TANO BASIN

The Tano Basin is a transboundary river basin shared between Ghana and Côte d’Ivoire, and it forms one of the four principal basins within Ghana’s southwestern river system—alongside the Ankobra, Bia, and Pra basins.

Geographically, the basin lies between latitudes 5°00’ N and 7°40’ N, and longitudes 1°48’ W and 3°05’ W, covering the western-northern part of Ghana. The total area of the basin is approximately 16,060 km², with about 92.6% (14,875 km²) located within Ghana and the remaining 7.4% (1,185 km²) extending into Côte d’Ivoire.

Topography and Elevation

The upstream areas of the basin consist of highlands, with average elevations around 540 metres above sea level, particularly near the Boyem Mountain Ranges in the Bono East Region. The middle sections of the basin drop to about 225 metres, while the southern areas are much flatter, ranging between 0 and 15 metres, with an average elevation of 50 metres above sea level.

The Tano River System

The Tano River, the basin’s main watercourse, stretches approximately 512 km in length. It originates from the Boyem Mountain Ranges near Techiman and flows southwestward, ultimately discharging into the Ehy/Tano/Aby Lagoon complex, which straddles the border between Ghana and Côte d’Ivoire. Notably, most of this lagoon system lies within Côte d’Ivoire.

The basin’s drainage network is well-developed and includes the Tano River and nine major tributaries, creating a drainage density of 0.032 km²/km. This interconnected system plays a vital role in supporting local ecosystems, agriculture, and livelihoods within the basin area.

Sub Basins

The major tributaries of the Tano River are the Boin (821 km² of which 655 km² is in Ghana), Disue (1,715 km² of which 1,709 km² is in Ghana), Amama (958 km²), Abu (1,650 km²), Gaw (984 km²), Suraw (640 km²), Samre (487 km²), Totua 440 km²), and Disri (370km²).

Geological Overview of the Tano Basin

The Tano Basin lies within Ghana’s extensive Precambrian basement complex, primarily composed of crystalline igneous and metamorphic rocks. The landscape is largely underlain by metamorphosed and folded rocks belonging to the Birimian system, which plays a key role in the region’s geological structure.

The main geological formations within the Basin and their areal distribution are as follows:

Granite (Granitoids) – 38.1% (dominant)
Birimian Sediments – 31.9%
Birimian Volcanics – 25.5%
Eocene & Cretaceous Sedimentary Rocks – 2.1%
Upper Voltaian (Kwahu Group) – 1.8%
Tarkwaian Rocks – 0.6% (least dominant)

Birimian Formation

The Birimian series includes slates, phyllites, greywackes, tuffs, and minor lava flows. These rocks are strongly folded, foliated, and jointed, with significant weathering along fractures and weak zones that can promote water infiltration and groundwater movement.

Tarkwaian Formation

The Tarkwaian rocks, although less extensive, are slightly metamorphosed and folded, with some open joint systems that may support limited groundwater storage and movement.

Upper Voltaian (Kwahu Group)

Located in the northern part of the Basin, the Upper Voltaian is recognized as the thickest and coarsest formation in that region. Its structure and composition influence groundwater occurrence in that section.

Coastal Sedimentary Formations

In the coastal areas, the geology transitions to Cretaceous and Eocene sedimentary rocks. These formations feature a variety of rock types, including sand, clay, fossiliferous sandy limestone, marl, sandstone, siltstone, mudstone, shale, and basal conglomerates. Some of the limestone layers in this sequence are believed to have oil and gas potential, adding economic interest to this part of the Basin.

Administrative Structure

Administratively, the Tano Basin is made up of 6 administrative regions and 29 District and Municipal Assemblies. Approximately 40% of the Basin is covered by the Western North Region, 25% is within the Ahafo Region, the Ashanti Region takes 15%, 10% is in the Western Region, 8% is covered by the Bono Region, and the remaining 2% is within the Bono East Region. Out of the 29 districts, 6 each are in the Ashanti, Ahafo, and Western North Regions, 5 in the Bono Region, 4 in the Western Region, and 2 in the Bono East Region.

