Comparative Study Between South-Jema and Kesum Catchment
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Date
2020-06-06
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Addis Ababa University
Abstract
The study comprises of South-Jema and Kesum catchment, is located in the central highland. It is geographically confined within 38°50´00´´E to 39°00´00´´ E longitude and 8°45´00´´N to 10°00´00´´N latitude covering a total area of 5,683 km2. The study has been conducted with objective to make a comparative analysis of recharge and hydrochemistry.
From the hydro chemical data analysis, concentrations of Na and Ca were found to be higher and being the dominant species in both catchment whereby concentration of Na shows an increment towards the downstream part of both catchments whereas concentration of calcium doesn’t shows any decrement towards the downstream part of south-Jema catchment but a decrement in concentration of Ca has been observed in the downstream part of Kesum catchment with rise in TDS. The anion species are dominated by bicarbonates, showing an increment towards the downstream part of both catchments.
As evidenced from hydro-chemical Data, there exists a clear evolutionary trend in increment of TDS towards the downstream part of both catchments.
Four types of groundwater facies exist in the region ranging from Ca-HCO3 water types mainly concentrated in representing shallow groundwater circulation with relatively short sub-surface residence time to a Ca-NaHCO3/Na-Ca-HCO3 water type representing evolutionary tend of groundwater along its flow path towards the downstream of Kesum catchment.
The spatially distributed groundwater balance model, Wetspass has been used in seasonal and annual estimation of groundwater resources, actual evapotranspiration and surface runoff of both catchments. By coupling of physical and hydro-metrological characteristics of the watershed, the wetspass have simulated the average annual long-term groundwater recharge, actual evapotranspiration and surface runoff in South-Jema catchment is found to be 122.02 mm/ year, 380.64mm/ year and 534 mm/year respectively. In the case of kesum catchment, the average long-term groundwater recharge, evapotranspiration and surface runoff is found to be 114.91 mm/year, 455.61mm/year and 410.08 mm /year.
The long-term annual precipitation in South-Jema catchment (1023 mm) is distributed as 11.92% recharge, 37.14% evapotranspiration and 52.19% runoff, indicating almost half of the precipitation feeding the watershed is lost due to surface runoff. In the case of Kesum catchment the long-term annual precipitation (973.81 mm) is distributed as 11.8% recharge, 46.7 % evapotranspiration and 42. 11% surface runoff.
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Keywords
Sodium, Calcium, Bicarbonate, Water Types, Ground Water, Recharge, Actual Evapotranspiration, Surface Runoff, Wetspass