“What does “action stage” mean?” asked Christy Yates on facebook about Paddling in the treetops 2023-02-13 and for real two years ago 2021-02-27 2023-02-13.

This is relevant to the upcoming Fourth Annual Mayor and Chairman’s Paddle, Withlacoochee River 2023-03-04.

I answered: Basically, watch out, the river is high. More formally: “Action Stage – the stage which, when reached by a rising stream, represents the level where the NWS or a partner/user needs to take some type of mitigation action in preparation for possible significant hydrologic activity. The type of action taken varies for each gage location. Gage data should be closely monitored by any affected people if the stage is above action stage.

Stages, US 84 Gauge, Treetop paddling

See below for National Weather Service (NWS) terminology, which also defines several stages of flooding: minor, moderate, and major. That definitions web page is from Alaska, and it includes something called “bankfull stage” that I’ve never seen used around here. The rest of it is the same as in the Suwannee River Basin.

Right now paddling the Withlacooche River would be up in the branches like this picture, but higher. Don’t worry: the water level will probably go back down before March 4th.

Those branches are usually 20 feet overhead, 2021-02-27, 09:07:58, 30.8505670, -83.3483760

Most of our other rivers are also high like that.

Here’s what stages of the the Suwannee River Basin gauges look like today:

River Observations 2023-02-16; NWS Southeast Region River Observations zoomed to Suwannee River Basin.

Three are showing Minor Flooding today: the Skipper Bridge, Valdosta (US 41), and Quitman (US 84) gauges on the Withlacoochee River.

Four are showing Near Flood Stage, which apparently is the same as Action Stage: the Hahira, GA (GA 122) Little River gauge, the Pinetta, FL (CR 150) Withlacoochee River Gauge, and the Statenville, GA, and Jennings, FL, Alapaha River gauges.

Then, barely visible, the Ichetucknee River gauge actually shows low water. I wonder if it’s broken.

Some NWS gauges also have forecasts.

River Forecasts 2023-02-16; NWS Southeast Region River Forecasts zoomed to Suwannee River Basin

Let’s look at the forecast gauges.

The Hahira gauge is the one upstream of the March 4th paddle put in, Troupville Boat Ramp on the WWALS Withlacoochee and Little River Water Trail.

NWS thinks the Hahira gauge has peaked and is starting to go down, predicting below Action Stage by Sunday.

Hahira Gauge, Folsom Bridge, Little River @ GA 122, 2023-02-16

And here are the specific stage definitions for the Hahira Gauge:

Stages, Hahira Gauge, Little River @ GA 122, 2023-02-16

Upstream on the Withlacoochee River, the Skipper Bridge Road gauge forecast says the peak happened Tuesday, below Minor Flood by tomorrow, and below Action Stage by Monday.

Skipper Bridge Gauge, Withlacoochee River, 2023-02-16 at the site of old Skipper Bridge.

Here are the Skipper Bridge stages:

Stages, Skipper Bridge Gauge, Withlacoochee River, 2023-02-16

For the Mayor and Chairman’s Paddle, we usually also look at the US 84 gauge. The NWS prediction there says the peak will come tomorrow, back below Minor Flood by Sunday, and they don’t know when it will get below Action Stage.

Quitman Gauge, Withlacoochee River @ US 84, 2023-02-16, Hydrograph.

And the Quitman Gauge stages:

Stages, Quitman Gauge, Withlacoochee River @ US 84, 2023-02-16

There’s one Florida Withlacoochee River gauge with a forecast. The Pinetta Gauge predicts water still rising through Sunday, starting down on Monday, in Action Stage the whole time. This is normal, as the upstream water gets downstream.

Pinetta Gauge, Withlacoochee River @ CR 150, 2023-02-16, hydrograph.

It’s at Sullivan Launch on the WLRWT:

Stages, Pinetta Gauge, Withlacoochee River @ CR 150, 2023-02-16

Now let’s look at the Alapaha River, on the WWALS Alapaha River Water Trail (ARWT).

The Statenville Gauge forecast says it’s already peaked, will go down until Sunday, then start back up with predicted rains.

Statenville Gauge, Alapaha River @ GA 94, 2023-02-16

That’s just west of Statenville, GA, at the GA 94 bridge just downstream from Statenville Boat Ramp.

Stages, Statenville Gauge, Alapaha River @ GA 94, 2023-02-16

And across the GA-FL line, the Jennings Gauge seems to have had some technical difficulties, but it shows the water level peaked Tuesday, and has been between below Minor Flood but still in Action Stage since then.

