Groundwater level trend analysis using the statistical auto-regressive HARTT method
January 22nd, 2020
Guesh Zeru, Tena Alamirew, Haile A. Shishaye, Megersa Olmana, Nata Tadesse, Michael J. Reading
Received 2019/07/12, Accepted 2019/10/04, Published 2020/01/22
Guesh Zeru1), Tena Alamirew2), Haile A. Shishaye3), Megersa Olmana4), Nata Tadesse5), Michael J. Reading5)
1) School of Water Resource and Environmental Engineering, Haramaya University, Ethiopia
2) Water and Land Resource Center, Addis Ababa University, Addis Ababa, Ethiopia
3) Southern Cross Geoscience, Southern Cross University, Lismore, New South Wales, Australia
4) Tshwane University of Johannesburg, South Africa
5) Mekelle University, Mekelle, Ethiopia
In this study, the Hydrograph Analysis: Rainfall and Time-Trends (HARTT) model was used to determine the contribution of climatic and non-climatic stresses on groundwater levels in the Lake Haramaya well-field, Ethiopia. Monthly precipitation and monitored water-level data were used as explanatory variables of the method. Variability in rainfall explained 81.3% of groundwater levels using 2-month average time-delay. The coefficient of the impact of rainfall on groundwater level (K1) was found to be 0.00562 ± 0.0007 mm. This K1 value indicates that a 1 mm increase in rainfall from the annual average rainfall raises the groundwater-level by 0.00562 ± 0.0007 mm, while 1 mm decrease in rainfall causes a 0.00562 ± 0.0007 mm drop in groundwater-level in the area. However, the average falling trend of the groundwater level (K2) was 1.51 ± 0.133 m/year, even with rainfall causing water-levels to rise between 1.01 to 3.29 m/year. With decreased rainfall, rainfall accounted for about 19.5% of the total-drawdown, while 80.5% was due to cumulative effects of non-climatic variables. This shows that rainfall inputs are negated by cumulative non-climatic stresses leading to the long-term net decline in groundwater level. Projected water-level results show that groundwater levels will be below pumping positions in <24 years which may have dire consequences for local landowners.
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