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Characterization of Groundwater Discharge to Rivers in the Shire River Basin, Malawi
Laura Kelly,
Douglas Bertram,
Robert Kalin,
Cosmo Ngongondo
Issue:
Volume 5, Issue 4, December 2019
Pages:
127-137
Received:
10 October 2019
Accepted:
4 November 2019
Published:
8 November 2019
Abstract: This study investigates groundwater discharge to rivers in the Shire River Basin, Malawi, using the base flow index (BFI) approach. The BFI represents the baseflow component of a river and is often used as a proxy indicator of groundwater discharge to a river. The smoothed minima method was applied to river flow data from 15 gauges in the Basin (ranging from 1948 to 2012) and the Mann-Kendall (MK) statistical test was used to identify trends in the BFI. The BFI results indicate that groundwater plays an important role in contributing to river flows in the SRB, especially in the dry season. Expressing the BFI as a percentage, these values indicate that annual groundwater discharge to the river’s ranges from 19% in the Rivirivi River to 97% in the Shire River. Seasonally, minimal difference was found between the annual and the wet season BFI. Generally, the dry season BFI was higher than those of the wet season with most rivers increasing to >75%. Groundwater data supported the seasonal fluctuations identified in the BFI data, however, there were no groundwater monitoring boreholes in close proximity to any of the river gauges for in-depth analysis. The results also showed long term trends in the BFI data indicating behavioural changes in the river baseflow and groundwater discharge. In some areas, the declines in BFI indicate that groundwater discharge has been reducing over time due to declines in groundwater levels. This is a concern for the sustainable management of water resources in the Basin. The findings of this study provide important new knowledge on the seasonal and long-term behaviour of groundwater discharge to rivers in the Basin which will be crucial for supporting sustainable water resources management practices. The results will be particularly useful to the new National Water Resources Authority within the Malawian Government, who will oversee catchment management plans.
Abstract: This study investigates groundwater discharge to rivers in the Shire River Basin, Malawi, using the base flow index (BFI) approach. The BFI represents the baseflow component of a river and is often used as a proxy indicator of groundwater discharge to a river. The smoothed minima method was applied to river flow data from 15 gauges in the Basin (ra...
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Hydrologic and Structural Safety Evaluation of Aged Concrete Gravity Dam Using Finite Element Method
Tafesse Fitensa,
Medhanye Biedebrhan,
Sisay Simachew
Issue:
Volume 5, Issue 4, December 2019
Pages:
138-154
Received:
9 August 2019
Accepted:
6 November 2019
Published:
17 November 2019
Abstract: History shows that several dams were failed and discharged the stored water which causes incalculable damage on life and property. Several researches disclosed that the methods used to design and re-evaluate concrete gravity dams after the 1970s have shown significant advancement. This starts when contemporary structural analysis methods such as a finite element method were incorporated into computer programs. Structural safety evaluation criterion, design standards and guidelines were also updated. Hence, periodical structural safety evaluation of older dams using state of art techniques is an important activity of the dam experts to ensure a safe operation of dams. This study was focused on hydrological and structural safety evaluation of Koka dam by using HEC-HMS and Abaqus models, based on USACE load combination. The Hydrologic Modeling System, HEC-HMS model was calibrated and used to determine the reservoir elevation reached when the peak outflow resulted from the Probable Maximum Flood (PMF) passes over the spillway. Result of the HEC-HMS model shows that the elevation reached by peak outflow was 1.4m lower than the dam crest which indicates no overtopping of the dam due to PMF. The peak reservoir elevation reached when the peak outflow from PMF passes over spillway was used to apply hydrostatic load on the dam. The dam was analyzed by static general method in Abaqus model. The results of Abaqus model indicate that the maximum principal stress in the dam body was under tensile sense near the heel during PMF with the peak magnitude of 0.602MPa. The corresponding minimum principal stress was under compressive sense throughout the base with the peak magnitude of -0.431MPa. All the results were below the compressive and tensile strength, hence, the dam concrete does not fail under PMF due to material overstressing. The aging of concrete, do not change the stress, but displacement. The results of displacement clearly show a significant increment. This result tells that the aging of concrete reduces the stiffness of the dam and increases its flexibility.
Abstract: History shows that several dams were failed and discharged the stored water which causes incalculable damage on life and property. Several researches disclosed that the methods used to design and re-evaluate concrete gravity dams after the 1970s have shown significant advancement. This starts when contemporary structural analysis methods such as a ...