Demographic Features

Based on the 2021 Population and Housing Census, the estimated population within the Basin stands at 1,969,825. Of this, approximately 54% live in urban communities (defined as settlements with populations over 5,000), while 46% reside in rural areas.

Population estimates were derived by applying the proportion of each district’s land area that lies within the Basin to its total population. This approach provides a more accurate picture of the population distribution across the Basin.

While Tano North and Asutifi South districts are almost entirely located within the Basin, the remaining districts only partially fall within it. Internal migration has played a significant role in shaping the Basin’s urban population. Urban centres such as Techiman and Sunyani have become major attraction hubs for migrants due to increased economic opportunities and development. This urbanization trend is expected to continue, particularly impacting municipalities like Sunyani and Techiman, as well as emerging regional capitals such as Goaso and Sefwi Wiawso.

The average population density across the Basin is approximately 130 persons per square kilometre (pop/km²), closely aligning with the national average of 129 pop/km². However, density varies significantly within the Basin. Rural districts like Aowin record much lower densities (around 50 pop/km²), while urbanized areas such as Techiman Municipal report much higher densities (up to 716 pop/km²), often placing pressure on available infrastructure and services due to increased migration and rapid urban growth.

Socio-Economic Activities in the Tano Basin

The Tano Basin supports diverse socio-economic activities, providing livelihoods through agriculture, forestry, tourism, and mining.

Agriculture is the primary occupation for over 27% of the population (47% in rural areas). Both commercial and subsistence farming are practiced, with cocoa being the dominant cash crop—contributing 70–100% of income for cocoa farming households.
Other major crops include oil palm, rubber, coffee, copra, plantain, cassava, and coconut (especially along the coast). Irrigation and fishing practices remain largely traditional and limited in scale.
The Basin is rich in mineral resources, particularly gold, which is extensively mined in Kenyase, Bibiani, and Sefwi-Surano. However, illegal mining is widespread and contributes significantly to water pollution.
Logging and timber processing are major industries in forested areas, with operations in towns like Berekum, Goaso, Mim, Sefwi-Wiawso, and Samreboi. Non-Timber Forest Products (NTFPs) from community forests provide up to 35% of farmers’ annual income.
Urban economies are more diversified, featuring trading, crafts, machine operation, and small-scale industries like carpentry, block making, soap manufacturing, and metalwork. Large market towns include Techiman, Sunyani, Goaso, and Sefwi Wiawso.
The basin is home to notable tourist attractions such as the Ankasa Resource Reserve and cultural heritage sites. It also hosts a significant population of forest elephants. However, human activities and climate change pose threats to these assets.
Oil and gas exploration in the lower Tano Basin began in 2012, contributing to the national economy and presenting opportunities for regional industrial growth.

Ecosystems in the Tano Basin

The Tano Basin is home to a diverse range of terrestrial and aquatic ecosystems, shaped by its climate and geography. These ecosystems provide vital ecosystem services that support the livelihoods of communities across the basin — including clean water, food, and energy.

Terrestrial Ecosystem

The basin’s terrestrial landscape is made up of:

Semi-deciduous dense forests
Dry dense forests and clear forests
Farmlands and degraded lands

These forest ecosystems play a critical role in regulating freshwater supply by supporting the natural flow, filtration, and quality of water. Notably, several forest reserves have been established to protect river headwaters, including:

Boin Tano Forest Reserve – headwaters of River Boin
Tano Suraw Forest Reserve – River Suraw
Tano Suhien Forest Reserve – River Suhien
Disue Forest Reserve – River Disue

The Tano Basin is an ecologically and economically vital region, supporting millions of people through agriculture, forestry, mining, tourism, and fisheries. Its rich terrestrial and aquatic ecosystems offer essential services such as water supply, biodiversity, and climate regulation. However, these ecosystems face growing threats from unsustainable land use practices, pollution, illegal mining, and invasive species.