# Hydro-Economic Mapping of Groundwater Potential in the Kunene and Omusati Regions, Namibia

Alexis Gutierrez, Alexandre Brugeron, Arnaud Soulignac, Laurence Gourcy, Sakeus Ihemba

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## To cite this version:

Alexis Gutierrez, Alexandre Brugeron, Arnaud Soulignac, Laurence Gourcy, Sakeus Ihemba. Hydro-Economic Mapping of Groundwater Potential in the Kunene and Omusati Regions, Namibia. Aquifer Characterisation and Management - Techniques and Perspectives [Working Title], IntechOpen, 2026, 10.5772/intechopen.1014115. [https://doi.org/10.5772/intechopen.1014115](https://doi.org/10.5772/intechopen.1014115)

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Submitted on 10 Feb 2026

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# Hydro-Economic Mapping of Groundwater Potential in the Kunene and Omusati Regions, Namibia

Alexis Gutierrez, Alexandre Brugeron, Arnaud Soulignac, Laurence Gourcy and Sakeus Ihemba

## Abstract

This study focuses on mapping groundwater potential in Namibia's Kunene and Omusati regions that face severe water scarcity due to arid conditions and limited surface water. The research integrates hydrogeological data, water quality assessments, recharge projections, and economic feasibility to create a spatial framework for sustainable water resource planning. Kunene, dominated by hard rocks, has limited aquifer potential, while Omusati, part of the Cuvelai-Etosha Basin, contains thicker sedimentary aquifers but suffers from poor groundwater quality, particularly high salinity and nitrate levels. A revised 1:250,000-scale aquifer potential map was developed using geological data, borehole yields from the GROWAS II database, recent studies, and fieldwork. Water quality was analyzed using major ions, fluoride, nitrate, and salinity, with a Water Quality Index (WQI) identifying high-risk areas. Sustainable groundwater yield and aquifer potential were assessed, incorporating climate change projections that indicate future declines in recharge, especially in Omusati and southeastern Kunene. Demand projections for urban and rural areas were combined with infrastructure cost estimates to assess the economic feasibility. The resulting water-resource opportunity map highlights areas where groundwater or surface water is viable, emphasizing the challenges faced by urban centers like Opuwo and Khorixas. While rural areas generally remain resource-positive due to low demand, the study underscores the need for site-specific investigations and improved data quality to support long-term planning in this water-stressed region.

**Keywords:** groundwater potential, water quality, sustainable yield, climate change, opportunity map, Namibia

## 1. Introduction

Namibia is one of the driest places of the planet. In northwestern Namibia, Kunene and Omusati are two climatically and hydrogeologically contrasted regions whose
population is facing water scarcity (Figure 1). There are no perennial rivers except the Kunene river at the border with Angola. Kunene is dominated by hard rocks and Neoproterozoic carbonate series with generally low aquifer potential controlled by fracturing; Omusati lies on the western rim of the Cuvelai–Etosha sedimentary basin with thick Cenozoic Kalahari sequences. Despite the presence of a major aquifer system in Omusati, groundwater is widely unsuitable for human consumption, and bulk water supply is provided through the Calueque dam in Angola through the Etaka canal and associated surface water networks. The demographic growth of local ethnic groups, the perspective of mining development, and the threatening of climate change underpin the need for spatially explicit planning of water resources.

In Namibia, anticipation of drought situations can be considered as major decision-making factor. The need for sound hydrological criteria to anticipate crisis is crucial. The government has declared several times (2012, 2016, 2019, and 2024) a state of emergency on the account of the persisting national disaster of drought.

The climatic regional context is prone to severe drought crisis [1]. Aridity classification based on the precipitation over potential evapotranspiration (P/PET) ratio [2] places most of the area in arid zones. These features compound existing development pressures linked to demographic growth and emerging economic activities, thereby raising water-security challenges that the present study seeks to address.

Knowledge of the aquifers in Northwest Namibia remains very limited and incomplete, due to the low density of borehole description and the small number of studies conducted in this area. Indeed, previous works in the Cuvelai-Etosha Basin (CEB) have focused primarily (i) on the southern edge of the basin, in the mountainous

<figure><img src="image_3.png" /><figcaption>Figure 1.
*Study area.*</figcaption></figure>
Otavi region [3, 4] and (ii) the central part [5] or the Ohangwena area in the north-eastern part [6, 7]. However, few studies have been carried out in the Kunene and Omusati regions. The most prominent one dates back to the 1990s [8]. The recent PhD thesis of Soetaert [9] focuses on the hinge area between Otavi mountains and western CEB. More local and unpublished works have not been yet used in a synthetic study.

Moreover, groundwater mapping is common in hydrogeological studies including the SADC area but few of them include sustainability [10] and none include economic assessment.

This chapter presents a stepwise approach to tackle the above issues. First, an updated *aquifer potential map* is developed at 1:250,000, downscaling and revising the national 1:1,000,000 Hydrogeological Map [11–13] using the 1:250,000 geological maps [14] and multiple ancillary datasets [15, 16]. The GROWAS II database [16] was quality-checked against borehole completion reports, with corrections applied to reduce inconsistencies in initial yield values; expert interviews and a targeted field campaign further informed local updates.

Second, *water quality* constraints are compiled and mapped to screen areas where chemistry limits potable supply and/or irrigation suitability. Third, *sustainable groundwater resource (SGR)* is estimated by combining aquifer potential with present-day and projected recharge. Recharge computation and climate-change impacts rely on a companion study [17], with uncertainties linked to forcing data and the water-balance method explicitly considered.

Fourth, *water demand to 2050* was assessed for urban schemes and dispersed rural demand, and *infrastructure sizing and costing* were carried out to derive average costs of resource mobilization. Finally, a *spatialized multi-criteria assessment (SMCA)* integrates (i) water balance between demand and SGR, (ii) average mobilization cost, and (iii) quality constraints to produce a *water-resource opportunity map (2050 horizon)* that pre-screens where groundwater or surface water constitutes feasible options. The authors emphasize the decision-support role of this synthesis product and the need for site-specific studies before project appraisal.

