Abstract:
Our study focused on quantifying the alterations of streamfow at a weir site due to the construction
of a mini-hydropower plant in the Gurugoda Oya (Sri Lanka), and evaluating the spatial responses
of benthic macroinvertebrates to altered fow regime. The HEC–HMS 3.5 model was applied to
the Gurugoda Oya sub-catchment to generate streamfows for the time period 1991–2013. Pre weir fows were compared to post-weir fows with 32 Indicators of Hydrologic Alteration using
the range of variability approach (RVA). Concurrently, six study sites were established upstream
and downstream of the weir, and benthic macroinvertebrates were sampled monthly from May
to November 2013 (during the wet season). The key water physico-chemical parameters were also
determined. RVA analysis showed that environmental fow was not maintained below the weir. The
mean rate of non-attainment was ~ 45% suggesting a moderate level of hydrologic alteration. Benthic
macroinvertebrate communities signifcantly difered between the study sites located above and
below the weir, with a richness reduction due to water diversion. The spatial distribution of zoobenthic
fauna was governed by water depth, dissolved oxygen content and volume fow rate. Our work
provides frst evidence on the efects of small hydropower on river ecosystem in a largely understudied
region. Studies like this are important to setting-up adequate e-fows.
