The Magat Dam Protocol on Dam Discharge and Flood Warning Operation

The Magat Dam Protocol on Dam Discharge and Flood Warning Operation


I. Before the Coming of Typhoon

      1. Coordinatinate with PAGASA
                a. Know the expected date and time of landfall of the typhoon, speed and direction
                b. Intensity of rainfall.
                c. Any disturbance aside from tropical cyclone.
       2. Warning Steps
                a. Manual inspection / check up warning stations and equipment.
                b. Six (6) hours before pre – release, activate the warning stations.
       3. Drawdown the Magat Reservoir Water Level 2-3 days before the expected landfall of the typhoon.
                a. Inform concern Agencies such as OCD, LGU’s, PNP, MEDIA and NGO’s.
 

II. During the Typhoon

        1. Dam Discharge and Flood Operation
                a. Inflow forecasting - Base on the amount of telemetered rainfall observed and recorded.
                b. Warning on intensive rainfall issued by PAGASA - Inflow is increasing and exceeds 1,600 cu.m/sec.
                    (Note : 1,600 cu.m/sec inflow is considered start of flood.)
                c. Issuance and dissemination of the dam discharge warning to the public.
                       -Thru the warning stations.
                       -Thru commercial radio stations and local TV network.
                       -Thru other means (SMS, fax, radio) to all agencies concern.
                       -Regulation of outflow from the Dam to mitigate flood damage to the downstream.
               d. Release of flood water in the reservoir.

 

III. After the Typhoon

              a. Regulation of outflow from the Dam to mitigate flood damage to the downstream.
              b. Termination of Dam Discharge Warning.
              c. Filling the reservoir to elevation 193.00m by the end of the flood.

 

Rerservoir Operating Rule Curve

The reservoir is presently operated in accordance with an Operation Rule Curve jointly developed by the NIA, NAPOCOR and NWRB in 1985 to optimize the utilization of the water stored in the Magat reservoir. It sets the minimum month-end reservoir elevations that shall be maintained by controlling reservoir releases to ensure water availability for irrigation on a year-round basis. This requires that the reservoir has to be filled up to its full supply level of elevation 193.00 at year- end. During the months of January to May which are normally dry months, water release for irrigation normally exceeds the river flow resulting to reservoir drawdown, however, during the months of June to November, river flow normally exceeds the irrigation requirement and the reservoir re-fills.

 

The criteria associated with the Operation Rule Curve are as follows:

  • Under normal condition, the reservoir elevation shall not be allowed to go below the rule curve except during the occurrence of floods where a decision to pre-release was arrived at.
  • As long as the reservoir elevation is above the rule curve, additional water releases for power generation on top of the irrigation diversion requirement (IDR) will be allowed provided that the projected month-end reservoir elevation shall not fall below the rule curve elevation based on a critical analysis by MARIIS.

 

Normal Irrigation and Power Releases

In cases where inflow exceeds the IDR, all water releases, whether for irrigation or for power or for both, shall be made to pass through the Magat and Baligatan Hydroelectric Plants whenever possible to keep or return the reservoir to the rule curve level. As a general rule, NIA-MARIIS shall provide SNAP with the weekly IDR every Friday following each week for the latter’s information and adjustment in their planning. In the event that there is a change in the IDR, NIA shall recompute the weekly IDR for the remaining weeks of the season and provide SNAP a copy of the same.

 

Spillway Releases for Irrigation

Water for irrigation is released through the spillway gates only when the Magat Hydroelectric Plant is partially or completely shut down. If the reservoir level is higher than elevation 174.00, the releases shall be made through Gates 3, 4 and 5 of the ogee spillway but if it is lower than elevation 174.00, the releases should be made through the orifice spillway.