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 2021 and a pressure sensor installed by Virginia Tech (VT) researchers (PI Cayelan Carey) from 22 April 2019 to 31 Dec 2021. 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 31 Dec 2021, 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 2021, 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 - 31 Dec 2021):
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 gage 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 datasets). 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 (gage height = 65.501 x pressure - 9.849) and VT (gage height = 70.640 x pressure - 5.6633) data to convert pressure to gage height (cm) from 6 June 2019 to 20 Jul 2020. Gage 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 (gage height = 55.556 x pressure - 1.8333) and VT (gage 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 present for both the WVWA (gage height = 69.896 x pressure - 0.447) and VT (gage height = 70.919 x pressure + 6.114) sensors. Weir level data used for rating curve development can be found in the supplementary datasets (2020_WeirWaterLevel.csv, 2021_WeirWaterLevel.csv).
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 = 0.570, 0.528, 0.394; VT pressure = 0.469, 0.423, 0.302 for the three 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 = 0.150, 0.033, 0.006; VT pressure = 0.080, -0.050, -0.086 for the three 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.
For data published as part of previous datasets (EDI identifier 202.7), we note several changes to the previous version (202.6). First, the offset originally applied to the data set from 18 April 2016 to 09 Mar 2020 has been removed for the period from 07 Jun 2019 through 09 Mar 2020. The offset originally applied to the data was in response to changes in sensor location on 18 April 2016 and was no longer valid once the sensors had been moved during the construction of the v-notch weir on 06 Jun 2019. In addition, we removed flow data calculated from the VT pressure transducer from 22 Apr 2019 to 07 Jun 2019 (but left pressure and depth data in the dataset for this period). During this time period, we did not have a reliable rating curve for the VT pressure transducer and thus cannot accurately calculate flow.
From 14 May 2020 to 24 Aug 2020, data from the WVWA pressure transducer does not exist due to a sensor malfunction. This occurred again from 21 July 2021 to 26 Oct 2021.
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