In sum, this chapter delivers a coherent, map-based framework linking hydrogeological potential, recharge under current and future climates, water quality, demand growth, and economic feasibility to guide regional water-supply planning in Kunene and Omusati regions.

## 1.1 Study area

The study area comprises the Kunene and Omusati regions in north-western Namibia (Figure 1). Kunene occupies the country's north-west and is bounded by Angola to the north, the Skeleton Coast to the west, the ephemeral Hoanib River to the south, and the western rim of the Cuvelai-Etosha Basin (CEB) to the east. With the exception of the Kunene River, river systems are ephemeral; northern tributaries flow toward the Kunene, while most other basins drain westward to the Atlantic in the Kunene region and southward to the Etosha Pan in the Omusati region.

Kunene administrative region covers ~116,000 km² with a dissected relief of hills and valleys; the Kaokoveld (northern part) is more mountainous. Pastoral systems are prominent—Himba in Kaokoveld and Damara further south—alongside commercial farming in the south-eastern sector (administratively divided into Kunene North and Kunene South, with Opuwo, Khorixas, and Kamanjab as main centers).

Climatically, mean annual rainfall increases from ~50 mm in the west next to the skeleton coast to slightly over 300 mm in the east, along the Opuwo ridge with high
interannual variability and a rainy season limited to October–April [12]. Long-term climatic records are sparse.

Omusati (~26,500 km²) borders Angola to the north, Kunene to the south and west, and the Oshana/Ohangwena regions to the east and northeast. Situated on the western edge of the CEB, much of Omusati lacks perennial surface flow; the principal engineered surface-water feature is the Etaka Canal, supplied from the Kunene at Calueque. The canal may follow a former Kunene channel [15, 18]. Areas distant from the canal rely on groundwater. Near the Angolan border, a very low-gradient inland delta forms a dense network of interconnected depressions (“iishanas”) that convey ephemeral flows during the November–April rainy season; during extreme rainfall over the wider catchment, extensive flooding (“efundja”) links many iishanas [15, 18].

From a hydro-climatic standpoint, Omusati is the driest part of the CEB, with rainfall increasing west-to-east from ~300 to 450 mm yr⁻¹. Potential evapotranspiration is ~2300 mm yr⁻¹ [15], far exceeding precipitation; with P/PET < 0.2, the regional climate is classified as arid [2].

Ephemeral drainage dominates both regions, consistent with limited or absent baseflow contributions during dry periods documented from river-gauge time series. This hydrological regime implies strong dependence of surface water on rainfall events and underscores the importance of groundwater resource, rainfall harvesting, and engineered conveyance.

In Omusati (Cuvelai area), bulk supply is conveyed from Calueque Dam in Angola *via* the Calueque-Oshakati canal/pipeline network for treatment and distribution by the national water supply company (NamWater) and the Ministry of Agriculture, Water and Land Reform (MAWLR); areas outside the central network rely on bore-holes [19].

Spatial datasets used later in the study also characterize the regional hydro-environment. The Digital Atlas of Namibia, 2022 [15] compiles springs, pans, swamps, and lakes—showing numerous springs in western Kunene and widespread pans in the flatlands of the CEB—which inform the subsequent checks and updates of aquifer potential at 1:250,000 scale.

## 1.2 Geological context

Several landscape domains can be defined according to (i) the nature of the relief, (ii) the geology, and (iii) the drainage (Figure 2). A relatively steep escarpment separates the coastal plains in the west of the country from the highest continental plateaus in the east, where the elevation rises to more than 1500 m (Mont Grootberg is the highest point with 1645 m). The Kamanjab plateau, in the south, is composed of the oldest cratonic rock outcrops in the region. This area is relatively flat to gently undulating. The Karstveld reliefs are located in the eastern part of the Kunene region. They extend as a narrow, elevated margin bordering the south and west of the Owambo basin whose elevation, although lower than the Karstveld, remains above 1100 m. They represent the eastern part of the Kaoko mountain range and the Otavi mountain range. Calcretes cover most of these areas in most of the lower-relief zones. The Kalahari sands cover the Owambo basin.

These reliefs are the remains of two mountain ranges: the Kaoko Belt and the Damara Belt. The Kaoko Belt to the west, running NNW-SSE, extends as far as northern Angola. The Damara Belt, running NNE-SSW, stretches across the central part of Namibia and extends into northern Botswana. Further south, the Gariep Belt, the southern extension of the Damara Belt, reaches South Africa. This triple junction
<figure><img src="image_4.png" /><figcaption>**Figure 2.**
*Tectonostratigraphic zones of the Damara Orogen (from [14, 26]).*</figcaption></figure>

geometry resulted from the Neoproterozoic Damara Orogen, which belongs to the Pan-African Orogenic System [20]. The Kunene Region is mainly concerned by the Kaoko belt, divided into four tectono-stratigraphic zones, described by Miller [21]: the Western Kaoko Zone (WKZ), Central Kaoko Zone (CKZ), Eastern Kaoko Zone (EKZ), and Southern Kaoko Zone (SKZ).

The Eastern Kaoko Zone (EKZ) is the foreland, comprising upright-folded Neoproterozoic Damara Sequence shelf carbonates resting on the western margin of the Congo Craton, the Palaeoproterozoic Kamanjab Inlier in the south, and Epupa Metamorphic Complex in the north [20]. Its western margin is affected by the Sesfontein Thrust.

The Central Kaoko Zone (CKZ) evolves from lower greenschist facies metamorphic grade in the east to upper-amphibolite facies grade in the west. The western margin is delineated by the Purros Mylonite Zone (PMZ). It is a sub-vertical median shear zone running the entire length of the Kaoko Belt, from North to South (below the Etendeka Plateau).

The Western Kaoko Zone (WKZ) is predominantly composed of high metamorphic grade (amphibolite-to-granulite) and intruded by numerous granitoids. Strike-slip faults compartmentalize orogeny-parallel panels of distinctly metamorphic grade [20].

