Water Quality and Sediment Quality in Murum Reservoir and the Inflow and Outflow Rivers

Phang, Kong Siew (2019) Water Quality and Sediment Quality in Murum Reservoir and the Inflow and Outflow Rivers. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Water quality and sediment characteristics in a reservoir may be influenced by the inflowing water from rivers and nearby anthropogenic activities. On the other hand, water quality and sediment characteristics at downstream area may be affected by the discharge from powerhouse. There was no further literature on water and sediment quality at Murum Hydroelectric Dam after the water level reaches full supply level (FSL) of 540.0 m ASL. Thus, in this study, water and sediment were collected from 13 stations at different depth at Murum Reservoir and the downstream area. Four sampling trips were done in February, May, August and November 2017. The overall thermocline range in the reservoir was 2 – 10 m. DO at the surface water of stations in Murum Reservoir generally exceeded 5 mg/L with oxycline range in the reservoir ranging from 2 – 8 m. The thickness of Class II compliance DO at the lacustrine zone was 2 – 5 m, while 10 – 20 m for the transitional zone. TSS, BOD and COD at upstream riverine zone were significantly higher than other zones. Significantly lower TSS and turbidity at stations in lacustrine zone were caused by the stagnant state of water. Nitrogen containing nutrients present were in a descending order of OKN > TAN > nitrate > nitrite. High TP was detected at upstream riverine zone, which was found to be correlated with the high TSS measured. In water, metals detected were Zn, Al, Mn and Fe, while Cu was under the detection limit (0.005 mg/L). Discharge from the reservoir showed significantly higher concentration of CO2, TS, H2S and metals (Al, Mn and Fe) at S10 which is nearest to MPH, and it decreased as it flows 15 km downstream. Temporally, the water quality changed according to rainfall amount or the operation of the dam. Overall, in terms of WQI, the stations were in Class II (61.5 %) or III (38.5 %) according to DOE classification. Surface water of riverine zone upstream and downstream and also water at ≥ 10 m deep of riverine (downstream), transitional and lacustrine zones were all in Class III, attributed to the low DO and high TSS concentrations. Class II water was found at the surface of transitional and lacustrine zones. The dominant component in sediment collected was sand, followed by clay and the least component was silt. Organic matter was generally low (below 4 %). Other sediment characteristics are pH (4.63 – 8.32), TP (70.41 – 350.58 mg/kg) and TKN (449.71 – 1281.98 mg/kg). Metals found in sediment was in an ascending order of Cu < Zn < Mn < Fe < Al. Generally, the average metal concentration in sediment was in the lowest effect level (LEL) as recommended by the Guidelines for the Protection and Management of Aquatic Sediment Quality in Ontario. It is recommended to reduce the input of suspended solids for the benefit of sustainability of hydropower generation and the health of sensitive aquatic organism. Water quality between S8 and S9 should be maintained at Class II as it is an important stretch for the healthy growth and reproduction of sensitive aquatic organisms.

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