PJT assures Wonorejo Reservoir services normal despite water level decline
Perum Jasa Tirta I Wonorejo, as the operator of Wonorejo Reservoir in Tulungagung, has assured that agricultural irrigation services and hydroelectric power plant (PLTA) operations are still running normally despite the reservoir water level falling to 5.7 metres below the operational pattern due to minimal inflow during the dry season.
PJT I Wonorejo Supervisor Edi Mustamar said on Friday that the reservoir water level on Thursday (27/8/2029) was recorded at 165.67 metres SHVP (Surabaya Haven Vloed Peil), whereas under the operational pattern it should have been around 171.3 metres.
“Reservoir operations are indeed below the pattern, but so far it remains sufficiently safe to serve irrigation needs and PLTA operations,” he said.
According to Edi, the water level decline occurred because nearly all rivers originating in the Wilis Mountains and flowing into Wonorejo Reservoir have begun experiencing reduced discharge, with some having stopped flowing entirely during the dry season.
On the other hand, the reservoir must continue releasing water to meet agricultural irrigation needs and support PLTA operations, which are currently run for five hours during peak load periods, from 5.00 p.m. to 10.00 p.m. Western Indonesia Time.
He explained that the average reservoir water level decline currently reaches about seven centimetres per day. Nevertheless, the condition remains within safe limits based on operational simulations through to the end of the year.
The reservoir operator estimates that if no rain falls until the end of October 2026, the water level will still be around 158.45 metres. That figure remains above the minimum PLTA operational threshold of 153 metres.
“Even under the worst-case scenario of the dry season lasting until the end of December, the water level is still estimated to be above 157 metres, so reservoir operations remain safe,” he said.
Management data shows the lowest level ever recorded at Wonorejo Reservoir occurred in 2017 at around 158 metres. To date, the reservoir condition remains above that figure.
Wonorejo Reservoir is currently releasing about 902,000 cubic metres of water per day to meet public service needs, particularly agricultural irrigation, which is the dam’s primary function.
The operator hopes rain will begin falling at the start of the rainy season so that inflows increase again and the reservoir level can recover gradually to maintain the sustainability of water supply for the agricultural and energy sectors in Tulungagung and surrounding areas.