The oldest rocks in the region are Archean and Mesoproterozoic metamorphic intrusives dating from around 2.4–1.7 Ga. They outcrop mainly in the Epupa metamorphic complex to the northwest (granitic orthogneiss, paragneiss and minor mafic rocks), and in the Kamanjab Inlier. The bedrock is mainly granite and gneiss and is considered the southwestern margin of the Congo Craton [22].
The Damara sequence occupies the Neoproterozoic Era. It is subdivided in two sub-sequences, the Nosib and the Otavi groups. The Nosi Group is composed of syn-rift sedimentary series. This detritic sedimentation, filling graben and semi-graben may reach several thousands of meters in thickness [23]. The Otavi Group follows with an important carbonate platform (4000 m) divided in three sub-groups: (i) Ombombo, (ii) Abenab, and (iii) Tsumeb. These subgroups are separated by two major glacial events dating from the Cryogenian (between 800 and 570 Ma) giving the Chuos and Ghaub diamictites (glacial breccia). Some authors have hypothesized that the Earth was entirely frozen at this time, leading to the “Snowball-earth” theory [24].

Sedimentation continued with the deposits of the syn-tectonic clastic sediments of the Mulden Group, which rests on the Otavi dolomites. The Mulden molasse unit was deposited during the compression phase of the Damara orogeny. Its thickness increases toward the Owambo basin.

The Karoo sequence that followed bears witness to a major climate change during the Paleozoic era, around 300 Ma ago, with glacial tillite deposits of the Dwyka Formation along the valleys. Resting in a disconformable manner on the Karoo Formation, the Kalahari group, consisting of Tertiary deposit of sands, gravel calcrete, and clay formations, is not abundant in the Kunene region but extends largely in the Omusati region and the rest of the Owambo basin which is itself part of the Kalahari basin [25].

## 2. Aquifer potential mapping: Data, methods, and revisions

An up-to-date aquifer potential map was developed to match (i) the extent of Kunene and Omusati regions and (ii) the effective resolution of the best-available inputs. Aquifer potential is defined operationally as the capacity of a geological reservoir to deliver water by drilling, conditioned by its hydrodynamic properties. Subsequent modules (water quality and recharge) are integrated to assess sustainable groundwater resource.

The aquifer potential map has been based on the following documents:

i) *Hydrogeological map of Namibia, 1:1,000,000*. The national map (editions 2001, 2011, 2020) classifies rock bodies into porous aquifers, fractured/fissured/karst aquifers, and rock bodies with little groundwater potential, with sub-classes for high/moderate potential and for generally low vs. very low potential [11, 12, 27]. This dataset underpins the initial transposition to 1:250,000.

ii) *Geological map of Namibia, 1:1,000,000* [14], used to constrain lithology and contacts at national scale.

iii) *Geological sheets, 1:250,000* for all tiles covering the two regions [28, 29], supplied as harmonized digital layers; these control the geometry of aquifer units at the target scale.

iv) *Waterpoints* from the *Digital Atlas of Namibia* (2022), together with Atlas-derived surficial deposits [15]; these were used to refine local characterization. The Atlas also proposes yield classes per aquifer-potential category (>15; 3–15; 0.5–3; <0.5 m³/h), although the underlying method is not documented.

v) *GROWAS II* national groundwater database [16], operated by MAWLR since 2018; >6500 boreholes are inventoried in the two regions but entries are heterogeneous and often incomplete, necessitating quality control before use.
The methodology followed three main steps:

* Step 1—Downscaling the national aquifer potential to 1:250,000
  Geological polygons from the 1:250,000 sheets were intersected with the national hydrogeological and geological maps to produce elementary mapping units carrying attributes from both source scales. This preliminary map served as a working baseline for subsequent checks and updates.

* Step 2—Update based on GROWAS II (quality-checked yields)
  A first comparison of initial yields (as recorded in GROWAS II) against aquifer-potential classes showed the expected trend in medians but also many extreme outliers within low-potential units, pointing to issues in borehole coordinates and/or yield entries. To increase confidence, the team verified entries against borehole completion reports (where available). Of 431 boreholes checked, almost half had erroneous depth and/or yield entries; additional records exhibiting unrealistic values or missing critical fields were excluded (2979 removals), and a further 862 were dropped due to missing yield values. The filtered dataset (2705 boreholes) produced a more consistent relationship between aquifer-potential class and observed yields and led to a general narrowing of yield ranges across classes.

* Step 3—Additional materials (experts, field work, local studies)

Targeted expert interviews and a May 2022 field trip were used to ground-truth the mapping and to identify areas where the national map's vectorization was not fully supported locally. Several unpublished local studies informed revisions (e.g., Okanguati, Sesfontein, Otjitanga, Ongandjera). A key revision concerns the Etendeka volcanic complex: high spring density [15] and some significant bore-hole yields within zones originally classified as "very low potential," and plausible vertical connection with underlying eolian sandstones in the south, justified moving the boundary between "very low to low" and "low to locally moderate" westward along a north-south line of perennial springs passing Springbock Gate.

Aquifer potential is also evidenced by pumping tests when available. To characterize the hydrodynamic parameters, 73 wells with pumping-test data drawn from MAWLR (including a subset curated for a PhD dataset [9], NamWater schemes, and legacy reports (e.g. [8])) were reinterpreted using a specific software developed at BRGM [30]. Conceptual models (Theis, Hantush, Gringarten) were selected case-by-case from drawdown/recovery records; the storage coefficient could not be estimated reliably due to the absence of observation-well monitoring. The resulting transmissivities range from $10^{-6}$ to $10^{-2}$ m$^2$/s, with the best T values in Otavi Group dolostones and in calcretes; Kalahari sediments are variable; other hard rocks are generally low except where intersecting fractured zones.

The validation of the final aquifer-potential map (Figure 3) was carried out by comparing each sectors delineated with unique aquifer potential class to the 2705 verified or non-suspect yield values contained in the filtered GROWAS II database. The box plot analysis and the synthetic table based on this dataset are shown in Figure 4 and Table 1.

