Environmental Assessment
Volume C-4.3
Slurry Pipeline
Fish and Aquatic Resources
Ambatovy Project
133
January 2006
4.3.5.5 Results
Riparian and Instream Disturbance
Streams and rivers along the slurry pipeline route will be directly disturbed by
riparian, bank and instream channel activities due to construction and operation
of the slurry pipeline. The extent of watercourse disturbance or loss from
riparian or instream activities cannot be accurately quantified as data is not
presently available for a majority of the potential crossings. However, an
approximate total disturbance is estimated in Table 4.3-6 based on the estimated
number of watercourse crossings, wetted widths (mean of survey data from 11
sample sites) and projected pipeline RoW graded disturbance at the crossing.
Table 4.3-6 Total Estimated Aquatic Habitat Disturbance in the Slurry Pipeline
Local Study Area
Number of Watercourses
Est. Wetted Channel
Disturbance (m)
(a)
Est. Bank RoW
Disturbance (m)
(b)
99
3,435
5,940 – 15,246
(a)
Based on average channel width (34.7 m) from 11 measured sites.
(b)
Based on cleared / graded width of 30 to 77 m x two banks.
Analysis of fish species composition at the sample sites correlated the presence
of predominately indigenous (endemic and native) fish species to the presence of
largely natural or slightly modified forest stream habitat (40% of sample sites).
Habitat loss and alterations could interfere with these populations. Assuming
open cut installation of the water pipeline, effects will be primarily a short-term
disturbance of riparian and instream habitat and limited to the construction
period, with low impact. Through sedimentation and erosion control design
measures, the overall impact is predicted to be negligible. However, long-term
high impacts could occur at watercourses because of the extent of soil grading
and cuts necessary to achieve the maximum grade of 15% for the pipeline, and
the local combined effects of “road” use.
In addition to the slurry pipeline RoW, access roads will be required for people
and equipment. Substantial upgrading and rebuilding will be required for most
of these roads. The access roads will be routed along streams and stream valleys
in some cases, and some new bridges will be required at river crossings, in
addition to an undetermined number of culvert or ford crossings of smaller
watercourses. As many of these watercourses are located in disturbed habitats,
impacts may be low, based on reduced sensitivity of biota to disturbance. The
effects of any road construction will be generally short-term and low impact;
however, long-term, permanent disturbance could occur depending on the type of
