Ecoregional Assessment of Biological Diversity in East Kalimantan

East Kalimantan Ecoregional Assessment: Chapter 1 – Background & Analysis Process
Major Rivers and Lakes Target Ecological Systems
No standard, direct measure of the hydrologic condition of the Major Rivers themselves was
available for this effort - at least not one that would enable a relatively objective comparison
between any two rivers in the planning unit. Therefore, we developed a somewhat indirect
assessment of functionality and condition of the rivers by ranking the condition of their
surrounding vegetation coupled with flow contribution of their upper watersheds.
In accordance with the zone recommended by the Indonesian Forests Department for large
rivers (U.U. No. 41:1995), and by local experts on river sedimentation factors, the presence
of healthy forests or other natural vegetation bordering rivers on both sides to a width of at
least 500 meters is considered essential to the viability of rivers. Such a vegetation buffer
reduces sedimentation and pollution loads into the river, shades and reduces water
temperatures, protects its banks and physical environments for fish and other fauna, and
supplements through litter-fall the nutrients in the river along various stages of its course.
Therefore, viability for the major rivers was calculated on the basis of the condition of the
forests that border three segments of a river, namely, 1) the Upper Catchment Area, 2) the
Mid-stream Buffer Zone and 3) the terminal Delta area. Viability assessments for these three
segments are described as follows:
a. Upper Catchment Area
Identified by aggregates of the sub-catchments that define the smallest upper catchment
polygon that can be generated using ESRI Hydrological Modeling (Version 1), using 250
cells as a minimum input. Only catchment areas for the first order rivers that have a
maximum flow accumulation value in the 1 st -2 nd standard deviation grouping as generated by
ESRI were considered (Appendix III.A for an example).
b. Midstream Buffer Zone
Defined by a width of 500 meters on both sides of the stream. The values for mid-stream
buffer zones were calculated by assessing the combined areas of the mid-stream buffer zones
of the river branches that are fed by the upper catchments. Condition of these combined areas
was calculated using the same approach as to estimate condition of vegetation inside an
element occurrence (see terrestrial section above).
c. Delta Areas
The condition of the terrestrial target ecological systems of Mangrove Forest, Freshwater
Swamp Forest and Peat Forest occurrences that are in contact with the Rivers at or near their
terminal deltas (See Fig.2.C.1). These ecological systems have already been ranked prior to
their selection and these same values are included in the overall rank for this section of the
Major River target occurrence.
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