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Application of MIKE SHE software for estimation of groundwater recharge in Ogun and Oshun basins, southwestern Nigeria

Oke Muritala O.

Journal of Water and Land Development

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2020

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no. 45

86--93

EN

MIKE SHE software was used to estimate recharge into the aquifers of Ogun and Oshun Basins. Abeokuta within the Ogun Basin and Oshogbo in the Oshun Basin are sub-divided vertically into two components: atmosphere, and unsaturated zone. The atmosphere zone comprises of rainfall and potential evapotranspiration, while the unsaturated zones, comprises of the Basement Complex and Sedimentary rock. Daily records from two rainfall stations, Oshogbo station (2008–2011) and Abeokuta station (2010–2014) water years were obtained for simulation of groundwater recharge processes using MIKE SHE model. The simulation results showed that daily groundwater recharge is influenced by rainfall and ranges from 0 mm∙day–1 in January when there was an insufficient rainfall in the two stations to 10.89 mm∙day–1 in Abeokuta and 29.85 mm∙day–1 in Oshogbo in the month of August when the soils had attained field capacity. The study found out that there are more daily groundwater recharge in Oshun basin compared to that of Ogun basin. This was alluded to more rain-fall and less evapotranspiration recorded at Oshun basin as compared to Ogun basin coupled with the sedimentary soil which allows more movement of water into the aquifer of the basin. It is recommended MIKE SHE model should be used to estimate recharge in other basins in Nigeria and Africa for quick and effective daily recharge calculations to permit better and scientific decision making in these areas.

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Assimilation experiments in the Gdansk Basin (the south-eastern Baltic): How useful are the sea level data from coastal tide gauges for modelling of hydrophysical fields?

Jankowski A., Jędrasik J.

Oceanological and Hydrobiological Studies

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2007

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Vol. 36, No.4

105-128

EN

In the Baltic modelling research, assin.ilation techniques were developed with advance. They were-concerned to model assimilated basic parameters and observed them directly. In present paper, the most important was the assimilation of surface information and its projection deep into temperature and salinity fields. In oceanic investigations altimetry viewed from satellite was the sea level changes projected far inside and predetermined surface-to-subsurface correlations. To obtain improved modelled hydrophysical fields, sea level variations measured at coastal gauges and efficient data assimilation were taken into account. A data assimilation algorithm has been developed and used in conjunction with a three-dimensional baroilinic model of the Baltic Sea. It was based on a time and space weighted nudging technique. The sea level data were inserted continuously by updating the model solution every time step. Several sensitivity experiments with different values of time and spatial weighting scales were performed. In first series of experiments, only sea level data (SL) were assimilated. In the next simulations, seawater temperature (SWT) and seawater salinity (SWS) related directly to SL were assimilated. To evaluate the effectiveness of the assimilation scheme, modelled sea level series and vertical profiles of seawater temperature and salinity in selected coastal gauges in the Gdansk Basin were examined. Evidently low but statistically essential correlation coefficients indicated nonlinear character of vertical mixing and transfer processes. Decreasing errors obtained while comparing the model results to a control case without assimilation confirmed a real transfer of surface information deep and usefulness of such approach in modelling.

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Application of a σ-coordinate baroclinic model to the Baltic Sea

Jankowski A.

Oceanologia

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2002

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No. 44 (1)

59-80

EN

A three-dimensional (3-D) sigma-coordinate baroclinic model is used to investigate water circulation and thermohaline variability in the Baltic Sea. Two versions of the horizontal resolution of ~ 10 km and ~ 5 km with 24 sigma-levels in the vertical are considered. The model is based on the Princeton Ocean Model code of Blumberg & Mellor (1987) and Mellor (1993), known as POM. This paper presents details of simulation strategies and briefly discusses the 'reality' of the results of modelling. The model's capabilities of simulating the characteristic hydrographic features of the Baltic Sea were tested for 3 months (August-October 1995), a simulation related to the period of the PIDCAP'95 experiment (Pilot Study for Intensive Data Collection and Analysis and Precipitation) (Isemer 1996). The model results are compared with the in situ measurements of temperature and salinity at selected hydrographic stations, collected during cruises of r/v 'Oceania' in September and October 1995. Comparison of computed and measured temperature and salinity shows that the model reproduces the vertical structure of seawater temperature and salinity in relatively good accordance with the in situ observations. The differences between the calculated and observed values of temperature and salinity are c. 1-2oC and c. 1-2 PSU, depending on the location of the hydrographic station.

4

Wind-induced variability of hydrological parameters in the coastal zone of the southern Baltic Sea - a numerical study

Jankowski A.

Oceanological Studies

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2000

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Vol. 29, No. 3

5-34

EN

Abstract The wind-produced variability of temperature, salinity and velocity in the coastal zone of the southern Baltic Sea have been investigated with the help of a three-dimensional F-coordinate baroclinic model. The model was based on the Princeton Ocean Model code of Mellor (1993), known as POM. The main intention of this study was to reproduce the variability of the hydrological conditions as the response of stratified seawaters to the model atmospheric forcing of three successive storms. Winds of constant speed from eight directions over the Baltic during each storm were considered. The presentation of results is limited to the area along the Polish coasts of the Baltic Sea, where the complicated bottom topography exerts a crucial influence on water movements. The numerical model runs show that winds can play an important role in the water exchange between the coastal region and the open sea, generating intense fluctuations of hydrological parameters. When winds are from the SE, E and NE, coastal upwelling is frequent along the Polish Baltic coast (Bychkova and Victorov 1987, Bychkova et al. 1988, Urbanski 1993). The results calculated with the use of the POM code are in agreement with the results obtained using the z-level model (Krauss and Brügge 1991) and from studies in the Great Lakes and in other upwelling areas (Bennet 1974, Krauss 1979, Fennel 1986).