NOAA's gauge page for the White River at Anderson, at the Raible Avenue gauge, lists major flooding at 18 feet. Flood stage is a threshold on the gauge, not a measure of damage, and gauge zero points differ between sites and years, so a historical figure must be checked before it is compared with a current reading.
Key takeaways
- NOAA's gauge page for the Raible Avenue gauge in Anderson lists major flooding at 18 feet.
- A gauge reading is the height of the water surface at one fixed point, and a flood stage is a threshold on that reading.
- A forecast crest and an observed crest are different things, and a reader should check which one a figure describes.
- The 1913 crest was recorded on the gauge then in use, so its figure must be checked against that gauge's zero point before comparison.
- A stage threshold says when the river begins to cause specific effects; it does not say what a single basement will receive.
- A reader who wants the current level can check the gauge page directly, rather than relying on a figure from a previous year.
What does a river gauge reading actually measure?
A river gauge reading is the height of the water surface at one fixed point, measured against a zero reference set for that gauge. It tells you how high the water is at that spot at that time, and nothing more about the river or the houses around it.
A gauge is usually a graduated scale or a sensor installed in the water at a bridge, a pier or a bank. The reading it gives depends on the water surface at the gauge, which can differ from the surface a few hundred meters upstream or downstream. A reading is therefore specific to its location, and a reader should not assume that the water at a house is the same height as the water at the gauge.
The zero reference is the key to reading any gauge. Two gauges on the same river can give different numbers for the same water surface, because their zero points are set differently. The figures on a gauge page are only comparable with other figures from the same gauge, unless the page explains a conversion.
What is a flood stage, and why does a figure like 18 feet matter?
A flood stage is a threshold on the gauge at which the river begins to cause a defined effect. NOAA's gauge page for Anderson lists major flooding at 18 feet, which marks the height at which the published guidance expects major impacts to begin.
Flood stages are set by the agency that runs the gauge, usually with a set of thresholds for minor, moderate and major effects. Each threshold describes what the water is expected to do, such as covering a road, a park or a low area. The number tells a reader when the river has reached that effect, not how much damage a particular building will take.
The 18-foot figure is therefore a guide to the river's stage, and it is most useful when read with the page's description of impacts. A homeowner should read what the page says major flooding means at that level, and then consider the lowest level of their own building in that light.
How do forecast crests and observed crests differ?
A forecast crest is a prediction made before the water rises, and an observed crest is the height the water actually reached. A forecast may be revised, and an observed figure is the one that stands as the record for that event.
Forecasts are useful for planning, because they show the level the river may reach and the time it may get there. They are also uncertain. Rainfall, the condition of the ground and the flow upstream can all change a forecast before the crest arrives. A forecast should be read as a range of possibilities rather than a fixed height.
An observed crest is the record of what happened. Once the water has passed, the gauge's peak reading becomes the figure for that event. A reader should check whether a figure in a news report or an alert is a forecast or an observed height, because the two answer different questions.
Why must a 1913 figure be checked before it is compared with today's gauge?
The 1913 crest was recorded on the gauge then in use. If the zero point or the gauge location has since changed, its figure is not directly comparable with a current reading. The table lists the four kinds of figure a reader is likely to meet, and how to use each.
The Midwest Regional Climate Center gives the 1913 crest as 22.1 feet on the gauge then in use, and as 23.6 feet at the Anderson Waterworks site. Those figures describe the same water from two reference points. A reader who places 22.1 feet beside a current NOAA reading without checking the zero point may draw a false conclusion about how the two floods compare.
The safe course is to take each figure with its reference and its date, and to compare like with like. The table below sets out the four kinds of figure, what each describes and how to use it, so a reader can see where each one belongs.
| Figure | What it describes | How to use it |
|---|---|---|
| Gauge reading | Water height at one gauge's zero reference, at one time | Compare only with other readings from the same gauge |
| Flood stage | A threshold on the gauge where a defined effect begins | Read against the gauge's own published description of impacts |
| Historical crest | The peak of a past flood, on the gauge then in use | Check the zero point and the gauge before comparing with today |
| Forecast | A predicted crest for a future date | Treat as a prediction with uncertainty, not as a record |
How can gauge reports help a homeowner plan?