Looking at these data, moderate aquifer potential zones for porous or fissured/fractured formations show very similar ranges of yield. A real difference is observed for the "high aquifer potential" class between porous and fissured/fractured media.
<figure><img src="image_5.png" /><figcaption>**Figure 3.**
Aquifer potential map.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Figure 4.**
Box plot of a selection of verified/non-suspect yield values, from the GROWAS II database, for each aquifer potential class (Kunene/Omusati regions)—colors from the Figure 3.</figcaption></figure>

The porous formations show statistically much higher initial yield values, with half of the boreholes that support more than 12 m³/h. Conversely, fissured/fractured aquifers show only slightly higher yields than those of the “moderate aquifer potential” class.
<table><caption>**Table 1.**
Comparison of yield ranges per aquifer potential, after correction on the database and revision of the map.</caption><thead><tr><th rowspan="2">Classes of aquifer potential</th><th rowspan="2">Surface (km²)</th><th rowspan="2">Number of boreholes in GROWAS II filtered database</th><th rowspan="2">Mean area between 2 boreholes (km²)</th><th colspan="5">Initial yield values after map and database revision (m³/h)</th></tr><tr><th>Minimum</th><th>1st quartile</th><th>Median</th><th>3rd quartile</th><th>Maximum</th></tr></thead><tbody><tr><td>Porous aquifers/ high potential</td><td>1113</td><td>25</td><td>45</td><td>0.47</td><td>4.65</td><td>12.2</td><td>18.5</td><td>91</td></tr><tr><td>Porous aquifers/ moderate potential</td><td>24,460</td><td>307</td><td>80</td><td>0</td><td>1.85</td><td>5</td><td>9.1</td><td>100</td></tr><tr><td>Fractured, fissured or karstified aquifers/high potential</td><td>5522</td><td>270</td><td>20</td><td>0</td><td>2.7</td><td>5.6</td><td>13.6</td><td>82.1</td></tr><tr><td>Fractured, fissured or karstified aquifers/moderate potential</td><td>24,484</td><td>814</td><td>30</td><td>0</td><td>2</td><td>4.5</td><td>9.1</td><td>150</td></tr><tr><td>Rock bodies with little groundwater potential/ generally low to locally moderate potential</td><td>36,797</td><td>1125</td><td>33</td><td>0</td><td>1.3</td><td>2.7</td><td>5</td><td>110</td></tr><tr><td>Rock bodies with little groundwater potential/very low and limited potential</td><td>49,343</td><td>164</td><td>301</td><td>0</td><td>0.3</td><td>1.5</td><td>4.65</td><td>60</td></tr></tbody></table>

The final aquifer potential map for Kunene and Omusati regions integrates (i) the downscaled national classification, (ii) corrected/filterede borehole yields, and (iii) targeted expert/field and literature inputs.

### 3. Assessment of water quality

Groundwater-quality data were compiled from three primary sources: (i) GROWAS (MAWLR) extractions prepared for this project, (ii) Campaigns from NamWater (2013–2014), and (iii) a curated dataset assembled for a PhD study covering the western Cuvelai–Etosha basin [9]. The GROWAS extract comprises 535 analyses from 346 monitoring points in Omusati and 3780 analyses from 2663 points in Kunene. The Soetaert dataset contains 533 analyses from 356 points (after excluding 52 isotope-only samples) and was preferred where duplicates with GROWAS existed due to the author's internal QA/QC [9]. A subset of NamWater samples lacked national IDs and/or coordinates and was therefore used for statistical treatment but not for spatial mapping.
For interpretation, the derived indices (e.g., Langelier, Ryznar) and trace elements with sparse coverage or values below quantification (e.g., B, Cd, Pb, Se, U) were excluded. The retained parameters include major ions, EC, TDS, NO₃⁻, and F⁻, which offer the most consistent regional coverage for hydrochemical diagnosis.

Bivariate plots and standard hydrochemical diagrams (Piper/Chadah) were used to diagnose dominant processes. Cross-plots indicate carbonate weathering control on Ca-HCO₃ and (Ca + Mg)-HCO₃ relationships, variable salinity coupled with Na enrichment, and evidence of cation exchange (e.g., trends in (Ca + Mg)-(HCO₃ + SO₄) vs. (Na + K)-Cl). The Chadah diagram (YX representation of Piper) highlights fields where irrigation salinity and residual sodium carbonate risks may occur; long-term irrigation concerns are expected when EC > 2000 µS cm⁻¹ or when Na dominates the cation budget, as seen for many Cl-Na-K-SO₄ and Cl-SO₄-Ca-Mg waters.

Key parameters were analyzed spatially. Maps of fluoride and nitrate (Figure 5) show extensive F⁻ occurrence consistent with geogenic sources and marked spatial heterogeneity of NO₃⁻, with strong local variability at the kilometer scale. Previous work in Namibia and the CEB reported elevated fluoride in similar geological contexts [31–34]. Gypsum influence is identified where SO₄ > 20 meq L⁻¹ in Ca-Mg-CO₃ waters (mapped “gypsum formation” influence), while a high (Ca + Mg)/(Na + K) ratio flags carbonate control; these spatial indicators align with Quaternary calcrete/gypsiferous units and dolostone/limestone belts.

A multi-parameter Water Quality Index (WQI) was computed from major ions and health-relevant elements, based on the guidelines for drinking water quality of the World Health Organization [35] and the Namibian Standards for the Evaluation of Drinking Water Quality for Human Consumption [36]. Resulting classes are ranged by chemical element from excellent to high-risk water. The WQI map (Figure 6) indicates that central Omusati largely exhibits poor potable quality (“high-risk water”), consistent with the elevated F⁻ and NO₃⁻; northern Kunene generally shows good quality, while the eastern Kunene sector is mixed, with better quality near granitoids, carbonates, and Quaternary sand/gravel/scree/calcrete.

