Faculty of Engineering

Permanent URI for this communityhttps://rda.sliit.lk/handle/123456789/4203

Browse

Filters

2015 - 20172

Advanced Search

Filter by

Settings

Author: search.filters.author.Gomes, P. I. ASubject: search.filters.subject.ephemeral streams

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    PublicationEmbargo
    Eco‐hydraulic evaluation of herbaceous ecosystems below headwater dams without a base flow: Observing below dam reaches as new stream sources
    (Wiley Online Library, 2017-01) Gomes, P. I. A; Wai, O. W. H; Yan, X. F
    The roles of headwater streams are usually underestimated and inadequately managed compared with the larger downstream river systems. This two and half-year study covering several wet and dry seasons evaluated the impacts of small headwater dams without a base flow on downstream herbaceous dynamics. Results showed herb aerial cover and diversity below dams (new stream sources) are unique and different to original stream sources as well as to a comparable unregulated reach. The geomorphological habitats formed subsequent to damming did not show major influence on aerial cover of herbs; nevertheless, diversity showed a clear dependence. Downstream of dams were dominated by Acorus gramineus, which had >40% aerial cover, and this figure increased up to 60% within 2 years (in between a major flood event). Simultaneously, downstream herb diversity decreased by 33%. However, diversity and aerial cover of the unregulated reach and original sources remained more or less the same. Herb pulling tests (simulating an uprooting mechanism during a flood) showed A. gramineus can withstand an eightfold higher force than the other herbs, especially in concrete surfaces and rock/sand pools. The estimated shear force on bed during the major flood was several folds less than the observed. This suggests downstream of dams behave opposite to the conventional understanding that large floods are considered as an agent of restoration.
  • Thumbnail Image
    PublicationEmbargo
    In‐stream physical heterogeneity, rainfall aided flushing, and discharge on stream water quality
    (Water Environment Federation, 2015-08) Gomes, P. I. A; Wai, O. W. H
    Implications of instream physical heterogeneity, rainfall-aided flushing, and stream discharge on water quality control have been investigated in a headwater stream of a climatic region that has contrasting dry and wet seasons. Dry (low flow) season's physical heterogeneity showed a positive correlation with good water quality. However, in the wet season, physical heterogeneity showed minor or no significance on water quality variations. Furthermore, physical heterogeneity appeared to be more complementary with good water quality subsequent to rainfall events. In many cases stream discharge was a reason for poor water quality. For the dry season, graywater inputs to the stream could be held responsible. In the wet season, it was probably the result of catchment level disturbances (e.g., regulation of ephemeral freshwater paths). Overall, this study revealed the importance of catchment-based approaches on water quality improvement in tandem with in-stream approaches framed on a temporal scale.