|Dredging in the Code River, Yogyakarta|
Photo from here.
The lahars flow down the channel of the Code River, which flows through the center of Yogyakarta. The river has been channelized to control the path of the lahars, a historic danger from Merapi. Sandbags up to 1 meter high help control the flows, but authorities have warned residents that these temporary levees will not contain the large flows that are likely to occur. Surono, the head of the Volcanology and Geological Disaster Mitigation Agency (PVMBG) has warned that people should stay 300 meters away from the river. Evacuation has been hindered by damage to roads and bridges, as well as by heavy traffic from people coming in to see the disaster.
An interesting side-bar mentioned in the DredgingToday.com article linked in the figure caption is that the dredging of the Code River has been hampered by the lack of heavy machinery. However, people living near the river have been helping by manually carting material away. Apparently it is well known that the volcanic mud is rich in nutrients, and a truck of this material is fetching 50-60 thousand Rp! (50,000 rupiahs convert to about $5.50 US.)