Quality constraints were transposed onto the aquifer-potential map by delineating “high-risk water quality” polygons from WQI > 300 boreholes (Figure 7), complemented—where GROWAS II was sparse—by the national 1:1,000,000 “areas

<figure><img src="image_7.png" /><figcaption>**Figure 5.**
Spatial distribution of fluoride and nitrate concentration in groundwater.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 6.**
Spatial distribution of Water Quality Index (WQI) in Kunene and Omusati regions.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Figure 7.**
Aquifer potential map of Kunene and Omusati regions at the scale of 1:250,000, with high-risk water quality areas delimited.</figcaption></figure>
of saline groundwater.” The resulting overlay confirms widespread non-potable conditions in central Omusati (likely reflecting shallow resources typically tapped by boreholes), generally good quality in northern Kunene with local exceptions (Okanguati, Marienfluss), and identified problem areas in SE Kunene (Kheisian paragneiss/orthogneiss/granites and associated superficial deposits near Kamanjab–Fransfontein–Outjo; Ordovician biotite granites SW of Khorixas; Kuiseb/Okonguarri schists and micaschists at the southern border).

# 4. Assessment of sustainable groundwater resource

## 4.1 Methodology

Groundwater potential, derived from aquifer properties, expresses the aptitude of rocks and geological formations to deliver water. Groundwater potential map, however, does not take into account the sustainability of abstraction. A further step is thus to provide quantitative information on sustainable rates of groundwater abstraction.

The sustainable groundwater resource is defined as the minimum between (i) a safe fraction of the annual recharge and (ii) the intrinsic aquifer potential determined by the lithological properties and observed yields. In arid systems, sustainable yield must be considerably less than recharge to avoid adverse impacts on streams, springs, wetlands, and groundwater-dependent ecosystems [37]. For this study, 50% of the theoretical recharge is adopted as a safe yield to reflect uncertainty and spatio-temporal variability; the sustainable yield assigned to each location is therefore the minimum of “safe-recharge yield” and “aquifer-potential yield.”

Based on the quality-checked yield analysis (Chapter 3), the potential yields were assigned to each aquifer-potential class of the 1:250,000 hydrogeological map:

* Low to very low: $12 m^3 d^{-1}$ ($<0.5 m^3 h^{-1}$)

* Low to locally moderate: $42 m^3 d^{-1}$ ($0.5-3 m^3 h^{-1}$)

* Moderate (porous or fractured/fissured): $156 m^3 d^{-1}$ ($3-10 m^3 h^{-1}$)

* High (fractured/fissured): $240 m^3 d^{-1}$ ($>10 m^3 h^{-1}$)

* High (porous): $360 m^3 d^{-1}$ ($>15 m^3 h^{-1}$).

These values were applied to all polygons of the revised 1:250,000 map.

Recharge values [17] expressed in mm $a^{-1}$ for outcropping formations at 1:250,000 scale) were converted to $m^3 d^{-1}$ and divided by two to represent the “safe-recharge yield.” The sustainable yield used in mapping equals the minimum of this safe-recharge yield and the aquifer-potential yield.

## 4.2 Groundwater sustainable resource: Present situation

Combining the potential-yield layer and present-day recharge produces the present sustainable resource map (Figure 8). The western half of Kunene contains almost no sustainable resource owing to negligible recharge, except in the Etendeka complex (south of Sesfontein) and Marienfluss (the latter affected by water-quality concerns).
<figure><img src="image_10.png" /><figcaption>**Figure 8.**
Actual sustainable groundwater resource map of Kunene/Omusati regions.</figcaption></figure>

In contrast, the eastern half comprises reservoirs—surficial deposits, calcretes, dolostones, quartzites, gravels—capable of intermediate sustainable yields (≈4–10 m³ d⁻¹). Higher sustainable yields (>10 m³ d⁻¹) occur in SE Kunene north of Outjo (dolostone and surficial deposits) and in Damara-group dolostones around Opuwo, primarily reflecting higher recharge. In Omusati, the Cuvelai-Etosha Basin surficial deposits form a major reservoir currently capable of >10 m³ d⁻¹, but water-quality limitations are widespread in the central basin (see quality overlay on Figure 8).

### 4.3 Groundwater sustainable resource—Future projections

The mid-term (2041–2070) and long term (2071–2100) projections of sustainable resource is addressed through the difference map (Figure 9), which reveals spatially structured shifts. At mid-term increases appear north of Sesfontein, in Marienfluss, and to a lesser extent around Opuwo and parts of the far northern coast, consistent with slightly higher projected recharge there. Decreases of approximately 1–5 m³ d⁻¹ are observed across Omusati and SE Kunene (dolostone and calcrete aquifers) from Khorixas to north of Outjo.

At long term, a marked decline in sustainable resource is projected over much of the eastern half of the study area. Reductions of 1–5 m³ d⁻¹ affect central sectors (Opuwo, Sesfontein, Bergsig, Kamanjab, Khorixas), while declines >5 m³ d⁻¹ are projected in Omusati and north of Outjo.

These patterns are consistent with Caballero et al.'s findings [17] that highlight widespread decreases in potential recharge by the late twenty-first century, with mid-term increases deemed less robust due to climate-model uncertainty.
<figure><img src="image_11.png" /><figcaption>**Figure 9.**
Difference between present and future (period 2041–2070) situation for sustainable yield.</figcaption></figure>

**5. Water resource planning**

The study first delineated the supply configuration that prevailed in the area. The Central North Water Supply Area (CNWSA, “Cuvelai area”) relied on surface water abstracted at Calueque Dam (Angola) and conveyed through the Calueque–Oshakati canal and treatment works operated by NamWater, whereas the remainder of the study area—including most urban schemes in Kunene and south-western Omusati, and all rural settlements outside CNWSA—was supplied by groundwater (Figure 10). Ownership and operational responsibilities are split between NamWater and MAWLR, with frequent hand-overs after construction [19, 38].