Jennings Gauge, Alapaha River @ CR 150, 2023-02-16, on NWS.

That’s on CR 150 just downstream from Sasser Landing on the ARWT.

Stages, Jennings Gauge, Alapaha River @ CR 150, 2023-02-16

Finally, on the Santa Fe River, the Three Rivers Estates Gauge predicts Action Stage tomorrow, approaching Minor Flood by Tuesday.

TREPO Gauge, Santa Fe River above Ichetucknee River, 2023-02-16, on NWS.

Here are its stages. It’s on the Santa Fe River about 200 feet upstream of the Ichetucknee River Confluence, in Gilchrist County, Florida. See the WWALS map of the Suwannee River Water Trail (SRWT).

Stages, TREPO Gauge, Santa Fe River above Ichetucknee River, 2023-02-16

The TREPO gauge also has an inundation map, which is useful to see how high the water has gotten where.

Inundation Map, TREPO Gauge, Santa Fe River above Ichetucknee River, 2023-02-16, on NWS

You can also manually set the level on the map to see where the flood may get.

Valdosta and Lowndes County spend some money for LiDAR, which they used in a Flood Inundation Mapper (FIM). You can set the levels on that one, too. Here’s what FIM looks like at about the current water level on the Skipper Bridge Gauge, which is the gauge it uses:

15.7feet, Flood Inundation Mapper, Skipper Bridge Gauge

As you can see, the Langdale Park entry road appears to be underwater. I just checked with VLPRA, and indeed Langdale Park is closed.

Finally, I did not know about this one until this morning, the Tallahassee Democrat has a map that shows gauges with unusual water levels, plus shadings for river stretches with unusual levels.

Real-Time River Water Level Observation –Tallhassee Democrat 2023-02-16

It currently shows the Withlacoochee River from above Skipper Bridge Road to the GA-FL line as unusual, but “No Flooding”. In addition to Real-Time, you can set 1, 2, and 3 day forecasts.

See below for the rest of the NWS stage definitions.

And don’t forget to get your ticket for the Fourth Annual Mayor and Chairman’s Paddle, Withlacoochee River 2023-03-04.

 -jsq, John S. Quarterman, Suwannee RIVERKEEPER®

You can join this fun and work by becoming a WWALS member today!
https://wwals.net/donations/

NWS High Water Level Terminology

 

The purpose of this document is to explain the terminology used by the National Weather Service related to high water levels on streams and lakes in Alaska. There are uncountable numbers of streams and lakes of various sizes in Alaska and only a very small fraction of these have gages that monitor the water levels. Gages are devices that allow for the manual or automated monitoring of water level. The term used for the water level of a stream or lake at a gage is stage.

Stage – the level of the water surface of a river or stream above an established gage datum at a given location. The gage datum is a horizontal surface used as a zero point for measurement of water level. This gage datum level usually is located slightly below the lowest point of the stream bottom such that the stage is greater than the maximum depth of water.

Since gages are sparse in Alaska, the stage measured at each gage is used as an index of water level characteristics upstream and downstream of the gage in addition to the status at the gage. In many cases, there is only one gage on a stream system and thus the gage represents the water level characteristics in the entire stream basin. The gage is also often used to indicate the water level status of other streams or lakes in the general area that have similar characteristics to the gaged stream. People living or recreating near any stream or lake should identify the closest gage that can be used as an index for the expected water level changes at their location.

High water terms used by the National Weather Service include bankfull stage, action stage, and flood stage as defined below. In Alaska, the sparse gage network requires that these terms be defined with a broader definition that reflects characteristics of the gaged waterbody and well as nearby waterbodies. Thus the definitions consider both the specific impacts that can be documented in the vicinity of the gage as well as the expected impacts that could result on any waterbody in the general area during an event of that magnitude. The assignment of these stages thus includes the combined assessment of specific impacts and the frequency of occurrence of the event. The concept of using the frequency of occurrence of high water events to supplement the assessment of flood stages is based on the assumption that frequently occurring water levels such as the 2-year flood (50% chance of occurring in any year) will have few impacts in comparison to the significant impacts expected during an infrequent event such as a 100-year flood (1% chance of occurring in any year). When high water stages are determined from a flood frequency analysis, the impacts listed for the applicable stages will be the recurrence interval associated with that level and a qualifier to assess the quality of the recurrence interval estimate.