Gauge reports help a homeowner plan by showing when the river is rising and how close it is to a threshold of concern. A homeowner who knows the stage at which the lowest level of the house may be affected can act before the water arrives.
The most useful thing a gauge report does is give time. A rising reading on a published page can show that the river is climbing toward a level of concern, and that is the moment to move valuables from the lowest floor, check the sump and clear the window wells. Waiting until water is in the house leaves fewer options.
A homeowner should not rely on a single reading. The river can rise and fall, and a report that is reviewed daily shows the trend. Keep the page or the alert in a place that is easy to reach, and decide in advance what action each stage will prompt.
What does a stage threshold not tell you?
A stage threshold does not say what water will do inside a particular building. It does not measure the seepage through a wall, the flow through a window well or the water that rises from the ground. Those depend on the building and the soil around it.
A river at a given stage can still leave a basement dry if the building is high, the entries are sealed and the soil drains well. The same stage can flood a lower level that sits below the ground outside, or that has a window well or a door at a low point. The stage tells you about the river; the building tells you about the house.
This is why a reader should pair the gauge report with an inspection of the building. Walk the lowest level, note the entries, check the sump and the drains, and mark the water lines. Those observations turn a river figure into a plan for a specific house.
Where should a reader check the river level?
Check NOAA's water site for the gauge page, which is published by the National Oceanic and Atmospheric Administration. Local emergency management alerts add context about impacts and road closures, and they should be read alongside the gauge rather than instead of it.
NOAA publishes river gauge pages through its water site. The page for the Raible Avenue gauge in Anderson is the source for the 18-foot major flooding figure in this guide. Use the page directly, because it shows the current reading and the published thresholds, and check the date on any figure you are given.
Local emergency management alerts can describe the impacts the county expects at a given stage. The May 2017 alert, discussed in a separate guide on this site, is an example. Read those alerts for what they say the water will do, and read the gauge for what the river is doing.
What should a homeowner do when the river reaches a warning level?
Move valuables off the lowest floor, check the sump and its power, clear the window wells and the drains, photograph the lowest room and keep the number for the 24/7 line where it can be found. Do these before the water arrives, not after.
Start with the things that cannot be replaced. Move documents, photographs, medicines and electronics from the lowest floor to a higher level, and label them so they can be found later. Photograph the lowest room, the water marks and the stored items, so the state of the room before the water is on record.
Then check the building. Confirm the sump runs, that its discharge line is clear and that the power to it is safe. Clear the window wells of leaves and debris from outside, without standing in water. Locate the main water shut-off and the electrical panel. Those actions take little time and make the first hours after water arrives much easier to manage.
Frequently asked questions
What is the flood stage at Anderson?
NOAA's gauge page for the White River at Anderson, at the Raible Avenue gauge, lists major flooding at 18 feet. Check the page directly for the current thresholds, because the published description of impacts is the part that matters for a homeowner.
Is the 1913 record the same as the NOAA figure?
Not without a check. The 1913 crest was recorded on the gauge then in use, and the climate center gives it in two forms with different reference points. Check the zero point and the gauge before placing the figures side by side.
Does a flood stage tell me how much water will come into my basement?
No. A stage is a threshold on the river gauge. Water entering a basement depends on the building, its entries and the ground around it. A walk through the lowest level is the way to judge what a given stage could mean for your house.
Why does the gauge read differently from the water near my house?
The gauge measures the water surface at its own location. Water a short distance away can stand at a different height because of the channel, the banks and the flow. Treat the gauge as a regional reference and check the water at your house directly.
How often should I check the river level during a rise?
Check it often enough to see the trend, which can mean several times a day when the river is rising quickly. A single reading does not show whether the water is still climbing. Decide in advance which stage will prompt which action.
Who do I call once the water has reached the house?
Phones are answered 24/7. Tell the operator where the water is, how deep it is and whether it is still rising. A crew is sent as soon as one is free, and the first visit sets the plan from the water as it is found.
Sources
This guide is general information for Madison County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.