WFD – Identification of Groundwater Bodies

The Water Policy Framework Regulations, 2004 consider a groundwater body as a coherent sub-unit in the Water Catchment District to which the Environmental Objectives should be applied.  Hence the main purpose of identifying these bodies is to enable their quantitative and qualitative status to be accurately described and compared to the Environmental Objectives.

The term ‘body of groundwater’ should therefore be understood in the context of the hierarchy of relevant definitions provided under Regulation 2:

Body of Groundwater, under Regulation 2

Regulation 2.2

‘Groundwater’ means all water, which is below the surface of the ground in the saturated zone and in direct contact with the ground or sub-soil.

Regulation 2.11

‘Aquifer’ means a subsurface layer or layers of rock or other geological strata of sufficient porosity and permeability to allow either a significant flow of groundwater or the abstraction of significant quantities of groundwater.

Regulation 2.12

‘Body of groundwater’ means a distinct volume of groundwater within an aquifer or aquifers.

The Maltese Islands are mainly composed of two porous and fissured limestones:

  • the Upper Coralline Limestone, and
  • the Globigerina-Lower Coralline Limestone formations.

These are  separated by a relatively thin layer of clayey and marly material, the Blue Clay formation, which is sometimes overlain by the Greensand formation. 

The Upper and Lower Coralline Limestones are considered to function as aquifer rocks; with the Globigerina Limestone functioning only locally as an aquifer where highly fractured.

The subsequent delineation of ‘bodies of groundwater’ must therefore enable an appropriate description of the quantitative and qualitative status of groundwater such that the relevant objectives of the Regulations can be achieved.  The initial delineation of ‘bodies of groundwater’ in the Maltese Water Catchment District has been strictly based on geological boundaries and has resulted in the identification of sixteen groundwater bodies as described below.

A map of the Groundwater Bodies may be downloaded from here.

From a structural point of view, the island of Malta can be divided into two parts: the northern and the central/southern regions; the limit being marked by the sealing Pwales fault.  In the major part of the island, south of the Pwales fault, the Upper Coralline Limestone and the Lower/Globigerina Limestone aquifers are stacked vertically.  The Lower Coralline Limestone aquifer is in direct contact with sea-water and due to the density contrast of fresh-water and salt-water a ‘Ghyben-Herzberg’ system is developed: – a freshwater lens floating on saltwater with a thickness approximately 36 times below sea level than the height of the freshwater surface above sea-level.  The Upper Coralline Limestone aquifer in these regions is perched above the Blue Clay aquiclude formation and is divided into two hydrologically separate blocks due to faulting; namely the Rabat-Dingli and the Mgarr-Wardija Plateaux.

The northern part of the island is divided by a NE-SW fault system into a succession of horst and graben-like structures; the graben being occupied by rather flat valleys separated by ridges.  This structure with parallel compartments separated by faults leads to the point that the resulting aquifer blocks are considered as independent  from one another from a hydrogeological point of view.  Distinct ‘bodies of groundwater’  are thus developed in the hydrologically separate aquifer blocks at Pwales Valley, Mizieb, Mellieha Ridge, Mellieha Bay and Marfa Ridge regions.

The island of Comino supports a distinct ‘Ghyben-Herzberg’ groundwater body within the Upper Coralline Limestone.

In the island of Gozo, the Lower Coralline Limestone aquifer sustains another ‘Ghyben-Herzberg’ system displaced over the whole island except for a small region around the harbour of Mgarr in the south-eastern part of the island, where the Blue Clay formation occurs at sea-level due to faulting.  The Upper Coralline Limestone outcrops in geographically separate areas, namely at Ghajnsielem, Nadur, Xaghra, Zebbug and Victoria/Kercem giving rise to separate aquifer blocks sustaining distinct bodies of groundwater.

The ‘bodies of groundwater’ thus identified are as follows:

 

 

Summary Sheet

Groundwater Body Code

Groundwater Body Name

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MT001

Malta Main Mean Sea Level

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MT002

Rabat-Dingli Perched

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MT003

Mgarr-Wardija Perched

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MT005

Pwales Coastal

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MT006

Mizieb Mean Sea Level

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MT008

Mellieha Perched

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MT009

Mellieha Coastal

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MT010

Marfa Coastal

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MT011

Mqabba-Zurrieq Perched

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MT012

Comino Mean Sea Level

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MT013

Gozo Mean Sea Level

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MT014

Ghajnsielem Perched

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MT015

Nadur Perched

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MT016

Xaghra Perched

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MT017

Zebbug Perched

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MT018

Victoria-Kercem Perched