In Reply Refer To:
Mail Stop 415
December 20, 2013
OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM 2014.03
SUBJECT: Adoption and Display of Gage Operational Limits
This memo establishes and defines the term "Gage Operational Limits" (GOLs) and provides requirements for inputting the relevant threshold data in ADAPS. It describes the importance of GOLs, how they can be determined, and which data should be entered into ADAPS.
This new policy is an enhancement of the quality assurance measures introduced and required by Water Resources Division (WRD) Memorandum No. 99.34 (/admin/memo/policy/wrdpolicy99.34.html). WRD Memo No. 99.34 set forth the guidelines for establishing very-high (VHI), very-low (VLO), very-rapid-increase, and very-rapid-decrease thresholds in ADAPS to allow automatic masking from web display of potentially erroneous data and is intended to apply to all Water Mission Area (WMA) data provided on a real time basis.
Policy memo 99.34 remains in place, but this Office of Surface Water (OSW) policy provides additional guidance related to the use and determination of VHI and VLO thresholds and applies only to streamgages where real-time stage data are collected and publically displayed (NWISWeb Access codes 0 and 1). It also can be applied optionally to other sites where GOLs may exist and need to be shared or referenced. This policy requires that each Water Science Center (WSC) determine and enter appropriate streamgage operational limits so that the GOLs will appear on all public NWISWeb stage hydrographs. In addition, WSCs are encouraged to establish an appropriate “include” value in nw_edit so the threshold appears on the NWISWeb hydrograph with reasonable lead time before the upper and lower GOLs take effect.
In order to safely use and rely on USGS data, user agencies and the general public must be provided information on the physical limitations of some streamgage operations and instruments. In particular, it is important for forecasters and emergency and water managers to know the approximate stage where streamflow and water-level data will no longer be valid or available as a result of the stage sensing system reaching its minimum or maximum operational limit. This information can be provided on stage hydrographs if it is included in ADAPS screening thresholds.
The GOL is the stage at which the stage data can no longer be considered reliable. Only the WSCs can determine appropriate GOLs. Appropriate limits might include the elevations of instrument shelves and intakes, pressure transducer ranges, or other physical features or instrument limitations. Such information may be obtained by reviewing individual station descriptions or running surveys or tape downs to obtain the needed information.
To ensure a common nationwide definition of GOLs and allow their use across multiple internal and external systems, definitions for the lower and upper GOLs are provided in this memorandum. The values associated with these defined conditions must be entered as the VLO and VHI thresholds in ADAPs associated with the appropriate Data Descriptor for gage height for each streamgage where stage data are collected. An automated process in nw_edit retrieves the VLO and VHI threshold values for each streamgage, creates appropriate "Operational limits" records in the reference-levels file and a standard nationwide message for each GOL for display on NWISWeb, and will deliver the data to SIMS for station-description updating as well as to external partners such as the National Weather Service River Forecast Centers and the U.S. Army Corps of Engineers District offices.
A GOL display system has already been established in NWISWeb and NWIS to include current VLO and VHI thresholds as the minimum and maximum operating limits on NWISWeb hydrographs for internal access only. NWISWeb is configured so that limits are displayed only when data values are close to the GOLs using locked default "include" values of 90 percent for the upper GOL and +0.2 feet for the lower GOL. In many cases, the current VLO or VHI thresholds may not be the GOL, so a provision has been made so that the limits will not be displayed to the public until verified by WSCs. The addition of the character string, (POL), including the parentheses, in the ADAPS threshold remarks field will signal to the automated process that the threshold has been confirmed by the WSC as a valid operating limit and should be made available for public display. WSCs are strongly encouraged to add a comment in the remarks field for future reference that describes the situation that creates the operating limit (e.g. float limit-bottom of shelf/floor, transducer limit, lower intake invert, orifice elevation, radar sensor limit, etc.).
As a result of this policy, the following additions or modifications to ADAPS are required no later than March 1, 2014, but should be completed as soon as possible:
Very Low (VLO) threshold€”Enter the gage height value that corresponds to the lower limit of reliable gage height data. Add the character string, (POL), including the parentheses, in the ADAPS threshold remarks field. This string signals approval for displaying the VLO to the public on NWISWeb. Add additional information in the remarks field to describe the situation that results in the lower limit and the date of last inspection. Determine the appropriate "include"; value for the lower GOL and change the default value of +0.2 feet, if necessary, by adding the character string "include_at(xx.x)", without the quotes, in the threshold remarks field. When the recorded gage height reaches xx.x ft, the threshold line will appear on the NWISWeb hydrograph and it will be removed when the gage height rises above xx.x ft.
Very High (VHI) threshold€”Enter the gage height value that corresponds to the upper limit of reliable gage height data collection or transmission. In some cases, the upper gage operating limit may be the inability to transmit data due to a Data Collection Platform (DCP) failure rather than the ability to collect reliable data. Add the character string, (POL), including the parentheses, in the ADAPS threshold remarks field. This string signals WSC approval for displaying the VHI to the public on NWISWeb. Add additional information in the remarks field to identify the reason for the upper limit reason and the date of last inspection. Determine the appropriate "include" value for the upper GOL and change the default value of 90 percent in nw_edit, if necessary, by adding the character string "include_at(xx.x)", without the quotes, in the threshold remarks field. When the recorded gage height reaches xx.x ft, the threshold line will appear on the NWISWeb hydrograph and it will be removed when the gage height falls below xx.x ft.
WSCs are reminded that the OSW Script "thresh.scan" will provide a list of current threshold settings in ADAPS for NWISWeb publically displayed data descriptors. WSCs can use this script to easily create a list of current settings as they evaluate what revised settings are appropriate and what settings may need further scrutiny.
If there is sufficient interest, OSW will provide a webinar to discuss the development and inputting of GOLs.
The completion of this task for all streamgages operated by your WSC where stage data are collected will ensure the public display of GOLs. As a result, we are asking that WSCs assign this task as a priority during their year-end 2013 hydrologic records review and make these data available as early as possible in the 2014 water year and no later than March 1, 2014.
Robert R. Mason, Jr.
Deputy Chief, Office of Surface Water
Distribution: GS-W All