Ripendra Awal

Soil Water Content Sensor Response to Organic Matter Content under Laboratory Conditions

Studies show that the performance of soil water content monitoring (SWCM) sensors is affected by soil physical and chemical properties. However, the effect of organic matter on SWCM sensor responses remains less understood. Therefore, the objectives of this study are to (i) assess the effect of organic matter on the accuracy and precision of SWCM sensors using a commercially available soil water content monitoring sensor; and (ii) account for the organic matter effect on the sensor’s accuracy. Sand columns with seven rates of oven-dried sawdust (2%, 4%, 6%, 8%, 10%, 12% and 18% v/v, used as an organic matter amendment), thoroughly mixed with quartz sand, and a control without sawdust were prepared by packing quartz sand in two-liter glass containers. Sand was purposely chosen because of the absence of any organic matter or salinity, and also because sand has a relatively low cation exchange capacity that will not interfere with the treatment effect of the current work. Sensor readings (raw counts) were monitored at seven water content levels (0, 0.02, 0.04, 0.08, 0.12, 0.18, 0.24, and 0.30 cm3 cm−3) by uniformly adding the corresponding volumes of deionized water in addition to the oven-dry one. Sensor readings were significantly (p < 0.05) affected by the organic matter level and water content. Sensor readings were strongly correlated with the organic matter level (R2 = 0.92). In addition, the default calibration equation underestimated the water content readings at the lower water content range (<0.05 cm3 cm−3), while it overestimated the water content at the higher water content range (>0.05 cm3 cm−3). A new polynomial calibration equation that uses raw count and organic matter content as covariates improved the accuracy of the sensor (RMSE = 0.01 cm3 cm−3). Overall, findings of this study highlight the need to account for the effect of soil organic matter content to improve the accuracy and precision of the tested sensor under different soils and environmental conditions.

Hydraulic Fracturing and Its Potential Impact on Shallow Groundwater

Unconventional natural gas extraction from impermeable geologic formations is getting momentum in recent years due to advances in horizontal drilling and hydraulic fracturing. By 2040, shale resources are projected to account for 53 % of all natural gas production in the U.S. However, the development of unconventional oil/gas production from hydraulic fracturing has raised serious concerns about its potential impact on the quantity and quality of water resources and the environment due to the large volume of water needed and the use of toxic substances in hydraulic fracturing fluids. This paper gives an overview of the hydraulic fracturing used to extract shale gas, its potential impact on water resources, provides an overview of modeling studies and tools used to assess its potential impacts, and regulation issues related to it. The most significant risks resulting from hydraulic fracturing and shale gas development are (1) the excessive withdrawal of water, (2) gas migration and groundwater contamination due to faulty well construction, blowouts, (3) contamination by wastewater disposal, and (4) accidental leaks and spill of wastewater and chemicals used during drilling and hydraulic fracturing process.

Trends and variability of climate and river flow in context of run-of-river hydropower schemes: a case study of Sunkoshi river basin, Nepal

The increasing trend of glacier retreat and climate change/variability has direct impact on run-of-river hydropower schemes. This study analyses climate change risk in a Himalayan Sunkoshi river basin which consists of several existing/under-construction run-of-river hydropower schemes. Climate change impact has been examined by comparing observed and projected hydro-climatic trends. Projected monthly climatology (based on A1B emission scenario) of Meteorological Research Institute, Japan has been employed for the analysis. Observed annual minimum and lean season (January, February, March and April) discharges, which have larger significance for run-of-river schemes were analysed to identify any significant trend. The annual minimum and lean season monthly discharges were found with decreasing trend. Comparison of present and future precipitation pointed out that there will be 4.3% increase in monsoon (June, July, August and September) precipitation and 10.4% decrease in remaining months. Similarly, the study revealed that monthly temperature will be increased by 1.5 to 4.6°C.