|Conservation and Development in Northern Thailand. Proceedings of a Programmatic Workshop on Agro-forestry and Highland-Lowland Interactive Systems, Held at Chiang Mai, Thailand, 13-17 November 1978 (UNU, 1980, 114 pages)|
|On the significance of the watershed management approach in studying highland-lowland interactive systems|
Review of current research on agriculture in the highlands of northern thailand
A watershed as a complex natural ecosystem provides one of the best means to study the behaviour of a natural ecosystem. especially from the point of view of the interaction of its key components. minimizing the fluctuating of water debit, which is most widely interrelated to the other objectives of area based development, can be used as a key indicator of the state of natural resource utilization in a given watershed. in the development process the spatial divisions are upland, lowland, and coastal subsystems. interfacial aspects between development subsystems may be described using a cross impact matrix.
There are two schools of thought in area-based research or development: (1 ) the administrative approach, and (2) the watershed approach. the only advantage in using the administrative approach (province, district, or county) lies in the fact that it is already operational it is familiar both to the planners and to the executives. however, this approach does not fit natural resource development in which the three basic components are land, water, and biological resources. in policy analysis and implementation, both approaches can be synthesized. interest in watershed analysis stems from the evidence that (1 ) water resource utilization is best optimized through basin-wide management, (2) as the water resource component is analogous to the blood systems in animal bodies, it provides the best method to diagnose the state of natural resources utilization in a given watershed, and (3) fluctuation of water debit is most widely interrelated to the other objectives of area-based development as is shown in the following compatibility matrix (see table 1).
Table 1. Compatibility matrix of objectives
|z1 water yield||1|
|z2 water debit fluctuation||-||2|
|z3 water quality||+||-||3|
|z4 erosion level||-||+||-||4|
|z5 soil fertility||+||-||+||-||5|
|z6 food production||+||-||+||-||+||6|
|z7 electric power and fuel||+||-||-||-||+||+||7|
|z8 building material||+||-||-||0||+||0/-||+||8|
|z10 industry and mining||+||-||-||-||0||+||+||+||+||10|
|z11 income equity||0||-||0||0||0||+||+||+||0||+||11|
|z17 natural beauty||0||-||+||-||+||0/-||-||-||0/+||-||0/+||0/+||0||0/+||0||0/-||17|
|z18 historical, cultural, and archaeological considerations||0||0||0||0||0||0||0||0||+||0||0/-||+||0||0||0||0||+||18|
|z19 minimum waste||+||-||+||+||+||+||+||-||0||-||0||0||0||0||0||0||+||0||19|
z2 = f (z1. z3, z4. z5, z6, z7, z8 z9 z10 z11, z12, z13. z14. 717. z19). and
z15 = n (z4, z5, z6 z7 z9 z10 711 z12. z14), and
z16 = g (74 z5 z7 z8 z9, z10 z14. z17), then
z2 (fluctuation of water debit) interrelates with other objectives except z18 (historical, cultural, and archaelogical aspects) and z20 (uniqueness). this means that z18 and z20 can be managed separately while z2 can be used as a measure of performance of watershed management. in other words fluctuation of water debit can be considered as a state variable which should be attained in each time span in the whole planning horizon (see fig. 1).
one obvious advantage of using fluctuation of water debit as an indicator is that it is easily measured. with proper management strategies, fluctuation of water debit could be minimized (or minimize dz2/dt)
the ideal condition is when dz2/dt = 0 since this kind of condition is only theoretical, our effort is to achieve a certain permissible level of fluctuation, in which dz2/dt = m. the value of m should be the target from one time span to the other time spans. using multi-criterion optimization models, z2 is the most important one to be minimized. the remaining 17 objectives are then treated as constraints in the subsequent optimization process by specifying a minimum level of attainment for each of these secondary objectives.
as a system, a watershed may be divided into three subsystems: upland, lowland, and coastal subsystems (see fig. 2). the boundary between upland and lowland subsystems is a line connecting potential sites of reservoir construction, while the boundary between lowland and coastal subsystems is a line connecting the points in which marine influences are significantly detectable, through cation distribution or electrical conductivity. the idea to divide the watershed ecosystems into those three subsystems is based on the consideration that each subsystem has its own function and characteristics:
referring to fig. 2, what is to be transferred is water. however, it can be expressed in terms of energy or nutrient flow. for each subsystem the components are vegetation, land, and channel networks.
the cross impact matrix of table 2 depicts the closed loop interactions between subsystems, in which each element of the matrix tells the effect of a row subsystem on a column subsystem. the upland subsystem supplies water regularly all year around to be used efficiently in the lowland and coastal subsystem. the lowland subsystem should be developed into efficient agriculture and industrial estates to generate employment opportunities. mangrove forest in the coastal subsystem is a protection belt against marine influences. a more detailed closed loop of interactions between variables should be scrutinized further in the form of a causal diagram loop.
FIG. 1. Decreasing Fluctuation of Water Debit over Tirne. (t = time span; T = planning horizon; Z2 = fluctuation of water debit.)
TABLE 2. Interfacial Aspects of a Watershed Development
|Change in||Upland subsystem||Lowland subsystem||Coastal subsystem|
|Upland subsystem||Irrigation networks dev More efficient use of water. Labour
intensive dev. to accommodate migrants from the upland through |
( 1 ) Agric. Intensification and diversification.
(2) Agro-based industries. and
(3) Dev. of transportation
|Lowland subsystem||Minimizing fluctuation of water debit through land treatment, vegetation cover, and management of channel systems. Selective and protective agricultural technology. To relieve population pressure on agricultural land||Dev. of mangrove forest belt to minimize salt in trusion. prevent marine erosion. as wind breaker. Spawning and nursery ground of commercially important aquatic species, supporting land accretion processes.|
|Coastal subsystem||Minimizing fluctuation of water debit through land treatment, vegetation cover and management of channel systems. Selective agric -technology. To relieve population pressure on agric land.||Irrigation networks dev. Special irrigation for brackish water ponds. Aquatic weed control. Proper use of pesticides industrial pollution abatement.|
Chow, V.T., ed. 1964 Handbook of Applied Hydrology. New York: McGraw-Hill Book Company
Knop. H, ed. 1975. Proceedings of the UNEP/IIASA Meeting of Experts on Environmental Management.
Reichle, D E 1970 Analysis of Temperate Forest Ecosystems. New York: Springer-Verlag.
Sharif. N., and P. Adulbhan. ed. 1978. Systems Models for Decision Making. Bangkok: Asian Institute of Technology
White, F.G . ed. 1977 Environmental Effects of Complex River Development. Boulder, Colo: Westview Press