River Forecast Points Flood Stages
River Forecast Point
By definition, a river forecast point refers to a gaged location on a river for which the NWS issues forecasts. These forecasts are used in warning products which are disseminated to the public.
A River Forecast Point must have the following:
1. There is some type of gage at that location (staff, bubble, wire weight or float).2. The RFC provides forecast guidance for this site.
3. A flood stage has been established.
4. An E-19 has been completed.
It is desirable that the gage be telemetered. If the gage is read by a person, it is best if the data is called in directly to a WFO. This allows for more timely data.
Establishing a River Forecast Point:
1. A gage must already exist at that location. Regional Headquarters generally do not provide river gages. However, in some cases, Regional Headquarters will supply telemetry if requested. (See B-43 information in chapter 4).
2. SH/HFP or MIC must coordinate with the RFC to obtain forecast guidance for that point.
3. SH/HFP in coordination with local authorities must establish a flood stage at that location.
4. SH/HFP must make request to Regional Headquarters/HSD for establishing the RFP through their MIC.
5. An E-19 must be completed.If the RFC is unable to provide guidance for a point which is gaged and has a flood stage, the WFO can develop their own forecast method. This may be referred to a Local River Forecast Points (Western Region), or Headwater Point (e.g. Central Region). These points must also be approved by the appropriate HSD. The method by which the WFO intends to forecast for that point should be explained.
Once a River Forecast Point has been established, the NWS is obligated to provide forecasts for that point. If the data at that point becomes no longer available, the NWS would then issue qualitative forecasts instead of quantitative. The only way a river forecast point can be discontinued is if the community and other customers no longer need forecasts for that point. Discontinuing a river forecast point needs to be coordinated with the RFC, HSD, and all customers.
To establish or change a flood stage, the SH/HFP must:
1. Coordinate with local officials and with the appropriate agencies at the county, state and federal level to determine what the flood stage will be.
2. Notify the RFC, and the appropriate Regional Headquarters/HSD of the new flood stage in writing.
3. Update the E-19 if necessary, and send updated copies to Regional Headquarters/HSD, the RFC and OH (Hydrologic Information Center).
4. Advertise this new flood stage and it's implications to residents of the area. This can be done by working through local authorities and the media. The WCM should also be involved.
Here are some characteristics to help determine the following river stages:
Bankfull - v Water flows out of it's normal banks.
v Can happen several times a year.
v May be a minor nuisance to people in the area.
v May flood pastures but not usually cultivated fields.
Action Stage* - v Stage at which some person or agency needs to pay attention to the hydrologic situation and perform a function.
v There can be no flooding at this stage.
v Action stages are not mentioned in issued products.
v Forecasts for action stages are given directly to the action agency.
v Not applicable to all regions.
* Note: Action Stage is not be used by all Regions
Flood Stage - Unleveed reach
v Need to determine what is at risk at any given gage height.
v Can be the same as bankfull, but is most often higher than bankfull.
v If a levee is built like a dam (very secure) then the FS can be much higher than the ground outside the levee (water would have to flow over the levee to flood).
v If the levee is poorly built (not very secure), then the FS should be defined as if the levee wasn't there.