The planning method integrated, on a 1 km² grid, the balance between local sustainable groundwater resource and requirements, the long-term average cost of mobilizing the additional 2050 needs, and a binary potability constraint derived from the water-quality screening. Demand was assessed for towns using the latest master plans and feasibility studies, and for rural areas using population density, institutional layers (schools, clinics), tourism facilities, and livestock carrying capacity. To align the design with NamWater practice, flows were sized on the average day in the peak month. Accordingly, the analysis defined the Average Annual Daily Demand (AADD), the Average Annual Daily Requirement (AADR = AADD + losses), and the requirement during the peak month (AADRPM = AADR × peak-month factor). In the absence of reliable metered peak data, a peak-month factor of 1.5 and 20 h/day pumping was used for design conversions (Figure 11). Losses were taken as 15% in CNWSA urban schemes and 7.5% in rural systems; elsewhere, urban losses between 5 and 23% were adopted according to scheme-specific sources [39–41].

The analysis time horizon was 2050, with no official demographic projections beyond 2042, long-term uncertainty rises rapidly thereafter, and 30-year horizons align with typical water-infrastructure lifecycles used for investment planning and TOTEX evaluation.

Population scenarios were compiled separately for Kunene and Omusati, for their relative urban and rural areas, and the resulting densities for 2011 and 2050 were mapped to support the spatialization of rural demand. The urban assessments assembled baseline demands and water-loss estimates from recent planning documents, projected them to 2050, and derived AADD and AADR time slices and the additional
<figure><img src="image_12.png" /><figcaption>**Figure 10.** Location of NamWater's Central North Water Supply Area and of urban schemes in the rest of the study area.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 11.** Water requirements in average and peak month (schematic representation). AADD = Average Annual Daily Demand; AADR = Average Annual Daily Requirements.</figcaption></figure>

AADRPM used for sizing of the technical components. For illustration, Outjo's AADR rose to 4736 m³/day by 2050 with an additional ADRPM of approximately 145 m³/hour (assuming 20-h pumping), and Khorixas reached an AADR of 4722 m³·d⁻¹ with an additional ADRPM of about 144 m³/h.

Rural requirements were derived from local consumption norms (current rural water demand = 25 l/capita/day, assumed to reach 43 in 2050), institutional inventories,
<figure><img src="image_14.png" /><figcaption>**Figure 12.**
*Water supply infrastructure design.*</figcaption></figure>

tourism facilities, and livestock water needs derived from carrying-capacity mapping [15, 18]. Following MAWLR practice, one rural water point was assumed to cover a service radius of 2.5 km ($\approx$20 km²), and the gridded calculations scaled the per-cell requirement accordingly. The approach produced current and 2050 AADD/AADR per rural-density class, together with additional AADR/AADRPM values used for infrastructure sizing.

Infrastructure elements were sized with a standard configuration that included a production borehole (150 mm diameter) drilled to the pump setting plus 3 m, a submersible pump sized against the additional AADRPM but capped by the local sustainable yield, a PN16 HDPE pressure pipeline up to the delivery node, and an elevated reservoir dimensioned as twice the additional AADR, with caps set at twice the sustainable yield (Figure 12).

Standard geometric definitions and the Hazen–Williams relation for head losses (HDPE, C = 150) were applied to compute dynamic heads. Pump selections were screened against a Grundfos table to cover heads of 50–250 m and flows of roughly 2–15 m³ h⁻¹. The design also included an elephant-proof fence and considered solar power for pumping. The costing adopted 2023 Namibian dollars (excluding VAT), counted drilling with depth-based regressions and standard accessories, used published pricings for pumps, and PN16 HDPE or PN16 uPVC, and included reservoirs and fencing. OPEX comprised power supply and routine maintenance. Installation overheads for clearing/ excavation and fittings were applied as 10 and 20%, respectively [19, 42]. Where solar pumping was feasible, the study tested scenarios with partial solar operation (e.g., 8 h d⁻¹) and recommended using water storage as the preferred energy buffer, with implications for reservoir sizing and operations. Stress tests with extreme input values and cost-share analysis showed that pipelines dominated CAPEX as distance increased, while power supply dominated OPEX across cases. The long-term average cost of groundwater mobilization at the 2050 horizon was then computed on the grid and mapped to reveal spatial cost patterns largely driven by economies of scale and depth/resource scarcity).

The spatialized multi-criteria assessment (SMCA) combined three indicators. First, a water-balance indicator measured the fraction of demand that the sustainable yield could cover, discretized into five classes from <10 to >100%. Second, an
average-cost indicator grouped the long-term costs into nine classes expressed in N$/m³. Third, a binary potability indicator masked areas where groundwater quality was unsuitable for human consumption. These indicators were aggregated using a hue-and-saturation matrix, where hue encoded the water balance and saturation encoded the cost, and where poor potability appeared as an overlay (Figure 13).

The algorithm proceeded in three steps:

Step 1 (Urban, present): distribute current AADR across the town's cells to map theoretical current balance (no cost).

Step 2 (Urban, 2050): compute balance and cost for additional 2050 needs; cells exceeding a cost ceiling of 52 N$/m³ are deemed uneconomic for the town and pass to Step 3.

Step 3 (Rural, 2050): compute balance + cost against the entire 2050 requirement for remaining cells. Overlay quality in a final pass.

The urban area of Outjo and its surrounding rural areas make a perfect example to understand how the three steps of the simulation algorithm color the map (Figure 14), and how it should be interpreted.

1. *Current theoretical water balance of Outjo:* The city's urban area appears in orange to black colors, meaning that the potential contribution of the aquifer to meet the needs is globally low.

2. *Water balance and average cost of future additional water mobilization for urban areas:* When examining additional future water needs, only two areas appeared capable of contributing significantly. These formed two parallel east-northeast-oriented strips following carbonate formations of the Damara/Otavi Group: the dolostone of the Elandshoek Formation and the marble-, dolostone-, and limestone-rich Karibib Formation, both identified as offering good yield potential in

<figure><img src="image_15.png" /><figcaption>**Figure 13.**
Color palette of water balance and average cost matrix.</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Figure 14.**
Three steps coloration of the grid cells, the example of Outjo urban area and its rural surroundings.</figcaption></figure>
the sustainable-resource analysis. Each cell within these zones could theoretically
supply less than 10% of the additional demand, and the progressive lightening
of the gray shading away from the urban center indicated that supply costs in-
creased with distance. In theory, several boreholes connected by a single transfer
pipeline along these strips could meet the total additional demand while reduc-
ing unit costs through shared infrastructure. However, such large-scale conclu-
sions require further site-specific studies, particularly to assess water quality.

