| Opak River Sungai Opak, Kali Opak | |
|---|---|
 Opak River as viewed from Jetis, Bantul | |
  Location of river mouth Show map of Java Opak River (Indonesia) Show map of Indonesia | |
| Location | |
| Country | Indonesia |
| State | Yogyakarta |
| Region | Bantul Regency,Sleman Regency |
| Physical characteristics | |
| Source | Mount Merapi |
| Mouth | |
• location | Indian Ocean |
| Length | 65 km (40 mi) |
| Basin size | 638.89 km2 (246.68 sq mi) |
Opak River is a river in central south area ofJava island, Indonesia.[1]
It flows from its source on the slopes ofMount Merapi in the north, heading southward and passes the west side of 9th-centuryPrambanan temple compound, located to the east ofYogyakarta and southeast ofKota Gede.
It also passes the historical locations ofPlered,Karta, andImogiri before draining into theIndian Ocean in the southern part ofBantul.
The river runs upon Opak tectonic fault, a major tectonic fault in southern Central Java responsible for major earthquakes in the region..
The river basin that it lies in is significant as the aquifer is in a heavily populated part of Java[2] One of the tributaries isOyo River.
The river flows in the southwest area of Java with predominantlytropical monsoon climate (designated asAm in the Köppen-Geiger climate classification).[3] The annual average temperature in the area is 22 °C. The warmest month is October, when the average temperature is around 26 °C, and the coldest is January, at 18 °C.[4] The average annual rainfall is 2970 mm. The wettest month is January, with an average of 537 mm rainfall, and the driest is September, with 22 mm rainfall.[5]