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Responses of Soybean (Glycine max L.) Varieties to NPS Fertilizer Rates at Bako, Western Ethiopia
Dame Oljirra,
Tasisa Temesgen
Issue:
Volume 5, Issue 4, December 2019
Pages:
155-161
Received:
27 September 2019
Accepted:
6 November 2019
Published:
27 November 2019
Abstract: Soybean (Glycine max. L) is among the most important legume crops produced in western Ethiopia. However, declining soil fertility and poor soil fertility management practices decrease yields. A field experiment was conducted in Bako Agricultural Research center during 2018 main cropping season to investigate the effect of NPS rates on yield and yield components of soybean varieties and to identify economically feasible rates of blended NPS rate that increase the productivity. Dhidhessa, Ethio-yugoslavia and Wello of soybean varieties and five rates of NPS (0, 50,100,150 and 200 kg ha-1). The experiment was laid out in arrangement in RCBD with three replications. The highest hundred seed weight (16.9g) was recorded from Ethio-yugoslavia and the lowest (15g) from Wello. Significant effect was exhibited on days to 50% flower, above ground biomass yield and seed yield due to main effects of NPS rate. The highest (55.78) and the lowest (53.78) numbers of days to flowering were recorded due to application of 200 kg NPS ha-1 and 0 kg NPS ha-1, respectively. The tallest (81.63cm) and the shortest (65.60 cm) plants were recorded under 200 kg NPS ha-1 and 0 kg NPS ha-1, respectively. The highest (8718 kg ha-1) above ground dry mass was obtained at the highest rate of 200 kg NPS ha-1 and the lowest (6910 kg ha-1) was due to 0 kg NPS ha-1. The highest (2763 kgha-1) seed yield was recorded from the application of 100 kgha-1 NPS rate and the lowest (1935kgha-1) seed yield was recorded from nil application of NPS fertilizer rate. The best combination with high grain yield and economic benefit is 100kgha-1 NPS fertilizer rate with Didhessa Variety. The major measured parameters contributing for grain yield were above ground biomass, number of pod per plant and no of primary branch per plant. This experiment generally confirmed as 100kgha-1 NPS for soybean was appropriate. This trial was conducted at strong acid soil, these it is expected as the plants might not have access to use the applied fertilizer and if it was conducted with lime application the responses might be changed. Thus, it can be concluded that combined application of 100 kg ha-1 of blended NPS with Dhidhessa variety could be used at similar agro ecology. However, since the study was conducted for one season at one location, it has to be repeated over seasons and locations to make a conclusive recommendation.
Abstract: Soybean (Glycine max. L) is among the most important legume crops produced in western Ethiopia. However, declining soil fertility and poor soil fertility management practices decrease yields. A field experiment was conducted in Bako Agricultural Research center during 2018 main cropping season to investigate the effect of NPS rates on yield and yie...
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Modelling Hydrological Processes on Agricultural Used Land for Optimisation of Small Hydropower Cascade in the (Upper) Wuyang River Basin of Southwest China
Mariusz Merta,
Harald Sommer,
Zhengyue Jin
Issue:
Volume 5, Issue 4, December 2019
Pages:
162-173
Received:
4 November 2019
Accepted:
11 December 2019
Published:
23 December 2019
Abstract: Reliable estimations of stream flow generated from catchments are required as part of the information sets that help policy makers making reasonable decisions on water planning and management. The characteristics of the streamflow time series that influence water resources system modelling and planning can include the sequencing of flows on daily or longer time steps, spatial or temporal variability of flow, seasonal distribution and characteristics of high and low flow. This is mainly based on agricultural and natural land use. Hydrological modelling of the water supply in the river basin is of great importance in planning and optimization of hydropower plants. Those single plants are often integrated into complex cascades and are a significant part of electrical production depending on the natural inflow. However, in many parts of the world the necessary data are missing. The central question of this study was if is it possible to model the water and discharge regime of a catchment area on the basis of available public data, esp. land use, sources in order to ensure single site evaluation and optimize energy production of hydropower plants.
Abstract: Reliable estimations of stream flow generated from catchments are required as part of the information sets that help policy makers making reasonable decisions on water planning and management. The characteristics of the streamflow time series that influence water resources system modelling and planning can include the sequencing of flows on daily o...
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Predicting Aquifer Storage Properties Integrating Geoeletric Methods with Dynamically Derived Geomechanical Parameters in Parts of Cross River State, Nigeria
Issue:
Volume 5, Issue 4, December 2019
Pages:
174-183
Received:
9 December 2019
Accepted:
8 January 2020
Published:
11 February 2020
Abstract: Predicting subsurface rocks’ storage properties is a fundamental problem of groundwater prospecting and potential evaluation for planning of long term abstraction wells. Water in aquifers is stored and or released from elastic storage and gravity drainage. Aquifer storage parameters are traditionally determined from pumping tests data which are seldom available until wells have been drilled. Confined aquifer storativity (S) is estimated as a function of rock lithology and thickness of the aquifer using the rule of thumb equation S = 3.0 × 10-6b, but S = Ssb neglecting the effect of porosity and compressibility. The storativity equation assumes that all aquiferous rocks have a constant specific storage even though specific storage is directly dependent on rock porosity and most importantly rock grain compressibility which differs with lithology. In this study, apparent resistivity data derived from field resistance measurements in 31 locations were interpreted to infer geolectric layers lithologies and thicknesses. To determine the rock grain compressibility for computation of the specific storage, vertical stress at the aquifer depth was estimated using average densities of the interpreted subcrustal rocks. Results show that rock mineral grain compressibility varies from 7.915 × 10-7 to 9.235 × 10-5/Pa, porosity from 0.08 to 1.64 with the weathered overburden and sandstones having the higher porosities; specific storage vary from 8.32 × 10-6 to 1.80 × 10-3 and storativity ranges from 3.161 × 10-6 to 1.96 × 10-3. Clearly, results indicates that the specific storage differ predictably with rock type and consequently the storativity of the different aquifers.
Abstract: Predicting subsurface rocks’ storage properties is a fundamental problem of groundwater prospecting and potential evaluation for planning of long term abstraction wells. Water in aquifers is stored and or released from elastic storage and gravity drainage. Aquifer storage parameters are traditionally determined from pumping tests data which are sel...
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