Sand and Gravel Aquifer

Contents:

1. Description of Water Resource

1.1. Geographical Description

1.2. Hydrological Description

1.3. Water Quality

2. Socioeconomic Issues

3. Transboundary Issues

 

1. Description of Water Resource

 

Aquifer_Map.jpg

 

1.1. Geographical Description

The Sand and Gravel Aquifer shared between Malawi and Zambia is an unconsolidated intergranular aquifer and weathered basement complex covering an area of 25,18km2.  The Government of Malawi recognises that delineation of the aquifer is difficult, and that the aquifer has not yet been delineated formally[1].

1.2. Hydrological Description

The predominant lithology of the aquifer is alluvium and weathered basement. It is characterised by a low to high primary porosity, with secondary porosity developed through fractures in the basement. It is also characterised by a low horizontal and a low to high vertical connectivity in the consolidated formations and generally a high horizontal and vertical connectivity. The transmissivity values on average are fairly low, ranging from 3 m2 per day to 26m2 per day.  The aquifer receives the bulk of its recharge from precipitation.

The aquifer is also characterised by outcrops of metamorphic rocks at the boundary with Zambia and within Malawi. The aquifer is considered a single layer, confined system. Importantly, the recharge areas of aquifer are on the border of the two countries and they need to be protected.

About 4% of the aquifer in Malawi is covered with groundwater dependent ecosystems.

The mean annual rainfall in the area covered by the aquifer ranges from 800 – 1200 mm per annum on average. The average yield in the weathered zone of the basement complex lies in the range of 1 to 3 litres per second.

Mean annual recharge in Zambia is 20.4 mm3/ annum. Mean annual recharge in Malawi is estimated to be over 2000 mm3/ annum. This difference in recharge is largely due to the weathered basement in Malawi that forms an integral part of the system. The combined recharge area is approximated at 15,500 km2 and the discharge mechanism is through groundwater flow into surrounding aquifers and through river base flow.

 

Physical Characteristics of the Sand and

Aquifer Size (km2)

25,318

Maximum depth (m)

40

Mean depth (m)

30

 

1.3. Water Quality

The quality of groundwater is generally of good quality, with only 1% of the aquifer in Malawi unsuitable for consumption despite high salinity in the superficial layers. The amount of groundwater that is unpalatable is 5% in Zambia. There are notably high iron concentrations in some areas of the aquifer that make it unfit for consumption. There aquifer is facing nitrate challenges as well as excess fluoride which is a problem within particular areas of the shared resource.

As a result of agricultural and household practises, there is some pollution that is experienced in the aquifer ranging from 1% to 5% in Malawi and Zambia.

2. Socioeconomic Issues

The aquifer supports rural domestic water supply and provides otherwise limited protected and safe potable water. Abstraction of water from the Zambia side amounts to 10Mm3, while it is 237Mm3 annually on the Malawian side.

3. Regional Developments in Transboundary Groundwater Management

The current SADC Regional Strategic Action Programme (RSAP III) has a Groundwater Management Programme of Action, focusing on:

(1) policy and institutional frameworks;

(2) transboundary aquifer management;

(3) awareness raising; and

(4) regional cooperation over groundwater management. 

 In support of this program, the World Bank approved a “Sustainable Groundwater Management in SADC Member States” project in 2014, aimed at:

(1) operationalization of the SADC Groundwater Management Institute;

(2)  strengthening institutional capacity for the sustainable management of groundwater in SADC;

(3) advancing knowledge on national and transboundary groundwater; and

(4) promoting groundwater infrastructure management and development. 

This work will be implemented by the SADC Water Division with inputs from Member States through the establishment of national focal points.  As such, this project offers an opportunity for Malawi to capitalize on existing momentum to develop its knowledge base and begin to establish cooperative management mechanisms for its shared aquifer. 

With respect to legal frameworks, both the (revised) SADC Protocol on Shared Watercourses and the ZAMCOM Agreement (2004) incorporate shared groundwater as part of their definition of “shared watercourses.”  The shared aquifer would this fall under the ambit of the integrated planning within the Zambezi Basin and be subject to all of the requirements of joint management and planning under both of these treaties.

4. Transboundary Issues

There are currently no transboundary agreements between Malawi and Zambia, but an agreement with limited scope is under preparation to address the challenges facing the shared aquifer.  There exists potential for cross-border flow taking place and assessments show that there is relatively high use of this flow, relative to the mean annual recharge. An issue of concern is the possibility of high localised pollution as the cross-border region is quite densely populated.

In light of the non-existence of transboundary legal instruments for managing, utilising and conserving the aquifer, it is recommended that:

  1. Transboundary groundwater data sharing, archiving and monitoring need to be in place for better management of the shared aquifer. To this end, multi-country research on the basement aquifer is necessary to promote sharing of knowledge between research establishments and water management institutions.
  2. The two states need to negotiate and implement the necessary agreements. This might also entail crafting and introducing specific regulations in order to monitor the exploitation of the aquifer.

 

Relevant Documents

  • SADC Regional Strategic Action Programme
  • SADC Protocol on Shared Watercourses

 


[1] Transboundary Waters Assessment Programme (TWAP) 2014 Assessment of Transboundary Aquifers of Southern and Eastern Africa. Proceedings of a Regional Workshop 4-6 March, 2014, Nairobi, Kenya.