The salutary influence

Full-length paper
Asian Agri-History Vol. 9, No. 4, 2005 (275–289) 275
The Salutary Influence of Irrigation on Human
Settlement, Economy, and Political Power in
Pre-modern Southeast Asia
Y Yagama Reddy
Centre for Studies on Indochina and South Pacific, Sri Venkateswara University, Tirupati 517 502,
Andhra Pradesh, India (email yagamareddy_asp@rediffmail.com
)
Abstract
The tropical monsoon rhythm for over centuries obviously occasioned the development
of waterworks which facilitated wet rice cultivation in pre-modern Southeast Asia.
The small-scale waterworks, purely an outcome of local initiative which survived for
many centuries and outlived the state, were developed in the dry zone of Irrawaddy
valley in the rain-shadow region of Menam Basin and on the terraced hill sites of
Champa as well as in some lowland areas and volcanic uplands of insular realm. On
the contrary, the elaborated and large-scale irrigation and water control system was
forged by the well organized society under the aegis of the state, as was accomplished
by the Khmers in the lower Mekong valley and the Vietnamese in the Red river delta.
The ingeniously built integrated canal system in Satingra peninsula (southern-most
Thailand) also deserves appreciation. All these water schemes of great antiquity, though
primitive and crude, have testified to their efficacy of serving the demands of the
peasantry and the state. These community-based waterworks, unlike the major
irrigation schemes, need to be maintained by all the Southeast Asian countries.
Although reckoned as an entity, Southeast
Asia presents vivid contrasts that subscribe to the notion of paradoxes. Quite analogous to this generalization is the regional physical character which, nonetheless, broadly constitutes a peninsula (mainland) and several thousands of islands (insular realm).
These two broad physical divisions, in their geological structure, symbolize respectively longitudinal and latitudinal mountain ranges.
Much in conformity with the trends in geological structure is the drainage pattern formed by the major rivers in Southeast Asia.
Thus, there are narrow and elongated
(longitudinal) river valleys trending in north- south direction in the mainland, in contrast to the multitude of short river courses flowing indifferent directions in the archipelagic region. The long and sustained fluvial action of erosion and deposition, in the context of tropical monsoon rhythm and recurring volcanic activity, has produced

276 Salutary influence of irrigation complex landforms – steep and rugged mountain slopes, inter-montane basins,
subdued relief features like plateaus, floodplains, deltas, and coastal lowlands. Far beyond this geological process, what is of much historical significance are the narrow,
constricted, parallel mountain chains inasmuch as they eventually formed an impenetrable barrier for the movement of goods and people to and from the Asia interior, besides imposing similar impediments on Southeast Asia.
The deeply dissected valleys had thus reduced the volume, if not the variety, of migrants from the Tibeto-Yunan plateau region (southern China) into Southeast Asia.
During the millennium-long process of southward migrations of the people of
Mongoloid stock, the limited extent of fertile lowlands, though more of an exception than a rule, evolved as the centers of political and economic activity and thereby as the clusters of population, repugnant to the expansive uplands bearing no demographic and economic significance. The productive lowlands had thus become the bone of contention between the earlier settlers and the successive waves of migrants who ultimately emerged as the dominant ethno- linguistic groups as, for example, Mons in the lower and central Burma, Burmans in the central Burma, Khmers (Cambodians)
in the lower Mekong, Thais in the Chao
Phraya (Menam) valley, and Vietnamese in the Tongking (Red river in northern Vietnam)
and Cochin-China (trans-Bassac plain in southern Vietnam. All such early states formed by these dominant ethnic groups though not necessarily located in the vicinity of great rivers of Irrawaddy, Salween, Chao
Phraya, Song Koi (Red river, and Mekong
(Stargardt, 1986) – developed on the fringes of great alluvial tracts, especially in the vicinity of irrigation works which formed the basis of centralized political authority (Cady,
1976).
The tropical monsoon rhythm, marked by the reversal of prevailing wind directions
(during May–November) and the intervening transition period (December–
April), makes Southeast Asia experience an alternation of wet and dry seasons as well as the spatial variations in the rainfall resulting in floods in some areas and drought conditions elsewhere simultaneously. Whilst the heavy rainfall (>1500 mm) is of little significance for the second crop, the lower amounts of rainfall do barely meet the needs of even a single crop. Appropriate irrigation practices have thus become an imperative need for ensuring lucrative harvesting of two or more crops in a year. This peculiar climatic rhythm, having persisted for over centuries, had played a deterministic role in the pursuit of developing waterworks by the people or the state. Obviously, the historical settlement was also very much related to the lowland rice (sawah)
cultivation although based on different primitive forms of irrigation. It was about