The river that moves house
The Ili River, originating in China's Tian Shan mountains, is the lifeblood of southeastern Kazakhstan. It provides 70-80% of the inflow to Lake Balkhash, a massive freshwater and saltwater lake in an otherwise arid landscape. Before reaching the lake, the river fans out into the vast Ili Delta, a wetland complex covering over 8,000 square kilometers. From space, this delta shows a strange and restless history. Satellite images map more than 25 distinct paleochannels—the dry, abandoned beds of former river distributaries.
This is a landscape defined by avulsion, the process where a river abruptly abandons its channel to carve a new path across its floodplain. Scientists studying the delta's geology have used radiocarbon dating on organic materials found within these old channels to establish a timeline for these shifts. The data show that the Ili Delta undergoes a major avulsion every 200 to 300 years. This process is driven by the river's own success. As it flows, it deposits immense amounts of sediment, gradually raising its channel bed until it sits higher than the surrounding terrain. Eventually, a major flood breaches the bank, and the water rushes into a new, lower-elevation path, abandoning the old channel entirely.
These ancient, dry riverbeds, known locally as "bakanas," crisscross the Saryesik-Atyrau Desert east of the modern delta. Each one represents a past version of the Ili, a snapshot of a landscape in constant, dramatic motion. The study of these features records the delta's hydrogeological evolution over millennia.
Stranded by the water
For ancient civilizations, the Ili Delta's periodic relocation was a catastrophic event. Settlements that thrived on the riverbanks, relying on its water for agriculture and trade, would find themselves suddenly stranded in an arid wasteland. The river's jump would leave entire irrigation networks useless and force the complete abandonment of cities and fields. Archaeological work in the wider Ili River Valley has uncovered numerous sites from the Bronze Age onward, showing a long history of human settlement in this dynamic region. Medieval cities like Ilanbalyk (also known as Uch-Aral), a stop on the Silk Road, were situated in the river valley and would have been profoundly affected by the availability of water.
The modern delta is not immune to change. The construction of the Kapchagay Reservoir in 1970 significantly altered the river's flow and sediment transport. The reservoir traps much of the sediment that would naturally build the delta, while also reducing the volume of water that reaches Lake Balkhash. Between 1970 and 1987, the lake's level dropped by 2.2 meters. This human intervention has slowed the natural avulsion process but introduces new threats, disrupting the ecological balance of this immense and important wetland, which is recognized as a Ramsar Site of international importance.