Toward Understanding the Cumulative Impacts of Roads in Upland Agricultural Watersheds of Northern Thailand.

TitleToward Understanding the Cumulative Impacts of Roads in Upland Agricultural Watersheds of Northern Thailand.
Publication TypeJournal Article
Year of Publication2004
AuthorsZiegler A, Giambelluca T, Sutherland R, Nullet M, Yarnasarn S, Pinthong J, Preechapanya P, Jaiaree S
ContactAuthorasb@cgiar.org, adz@hawaii.edu
JournalAgriculture, Ecosystems & Environment
Volume104
Start Page145
Pagination14
KeywordsASB, erosion, land degradation, southeast asia, tropical hydrology/geomorphology, Unpaved roads
AbstractThis paper describes the interactions of various physical processes that allowunpaved roads to contribute disproportionately to basin-wide runoff and stream sediment in the 93.7 ha Pang Khum Experimental Watershed (PKEW) in northern Thailand. Many road sections in PKEW are constant sources of sediment entering the stream during most rain events because: (1) Horton overland flow is generated on the compacted surfaces after small depths of rainfall; (2) surface preparation processes, including vehicle detachment and maintenance activities, renew the supply of easily transportable surface sediment on inter- and intra-storm time scales; (3) erosion of the road surface is accelerated in locations where slopes are steep, overland flow distances are long, and/or vehicle usage is high; (4) surface runoff typically exits from the road directly into the stream.Owing to these collective processes, sediment delivery rate on PKEW roads is more than an order of magnitude higher than that on adjacent fields (≈120Mgha−1 per year versus 9Mg ha−1 per year). Thus, unpaved roads appear to be on the same order of importance as agricultural lands in contributing sediment to the stream network, despite occupying a fraction of the total surface area in the basin (≈0.5% versus 12%). A more thorough assessment of linkages between all hill slope runoff/sediment sources and the stream network, however, is still needed to fully evaluate the relative impacts of roads versus those of agriculture practices in PKEW.
URLhttp://www.asb.cgiar.org/pdfwebdocs/AGEE_special_Ziegler_Towards_understanding.pdf