Dar zarrouk parameters, Slides of Advanced Physics

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 - Ahmed Sami 

• Ahmed Al Sayed
• Abdelftah Mohamed - Mostafa Yassen

Using geoelectric soundings

for estimation of hydraulic

characteristics of aquifers in

the coastal area of Lagos,

southwestern Nigeria

Twenty-one VES were conducted using.

Shlumberger array with a maximum half current

electrode (AB/2) of 100 m giving total spread of

200 m

Data were interpreted using partial curve matching technique and assisted 1-D Forward modeling with WINRESIST software. The qualitative interpretation revealed KQ curves (ρ1 < ρ2 > ρ3 >

. ρ4) and KH curve (ρ1 < ρ2 > ρ3 < ρ4)

The geoelectric section generated from the results of the VES revealed a four geo-electric layers; these include topsoil with resistivity ranging from 213-5404 Ωm, dry sand with resistivity values vary from 301to 17178 Ωm, saturated sand with resistivity varying from 110 to1724 Ωm and sand (saline water content) with resistivity values of between 8 and 97 Ωm. The major aquifer in the area occurs at the third geoelectric layer The depth to this aquifer is of between 0.7m and 6.0m and the layer thickness is between 0.2 m and 19.9 m

It has high transverse resistance, high transmissivity, and high hydraulic conductivity indicating that the aquifer can transmit water at higher rate and sustain the need of the community

INTRODUCTION. 1 Groundwater as one of the main sources of potable water supply for domestic, industrial and agricultural uses has been under intense pressure of degradation an contamination due to urbanization, Industrial, agricultural

. related activities and saline water intrusion from the ocean The impact of these contaminations on soil and groundwater is alarming with years of devastating effects on humans and the ecosystem

Despite the fact that Lagos coastal environment is surrounded by water, access to potable water has always being their major problem due to saline water intrusion into their fresh water aquifer, which is very common in areas that have hydraulic continuity with the ocean. Due to this problem, the Lagos coastal people depend mainly

. on surface aquifer to meet their water demand Therefore, understanding of saline water intrusion is essential for the management of coastal water resources. The knowledge of the hydraulic characteristics of an aquifer is very important in the determination of its potential as potable water aquifer

LOCATION OF THE STUDY AREA The study area (Lekki free zone) is located between Latitude 6°25’ and 6°27’ north of the equator and Longitude 3°57’ and 4°03’ (Fig. 1). It is found within the sedimentary basin (Dahomey basin) of southern The landmass of the study area consists of islands, coastal sand banks, high forest (i.e mangrove or swamp and rain forest). western Nigeria.

The greater part of the rain forest is

interspersed with farms and villages.

The exception so far is the swamp forest

in which conditions are too harsh for

farming (Agabiet et. al; 1994) but which

are now being exploited for farming and

fishing. The area is accessible through

the major road that cut across Lekki-

Free zone, Mobido and Idaso.

GEOLOGY OF THE AREA

Lagos which falls within Dahomey basin

and lies on the stratified series of

sedimentary rocks made up of silt, clay

and sand of various sizes and

composition basins (Whiteman, 1982).

The studied area (Lekki free zone) is

made up of Benin formation (Miocene to

Recent), Recent littoral alluvial, lagoon

and Coastal Plain Sands deposits. The

fluctuation of the sea level during the

Quaternary times affected the formation

. A common feature of the alluvium

sediments found in the area is that they

consist of mainly sands, littoral and

lagoon sediments formed between an

old barrier beach and a relatively

younger barrier beach as well as

Coastal Plain Sands. The sediments

range in size from coarse to medium

grained, clean white loose sandy- soil

that graded into one another towards

the lagoon and near the mouth of the

larger rivers.

Agenda Dar-Zarrouk Parameters The story of this presentation SLIDE 19 Let it begin! Used Array Used Array Dar-Zarrouk Parameters Dar-Zarrouk Parameters END END Transverse Resistance Transverse Resistance Protective Capacity Protective Capacity Longitudinal Conductance Longitudinal Conductance HYDRAULIC CONDUCTIVITY HYDRAULIC CONDUCTIVITY Transmissivity of the Aquifer Transmissivity of the Aquifer Porosity and Formation factor Porosity and Formation factor Relation Relation

Using the Schlumberger electrode array Used Array We are very glad to meet you. SLIDE 20 What we are talking about today.  (^) Twenty-one VES points were occupied by the side of the major road that runs through the study area  (^) The investigation was carried out with the aid of Pasi Digital Earth Resistivity Meter.  (^) The current electrode is symmetrically increased  (^) potential electrode is fixed at its initial distance  (^) AB/2 ≥ 5(MN/2) was satisfied.  (^) AB/2 was increased to a maximum spread of 100 m  (^) MN/2 to a maximum of 5m  (^) The apparent resistivity (Pa) is plotted against the corresponding half electrode spacing(AB/2) on a bi-logarithm graph to generate the sounding curves. Pasi Digital Earth Resistivity meter