NIA Central Office – The National Irrigation Administration – Magat River Integrated Irrigation System (NIA-MARIIS) issued Dam Discharge Warning No. 3 (Rapid Increase on Dam Discharge) on December 19, 2020 (1:00 PM).
NIA-MARIIS Dam and Reservoir Division – Flood Forecasting and Warning System for Dam Operations (FFWSDO) will be opening six (6) Magat Spillway Gates at 12 meters total openings with an approximate discharge of 2,360 cubic meters per second (cms) until 5:30 PM today. This is due to the recorded rainfall upstream of 33.31 mm in 13 hours as the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) has forecast of moderate to heavy rainfall within 24 hours.
| Rad. Gate No. | Gate Opening | Total Gate Opening | Time of Opening | Approx. Total Discharge | Remarks |
| RG No. 4 | Still two meters | 2 meters | 0933H | ||
| RG No. 3 | Still two meters | 4 meters | 1330H | ||
| RG No. 5 | Still two meters | 6 meters | 1430H | ||
| RG No. 6 | One meter | 7 meters | 1500H | 1,455 cms | Additional RG |
| RG No. 6 | One to two meters | 8 meters | 1530H | 1,636 cms | Increase Opening |
| RG No. 7 | One meter | 9 meters | 1600H | 1,797 cms | Additional RG |
| RG No. 7 | One to two meters | 10 meters | 1630H | 2,012 cms | Increase Opening |
| RG No. 1 | One meter | 11 meters | 1700H | 2,179 cms | Additional RG |
| RG No. 1 | One to two meters | 12 meters | 5:30H | 2,360 cms | Increase Opening |
Spillway Gate No. 5 will have additional one-meter opening at 2:30 PM, in addition to Spillway Gate No. 4 with two (2) meters, Spillway Gate No. 3 with two (2) meters, and Spillway Gate No. 5 with one-meter opening today. The approximate total discharge of six (6) meters is equivalent to 1,236 cms.
On the other hand, Spillway Gate No. 6 will have additional one-meter opening at 3:30 PM, in addition to Spillway Gate No. 4 with two (2) meters, Spillway Gate No. 3 with two (2) meters, and Spillway Gate No. 5 with two-meter opening today. The approximate total discharge of seven (7) meters is equivalent to 1,455cms.
As of 2:00 PM today, Magat Dam has a Reservoir Water Level of 191.84 meters above sea level (masl) against its Spilling Level of 193.00 masl, Inflow of 1,610 cms, Outflow of 1,148 cms, and Rule Curve Elevation of 192.62 masl. Spillway Discharge is 360 cms with two (2) gate openings with a Total Gate Opening of 4.0 meters.
NIA-MARIIS warned residents to ensure the safety of life and properties of people residing near the Magat River. (EDEN VICTORIA C. SELVA, Acting Department Manager, NIA Public Affairs and Information Staff)