Bankfull Stage – an established gage height at a given location along a river or stream, above which a rise in water surface will cause the river or stream to overflow the lowest natural stream bank somewhere in the corresponding reach. The term “lowest bank” is however, not intended to apply to an unusually low place or a break in the natural bank through which the water inundates a small area. Bankfull stages on streams with natural or manmade high banks can be defined by the predominant vegetation line on the banks. The bankfull stage on many streams is associated with the 2-year recurrence interval flood. Bankfull stage is not necessarily the same as flood stage.

Action Stage – the stage which, when reached by a rising stream, represents the level where the NWS or a partner/user needs to take some type of mitigation action in preparation for possible significant hydrologic activity. The type of action taken varies for each gage location. Gage data should be closely monitored by any affected people if the stage is above action stage.

Flood Stage – an established gage height for a given location above which a rise in water surface level begins to create a hazard to lives, property, or commerce. The issuance of flood advisories or warnings is linked to flood stage. Not necessarily the same as bankfull stage.

Flood categories are terms defined for each gage location that describe or categorize the observed or expected severity of flood impacts in the corresponding stream segment or nearby stream. The severity of flooding at a given stage is not necessarily the same at all locations along a stream due to varying channel/bank characteristics on portions of the stream. Therefore, the  stage for a given flood category is usually associated with lowest water level corresponding to the most significant flood impacts somewhere in the reach. The flood categories used in the NWS are minor, moderate, and major flooding, but all three of the flood categories do not necessarily exist for each gage location. Most commonly, gages in remote areas may not have a major flood stage assigned. Record flooding is flooding that equals or exceeds the highest stage or discharge at a given site during the period of record keeping.

Minor Flooding is defined to have minimal or no property damage, but possibly some public threat. A FLOOD ADVISORY product is issued to advise the public of flood events that are expected not to exceed the minor flood category. Examples of conditions that would be considered minor flooding include:

• water over banks and in yards
• no building flooded, but some water may be under buildings built on stilts (elevated)
• personal property in low lying areas needs to be moved or it will get wet
• water overtopping roads, but not very deep or fast flowing
• water in campgrounds or on bike paths
• inconvenience or nuisance flooding
• small part of the airstrip flooded, and aircraft can still land
• one or two homes in the lowest parts of town may be cut off or get a little water in the crawl spaces or homes themselves if they are not elevated.

In remote areas with few specific impacts, floods with 5-10 year recurrence interval would be assumed to be causing minor flooding on streams in the area.

Moderate Flooding is defined to have some inundation of structures and roads near the stream. Some evacuations of people and/or transfer of property to higher elevations may be necessary. A FLOOD WARNING should be issued if moderate flooding is expected during the event. Examples of conditions that would be considered moderate flooding include:

• several buildings flooded with minor or moderate damage
• various types of infrastructure rendered temporarily useless (i.e. fuel tanks cannot be reached due to high water, roads flooded that have no alternates, generator station  flooded)
• elders and those living in the lowest parts of the village are evacuated to higher ground
• access to the airstrip is cut off or requires a boat
• water over the road is deep enough to make driving unsafe
• gravel roads likely eroded due to current moving over them
• widespread flooding, but not deep enough to float ice chunks through town
• water deep enough to make life difficult, normal life is disrupted and some hardship is endured
• airstrip closed
• travel is most likely restricted to boats

In remote areas with few specific impacts, floods with 15-40 year recurrence interval would be assumed to be causing moderate flooding on streams in the area.

Major Flooding is defined to have extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations are necessary. A FLOOD WARNING should be issued if major flooding is expected during the event. Examples of conditions that would be considered major flooding include:

• many buildings flooded, some with substantial damage or destruction
• infrastructure destroyed or rendered useless for an extended period of time
• multiple homes are flooded or moved off foundations
• everyone in threatened area is asked to evacuate
• National Guard units assist in evacuation efforts
• erosion problems are extreme
• the airstrip, fuel tanks, and the generator station are likely flooded
• loss of transportation access, communication, power and/or fuel spills are likely
• fuel tanks may float and spill and possibly float downstream
• ice chunks floating though town that could cause structural damage
• high damage estimates and high degree of danger to residents

In remote areas with few specific impacts, floods with 50-100 year recurrence interval would be assumed to be causing major flooding on streams in the area.

 -jsq, John S. Quarterman, Suwannee RIVERKEEPER®

You can join this fun and work by becoming a WWALS member today!
https://wwals.net/donations/

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