How does it work?
The science behind the Report indicates that habitat conditions vary depending on two measurable factors: streamflow volume and the passage of time. The entire methodology and the science used for selecting the reference fish community, determining each species habitat conditions, and ultimately the setting of "optimal" streamflow thresholds and continuous days duration below thesholds is too lengthy to discuss here, but it is interesting and you are encouraged to explore it in depth by clicking on the link above.
The "Signal" of the meter on any given day will be either Green, Yellow, Red or N/A signifying either Normal, Dangerous, or Catastrophic habitat conditions on the river. An N/A indicates data was Not Available that day. The Report states that Green signals represent normal streamflow conditions. Under Yellow signals voluntary steps to conserve water should be undertaken by the Watershed community. Under Red conditions mandatory conservation measures are recommended.
The meter also displays a "Level" indicator that is, under normal operating conditions, either Blank, 1, 2 or 3. The Level is indicative of habitat conditions relative to streamflow thresholds that occur in the common course of annual cycles (Level 1), of more restrictive habitat conditions as determined by low streamflow thresholds (Level 2), or of seriously low streamflows that dramatically impact habitat (Level 3). If the Level is Blank it indicates that streamflow volume is above the highest threshold set at Level 1. In situations where the Signal indicator is N/A, the Level indicator may provide the reason for the lack of data. "Ice" indicates the streamflow guage was not providing data due to ice buildup in the river. "BPU", for Bioperiod Parameters Undefined, indicates the Mesohabsim threshold parameters are not defined for this bioperiod. In the case of the PRWC, the Spring Flood bioperiod threshold parameters, from March 1st through April 30th, were not completed in the Mesohabsim study conducted for the organization.
In combination, Red Level 2 & 3 conditons drastically diminish habitat and should not occur more often than once every decade.
Logic / Computations
Each Level has an associated days duration counter, or "clock" as the scientists like to call them, as well as three threshold parameters that vary depending on which Bioperiod for fish fauna is currently in effect: a Base Flow threshold, a Persistent Days Duration threshold and a Catastrophic Days Duration threshold. The clock keeps a tally of the number of consecutive days the USGS dishcharge flow guage has been below the Base Flow threshold for a given Level. The method by which the program calculates the days duration counter for each Event is as follows:
1) On the transition day to a new bioperiod clocks are reset to zero.
2) Each day the actual discharge flow is compared to the flow threshold in effect for the bioperiod.
3) If the flow is below the flow threshold the clock is incremented by one.
4) It takes two consecutive days of flows at or above the flow threshold to reset the clock to zero. On the first such day the clock is trimmed in half.
5) The clock is compared to the day’s duration thresholds. If it is equal to or greater than the catastrophic days duration threshold a red status is assigned to the Event. If it is equal to or greater than the persistent days duration threshold a yellow status is assigned. Any lesser value assigns a green status.
The process by which the Habitat Meter simplifies the ACTogram summary to one color-coded signal is by scanning each Level and color status for the worst-case habitat condition. The hierarchy ranking system uses the color as the primary element and the Level as the secondary element. From worst to best are: red, yellow, green and Level 3, Level 2 and Level 1 respectively.
Bioperiod transitions present a unique situation for the Habitat Meter. Since the clocks reset to zero, the Habitat Meter will continue to signal the prior bioperiods concluding days ACT color status as long as that status is worse than the current bioperiods ACT color status and the daily discharge flow remains below the flow threshold (in essence, until a "significant" precipitation event). When either of these conditions is negated the current bioperiod ACT clock and color status are activated.
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