Watershed Geomorphology, Land Use, and Water Quality Relationships in Upper Balili River Basin in Baguio City-La Trinidad, Benguet, Philippines.

Abstract

A study was conducted from June to October 2004 to assess the watershed geomorphology, land use, and water quality relationships in the Upper Balili River Basin (UBRB) in Baguio City-La Trinidad, Benguet Philippines. Data on geomorphological characteristics, soil erosion and land use, and water quality sampling stations were processed and organized in Arc View, a GIS package. Subwatersheds per steam order were identified. Data from 19 EMB-established sampling stations representing subwatersheds with measured water quality parameters (pH, turbidity, conductivity, dissolved oxygen, salinity, total suspended solid and total dissolved solids) were compared with Class “A” Freshwater Criteria on stream order basis. Results show that pH and total dissolved solids were the water quality parameters that met the Class “A” Freshwater Criteria for all sampling station orders. Two critical subwatersheds (Sto. Niño and Trancoville) were identified based on water quality standards. These subwatersheds were tested to have high values in turbidity, conductivity, salinity, total suspended solids, and total dissolved solids and have low value in dissolved oxygen because of the observed high amount of solid wastes, waste water, and floating scum with septic odor.

The UBRB geomorphology was characterized, the soil estimated, and extent of land-use assessed. The various aspects of geomorphology (shape, length of stream, drainage density, fall of stream, length of overland flow, and stream discharge), soil erosion estimate, and land-use (in percent of total subwatershed areas) of the UBRB were then correlated with water quality parameters. Geomorphological characterization show that all subwatersheds were fan-shaped; hence, peak flow and runoff were concentrated at subwatersheds' outlets at all levels of stream order; perennial stream was maintained at stream order 3 where length of stream was found highest; drainage density was greater than 1 indicative of a highly dissected watershed; slope of stream was relatively flat except the Imelda Village and Brookside sampling stations; and the longest overland flow was found in Guisad of stream order 2 while stream discharge was highest at the Balili Bridge of stream order 3.

Correlation analysis show that shape index had moderate and high degree of association only with conductivity and total dissolved solids in the third level of stream order, respectively. The length of stream had moderate degree of association only with total suspended solids in the second level of stream order and high degree of association only with total dissolved solids in the third level of stream order. The rest of the watershed geomorphological characteristics had none to low degree of association with water quality parameters. The high degree of association between shape, index and length of stream with total dissolved solids indicates that mineral contents were dissolved at the outlet of the subwatersheds and total dissolved solids were reduced as they travel along the stream.

Soil erosion had moderate degree of association only with pH but it was an invalid indication of correlation because of spurious data. The rest of the water quality parameters had varied (none-low) degree of association with soil erosion primarily because minimal amount of soil erosion (0-16 t/ha per year) was observed in the study area. Built-up/institutional area (in percent of total subwatershed areas) had moderate degree of association only with conductivity and salinity; and high degree of association with total dissolved solids. The high degree of association between built-up/institutional areas and total dissolved solids suggests strong evidence that expansion of built-up areas could significantly increase the amount of total dissolved solids, if dumping of wastes coming from residential areas was not checked.

Forest and natural areas were found to have a high degree of association with total dissolved solids; a strong evidence that expansion of forest and natural areas may significantly decrease the amount of total dissolved solids.