3. Water balance and average cost of future additional water mobilization for rural areas: Most surrounding rural areas appeared in shades of green, indicating that future groundwater availability would exceed projected water requirements. This reflected very low population density and consequently low demand, even by 2050. In some locations, demand would remain so limited that developing new infrastructure would be economically unfeasible, as shown by the very light green cells, while white cells indicated an absence of exploitable resources. A few areas showed comparatively higher demand (darker green cells), driven mainly by non-domestic uses such as schools, clinics, or tourism facilities. In these cases, groundwater resources would still be sufficient to meet the future needs at an acceptable cost.

At the scale of the study area, the resulting opportunity map displayed coherent regional patterns (Figure 15). The western fringe, where resources were meager and demand sparse, rarely met projected needs at acceptable costs; eastward, most rural cells were resource-positive because requirements remained low, whereas urban opportunities were spatially concentrated and highly sensitive to distance-driven pipeline costs.

In the Cuvelai (CNWSA), the analysis reaffirmed the long-standing reliance on
surface water, given the widespread unsuitability of shallow groundwater for human

<figure><img src="image_17.png" /><figcaption>**Figure 15.**
Opportunity map for groundwater exploitation in Kunene and Omusati regions (legend is given in Figure 13).</figcaption></figure>
consumption. The study recalled the 1969 bilateral abstraction rule at Ruacana/Calueque (weekly abstraction limited to one-half of natural flow, capped at 6 m³/s) and reported that updated scenarios for 2050 yielded total abstractions of maximum 145.72 Mm³/y in the high-range scenario, well below the 189 Mm³/y cap. The Ruacana South Water Supply Project had, by 2022, evolved to include Opuwo, with stakeholders expressing a preference for piped surface water—perceived as cleaner and simpler to operate—over groundwater in areas with poor quality; the opportunity map converged with those findings by indicating limited local groundwater options for Opuwo and acceptable rural groundwater options in designated surrounding areas, subject to quality and cost variability [39, 43].

**6. Limits and uncertainties**

Most limitations arise from data availability and quality. The scarcity of direct measurements (recharge, pumping-test parameters, scheme performance, costs) forced the use of indirect estimates and empirical relations that are not unbiased. Access to recent reports and consistent datasets—particularly for the economic/costing component—was difficult; substantial effort went into identifying interlocutors and collecting fragmented information. GROWAS II data also contain numerous errors (coordinates, yields, depths); a detailed check of 431 completion reports indicated about one in two boreholes had erroneous entries, and the database is incomplete. These issues did not prevent the production of thematic maps, but they condition their use and interpretation.

**6.1 Aquifer potential map**

The 1:250,000 aquifer-potential map is a fair update and regional zoom of the national 1:1,000,000 hydrogeological map for Kunene and Omusati [12, 27]. However, it inherits an intrinsic limitation: the association of a geological unit with average aquifer properties. Heterogeneity in fracturing, weathering, facies changes, secondary fillings, and karstification cannot be represented explicitly; values are smoothed at unit scale. Consequently, the map must be read at its intended scale (1:250,000); it is not designed for site-specific decisions such as precise borehole siting or interpreting local anomalies in water quality.

**6.2 Water quality analysis**

The raw hydrochemical dataset required extensive pre-processing (reconstructing dates, identifiers, and coordinates). After cleaning, 3241 analyses out of >4300 were retained; exclusion (~25%) reflects the removal of undated, unlocated, and duplicate entries or analyses limited to isotopes [9]. Given the geological diversity and variable residence times, results are highly heterogeneous; therefore, no spatial interpolation was attempted. Instead, zones of poor overall quality were delimited, consistent with the national 1:1,000,000 hydrogeological map. Future trends in water quality were not assessed; geogenic constraints are assumed to persist, although anthropogenic contamination could increase with demographic and economic growth.

**6.3 Sustainable groundwater resource map**

The sustainable resource combines (i) aquifer-potential yields and (ii) recharge-derived safe yields, keeping the minimum of the two. Safe yield is taken as 50% of recharge—a pragmatic choice consistent with the need to leave water for dependent ecosystems [37]—after converting recharge from mm a⁻¹ to m³ d⁻¹. This discrete,
1 km²-mesh approach is classical where numerical models are unavailable, but remains theoretical and sensitive to the 50% coefficient, which may vary by hydro-system context. Climate-driven recharge projections carry large uncertainties; mid-term increases are less robust than long-term decreases in the study area [17].

## 6.4 Water-resource exploitation opportunity assessment

Demographic projections are uncertain and path-dependent. Water availability can increase an area's attractiveness; overestimating future requirements risks a self-fulfilling draw of people to newly supplied zones. Conversely, water scarcity can depress local growth and induce migration. Limited, outdated information on schools and clinics adds uncertainty to institutional demand estimates.

More recent and accurate technical data on existing schemes would improve the sizing of additional 2050 infrastructure. In the absence of an updated asset inventory or master plan, several scheme parameters had to be approximated.

Cost functions were built from the literature, supplier catalogs, and requested quotes; they are fit-for-purpose at regional scale but should be refined with NamWater/DWSSC through a shared country-wide water observatory of techniques and costs. The analysis excludes historical costs that still weigh on infrastructures and omits grid-connection CAPEX (data gap). Pipelines dominate CAPEX as distances grow; power supply dominates OPEX. A high-inflation, import-dependent context (equipment sourced overseas or from South Africa) adds price-escalation risk [19, 42].

Treatment of highly mineralized water was not included in cost estimates. In practice, advanced treatment is financially inaccessible for most rural settings; past RO attempts in Omusati failed (spare parts, staffing, high salinity, and hardness/ brine disposal). Opuwo has treatment in place but not operating at its best; Khorixas has been studied [40]. Case-by-case assessments are required.

