The Hydraulic Machine of Angkor

Six-Chart Analysis Dashboard · 9th–15th Century CE
Sedimentation Rate Collapse
Sediment core data from the southwest sector of the West Baray (Day et al. 2012, PNAS) reveals an order-of-magnitude decline in detrital input during the 14th century. The collapse coincides precisely with mega-drought events documented in Vietnamese cypress tree-ring records (Buckley et al. 2010). A single anomalous flood pulse in 1393 CE is visible as a brief sediment spike before final abandonment.
16×
Decline in sedimentation rate from active management (11th c.) to post-abandonment (14th c.)
1345–1365
Mega-drought window from Vietnamese tree-ring proxy (PDSI below minus 3)
~2 m
Total core depth — anomalously thick for Angkor reservoirs (typical less than 0.5 m)
1393 CE
Major flooding event visible in sediment — catastrophic monsoon after extended drought
Angkor Hydraulic Construction Timeline
Three centuries of escalating hydraulic ambition — from the first baray at Roluos (889 CE) to the peak system complexity under Jayavarman VII (~1200 CE) — followed by over a century of climate-driven infrastructure failure. Color indicates infrastructure type.
~300 yrs
From first baray (889) to peak system (1200) — continuous hydraulic expansion
25 M m³
Total earth moved for dike construction — entirely by human labor
4 barays
Built by 7 different kings across 3 centuries of Khmer rule
1431 CE
Siamese sack of Angkor — political end to a system already in hydraulic failure
System Storage Capacity Over Time
Cumulative reservoir capacity as each baray came online — showing the exponential expansion of water management infrastructure and its decline as barays silted and failed. The East Baray's failure around 1360 CE reduced system capacity by nearly half in a single generation.
112 Mm³
Peak theoretical storage — enough to supply 1 million people for months
~53 Mm³
Capacity remaining today (West Baray only — the sole surviving reservoir)
7×
Growth factor from Phase I (Indratataka only) to Phase III (all four barays)
36.6 km²
Combined baray surface area at peak — larger than many modern cities
Annual Water Budget — Peak System (~1200 CE)
Estimated annual flows through the Angkor hydraulic system at peak operation. Three river systems fed the baray network, while the majority of outflow drained to the Tonle Sap as overflow — challenging earlier assumptions that the system was primarily an irrigation engine. Values in millions of cubic metres per year (Mm³/yr). Source: Kummu 2009, Evans et al. 2013.
1,977 Mm³
Total annual inflow to the baray system from all three rivers plus direct rainfall
1,150 Mm³
Outflow to Tonle Sap as overflow — the dominant output, not irrigation
400 Mm³
Annual irrigation allocation — supporting rice paddies across the Angkor plain
22 Mm³
Urban and ritual water consumption for the city and its temples
Baray Infrastructure Comparison
Side-by-side comparison of the four major barays across storage volume, surface area, and estimated labor investment. The West Baray represents the single greatest construction effort — 11 million cubic metres of earthwork dike fill moved without draft animals or wheeled transport.
50.5 Mm³
West Baray storage — largest single reservoir, still holds water today
11 M m³
Earthwork fill for West Baray dikes — the largest earthmoving project in Khmer history
16.4 km²
West Baray surface area — 8 km by 2.1 km, visible from space
9.2 Mm³
Total moat storage across Angkor Thom, Angkor Wat, Srah Srang, and Preah Khan
Moat and Secondary Water Bodies
Moats served dual purpose — defensive barriers and secondary reservoirs feeding temple ritual pools and gardens.
Canal Network — Flow Connections
Force-directed graph of the Angkor hydraulic network. Nodes represent major system components; edges show flow direction and relative capacity. Node size reflects storage volume or flow rate. Drag nodes to explore connections. Hover for flow data.
3 rivers
Siem Reap, Puok, and Roluos rivers all fed the system from the Kulen Hills
Bampenh
Bampenh Reach spillway acted as the master distributor for the central barays
525 Mm³
Combined irrigation delivery to the Angkor plain from East and West Baray channels
Tonle Sap
Ultimate sink for the system — overflow kept the lake seasonally elevated
Hydraulic System Network
Interactive node-link diagram of the complete Angkor water system. Nodes represent sources, rivers, control structures, barays, moats, and the Tonle Sap sink. Edge thickness encodes estimated flow volume. Filter by season to isolate wet-season intake channels from dry-season distribution. Click any node to highlight its connections. Drag nodes and scroll to zoom.
Season:
1,925
Mm³/yr total system input from Phnom Kulen headwaters
7
Hierarchical tiers from source to sink, all gravity-fed on a 0.1% slope
25,000+
Hectares of irrigated rice paddy served by the distribution network at peak capacity
3
Independent river catchments feeding the baray system (Puok, Siem Reap, Roluos)
Water Budget Flow — Full System Sankey
Annual water budget for the complete Angkor hydraulic system, from Kulen rainfall inputs through the four barays to irrigation, groundwater recharge, evaporation, and Tonle Sap return flow. Ribbon width encodes flow volume. Hover any ribbon to see source, destination, and estimated Mm³/yr.
1,925
Mm³/yr total annual input (Kulen Hills rainfall + drainage basin)
790
Mm³/yr delivered to irrigation — the agricultural backbone of a million-person city
115
Mm³/yr lost to evaporation from open baray surfaces (10th–12th century peak)
850
Mm³/yr returned to Tonle Sap via overflow and groundwater base flow