We calculated the daily discharge rate of water in cubic meters per second entering Falling Creek Reservoir through the gauged weir on its primary inflow. This weir was rectangular from 15 May 2013 to 6 June 2019, when it was replaced by a V-notched weir (7 June 2019 to present). Inflow was calculated from a pressure sensor installed at the weir by the Western Virginia Water Authority (WVWA) from 15 May 2013 to 31 December 2022 and a pressure sensor installed by Virginia Tech (VT) researchers (PI Cayelan Carey) from 22 April 2019 to December 2022. Collection of both datasets is ongoing.
We measured the amount of water entering into the reservoir through the weir with an INW Aquistar PT2X pressure sensor (INW, Kirkland, Washington, USA) installed by the WVWA, which recorded the weir water level with a pressure sensor and stream temperature every 15 minutes. From 22 April 2019 to December 2022, we also measured pressure and stream temperature every 15 minutes using a Campbell Scientific CS451 (Campbell Scientific, Logan, Utah, USA; SN: 5318) pressure transducer installed by VT. As noted above, from 15 May 2013 - 6 June 2019, a rectangular weir was installed; from 7 June 2019 to 31 Dec 2022, a v-notch weir was installed. The water level data were used to calculate the daily flow rate of water entering into the reservoir, following Gerling et al. (2014) for the rectangular weir (15 May 2013 - 6 June 2019) and the equation below for the v-notch weir (7 June 2019 - December 2022):
V-notch weir, discharge equation:
Q = 2.391 x H^2.5
Where Q is the calculated discharge (m^3 s^-1), 2.391 is the conversion factor for a 120 degree angle -notch weir in m^3 s^-1, and H is the head on the weir (m). We note that for the VT sensor, there was no rating curve developed for the rectangular weir (22 Apr 2019 to 6 Jun 2019) and discharge could not be calculated but pressure and temperature are still reported for this time interval.
A rating curve was developed using correlations between gauge height and pressure measured for each of the installed pressure sensors (WVWA and VT) from 10 June 2019 to 6 Jul 2020 (included as a supplementary dataset, FCR_Inflow_GaugeHeight_2013_2022.csv). Briefly, the weir level (cm) was intermittently recorded throughout 10 June 2019 to 6 Jul 2020. The date and time stamp from each measurement was used to identify the closest pressure reading for both the WVWA and VT pressure sensors. A separate rating curve was developed for the WVWA (gauge height = 63.163 x pressure - 8.7014) and VT (gauge height = 70.640 x pressure - 5.6633) data to convert pressure to gage height (cm) from 6 June 2019 to 24 Aug 2020. Gauge height was then converted to (m) and used to calculate discharge as described above.
On 20 Jul 2020, there was a rapid drop in pressure measured at the weir. On 10 Aug 2020, field crew personnel noted the weir had been breached. Thus, both pressure sensors (WVWA and VT) were removed from the weir on 13 Aug 2020 and were re-installed on 24 Aug 2020 after the weir had been fixed.
A rating curve was developed for the time period from 24 Aug 2020 to 02 Sep 2020 for both the WVWA (gauge height = 53.191 x pressure - 1.0851) and VT (gauge height = 58.140 x pressure + 2.9302) sensors. On 02 Sep 2020, the pressure transducers (WVWA and VT) were moved again to prevent sediment burial. Therefore, a third rating curve was developed from 02 Sep 2020 to 08 Nov 2021 for both the WVWA (gauge height = 69.021 x pressure + 0.812) and VT (gauge height = 71.993 x pressure + 5.801) sensors when batteries in the WVWA pressure sensor were replaced. Another rating curve was developed from 08 Nov 2021 to 09 May 2022 when the weir was dredged WVWA (gauge height = 84.52082 x pressure -6.381252) and VT (gauge height = 84.86239 x pressure + 1.719037). Subsequent rating curves were made for VT sensor from 09 May 2022 to 16 Nov 2022 VT (gauge height = 71.6103 x pressure + 2.412859) and 16 Nov 2022 to 31 Dec 2022 (gauge height = 71.42857 x pressure + 1.5). For the WVWA senor a rating curve was developed from 09 May 2022 to 31 Dec 2022 (gauge height = 72.51036 x pressure -5.226). The rating curve is calculated in the Inflow_QAQC _2013_2022.R script and the time period for each rating curve is in the FCR_Inflow_Maintenance_RatingCurveLog_2013_2022.csv under RATING. As new observations from the gauge height (see FCR_Inflow_GaugeHeight_2013_2022.csv) are added the current rating curve will be updated each year.