Recharge was computed as potential recharge on mapped aquifer formations, implicitly assuming spatially distributed infiltration; this is more defensible in sedimentary settings than in basement/mountainous areas where hydrosystems are discontinuous. The 1-km² cell improves comparability but can misrepresent local lineament/ valley-controlled aquifers; drilling off these paths often results in dry wells [17].

Environmental flows were not included. Reasons are: (i) the only perennial river (Kunene) is mainly exogenous to the study area; (ii) no reserved flows for springs/wetlands exist in current regulation; (iii) data are lacking on the thousands of springs, and boreholes for wildlife in parks/conservancies are not inventoried or monitored. This represents a critical knowledge gap. A first step would be to inventory and add these wells to GROWAS.

There are no operating mines in Kunene/Omusati (at the time of the study, i.e., 2023), but 2868 mining claims and several exclusive prospecting licenses exist; environmental impact assessment documents for projects in the Opuwo Copper-Cobalt area envisage large process-water needs (e.g., ~4.5 Mm³ y⁻¹) potentially from ground-water, a dam, or a pipeline [44]. Actual timelines and volumes are not yet known/ communicated; thus, industrial demand could rapidly become significant but was not integrated quantitatively.

## 6.5 Impact of uncertainties

These uncertainties do not undermine the relevance of the results, because the outputs produced in this study are intentionally positioned at the earliest stage of the
planning process. The opportunity map is a strategic screening tool: it identifies broad
zones where groundwater development is plausible, marginal, or highly constrained, and
it helps focus on future investigations where they are most needed. It is not intended to
replace feasibility studies, pumping tests, or detailed engineering design, which remain
indispensable before mobilizing new resources. Instead, it provides a coherent framework
that structures subsequent work, reduces exploratory costs, and improves the targeting of
site-specific assessments. The intermediate products (aquifer potential revision, quality
screening, sustainable yield estimation, and cost assessment) are also directly usable by
planners to shape master plans or guide more detailed project preparation. This hierarchi-
cal approach ensures that, even with uncertainty, the findings remain fit for purpose.

7. Conclusions and perspectives

This study delivers a stepwise, map-based framework that links aquifer potential, pres-
ent and future recharge, water quality constraints, and the economics of supply to support
groundwater planning in Kunene and Omusati at the 2050 horizon. The combination of
(i) a revised 1:250,000 aquifer-potential map, (ii) recharge-based sustainable yield, (iii)
demand projections and engineering sizing, and (iv) long-term average cost produced a
water-resource opportunity map for pre-screening groundwater vs. surface water options.

Recharge is intrinsically low in this arid context: Over 1991–2020, it averages
1% of rainfall in Kunene and 4% in Omusati regions, as established in the project’s
companion recharge study [17]. Mid-century projections suggest slight increases in
the north-west of Kunene and decreases of comparable magnitude in the south-east
and Omusati, followed by a general decrease by ~2080, albeit with large uncertainties
typical of climate models.

At regional scale, the western fringe is both resource-poor and sparsely popu-
lated; where local demand spikes, costs are high, and the resource rarely meets
projected needs. Further east, rural areas are generally resource-positive in 2050
because requirements remain low, whereas most urban areas—notably Ombika,
Khorixas, Fransfontein, Sesfontein, Anker, Terrace Bay, and to a lesser extent Bergsig,
Okanguati, Opuwo, Otjovasandu, Outjo, Erwee, Kamanjab—face severe groundwater
challenges. In the Cuvelai (Omusati), groundwater is widely unsuitable for human
consumption; supply therefore hinges on surface water from the Kunene conveyed by
existing networks. Unless a deep fresh resource beneath Kalahari formations is identi-
fied (not investigated here), Omusati and the eastern part of Kunene (incl. Opuwo)
will continue to depend on new or expanded surface water schemes [39, 43].

Overall, the opportunity map provides results consistent with the detailed project
appraisals (e.g., RSWSP) and is useful for pre-screening investment options; however,
site-specific studies remain necessary for design and appraisal of any given project.

The methodology is experimental and innovative and can be improved at each
step. Priority actions identified in the study include:

* Improve raw data quality, particularly in GROWAS II (coordinate, depth, yield corrections);

• Update well inventories to document current abstraction and demand;

* Enhance monitoring with additional observation wells and automatic water-level recorders (telemetry);
* Undertake pumping tests and hydrogeological/hydrochemical investigations to refine local parameters;

* Assess environmental water demand to sustain springs and wetlands under population growth, tourism, and possible mining expansion.

In conclusion, the 2050 water-resource opportunity map offers a rigorous pre-screening tool to orient decisions at regional scale, while acknowledging (i) the low and spatially variable recharge that sets hard constraints and (ii) the data/uncertainty limits that necessitate local feasibility studies—especially in quality-constrained areas and around urban centers where costs and deficits are most acute.

## Acknowledgements

The authors wish to express their sincere gratitude to the French Development Agency (AFD) for financing this study under a tripartite agreement with the Ministry of Agriculture, Water and Land Reform (MAWLR) and the Ministry of Environment, Tourism and Forestry (METF) of Namibia. The authors also extend their appreciation to the staff of both ministries who contributed to the study, in particular, Ms. Maria Amakali, Director of the Directorate of Water Resource Management at MAWLR; Mr. Bertram Swartz, former Deputy Director of the Geohydrology Division at MAWLR; and Ms. Anna David, Senior Hydrogeologist at MAWLR.

## Conflict of interest

The authors declare no conflict of interest.

## Author details

Alexis Gutierrez¹*, Alexandre Brugeron¹, Arnaud Soulignac², Laurence Gourcy¹ and Sakeus Ihemba³

1 BRGM, Orléans, France

2 ECORESIL, Montpellier, France

3 MAWLR, Windhoek, Namibia

*Address all correspondence to: a.gutierrez@brgm.fr

## IntechOpen

© 2026 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. [CC BY](https://creativecommons.org/licenses/by/4.0)
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