MO, Le Sieur Street leading to the Marina and to Our Lady of the River Statue is flooded. |
| 20.4 | This level is expected to be met or exceeded on average once every 2 years. |
| 18.0 | Flood Stage. Right bank begins to over flow... flooding farmland. |
| 16.2 | For navigational purposes through Alton Lock and Dam control, the Corps will not allow the river to exceed this level, if at all possible. |
| 14.2 | For safe navigation of barge traffic, the Corps will try to keep the river above this level. |