From 08 Nov 2021 to 16 Nov 2022 the VT sensor was about 2.3 cm higher than the WVWA senor which resulted in lower estimated flow. We converted cm to psi using the relationship 1psi = 2.31 ft. from the Campbell Scientific CS451 Manual. So, we added 0.033 psi to all observations from the VT_Pressure_psia observations and flagged with a 1 for- value corrected to account for artificial increase in pressure after sensor maintenance.
All other maintenance issues can be found in the FCR_Inflow_Maintenance_RatingCurveLog_2013_2022.csv.
### Data Flags
For the 15 May 2013 - 6 June 2019, the weir installed at the inflow was rectangular, and thus very low flows were often not well-resolved by our flow equation. At these times, flow is reported as NA. However, the Falling Creek Reservoir inflow stream generally does have perennial flow.
For 6 June 2019 - present, flow over-topped the weir at 27.5 cm (WVWA pressure = 0.573, 0.5374, 0.387, 0.401, 0.451; VT pressure = 0.469, 0.423, 0.301, 0.304, 0.350, 0.364, for the rating curves, respectively). Flow observations which over-topped the weir were retained but flagged in the data set. Flow was below the weir at 0 cm (WVWA pressure = 0.138, 0.020, -0.012, 0.075, 0.072; VT pressure = 0.082, -0.054, -0.086, -0.020, -0.033, -0.021 for the rating curves, respectively). Flows below these pressures for the time period from 6 June 2019 - present were set to NA and flagged. We note that measurements with multiple flags are coded as a multiple-digit number (e.g., a flag of '12' indicates there was 1 = value down-corrected to account for artificial increase in pressure after sensor maintenance and 2 = sensor malfunction). No delimiter was added to separate flag codes in those columns.
We added data flags for missing data and when sensors were removed for maintenance, 7 and 8 respectively.
### Notes
For data published as part of previous datasets (EDI identifier 202.9), we note several changes to the previous version (202.8). First, WVWA sensor observations have been given the correct time stamp. In previous datasets all observations were assumed to be in EST when in fact the time zone was based on when the original data file had begun. Because of this some of the rating curves for the WVWA sensors have changed slightly.
This year we also added a section to calculate the rating curves automatically in the script so when new observations are added to the FCR_Inflow_GaugeHeight_2013_2022.csv the rating curve will be updated. The script outputs the slope and intercept, along with low observations and high observations for each rating curve. The outputs are updated the methods section each year.
The Maintenance log as well as rating curve time periods are published with the data set so it is easier to find the dates and times of both sensor issues and when the sensors were moved and rating curves started and ended.
Please note: When pulling the file via EDI's API, we recommend using the function "read.csv" instead of "read_csv". The function 'read_csv' identifies the columns for the VT data and associated flags as "logical" instead of "double" due to >100 NA's at the beginning of the dataset. This is avoided when using the function "read.csv".
### References:
Gerling, A. B., R. G. Browne, P. A. Gantzer, M. H. Mobley, J. C. Little, and C. C. Carey. 2014. First report of the successful operation of a side stream supersaturation hypolimnetic oxygenation system in a eutrophic, shallow reservoir. Water Research 67: 129-143. DOI: 10.1016/j.watres.2014.09.002
014.09.002
