Modeling Tools for the Foum El Oued Groundwater Aquifer under

Climate Changes Context: Geodatabase and Hydrological Model

Noura Ait Oubaha

, Mohamed Faouzi

, Abdelkader Larabi

and Mohamed Jalal El Hamidi

Regional Water Center of Maghreb, LAMERN, EMI, Mohamed V University in Rabat, Rabat-Morocco

Keywords: Water management, Foum El Oued aquifer, IT tools, Geodatabase /GIS, Hydrological model, groundwater

modeling.

Abstract: Water resources management in arid countries requires the provision of all the necessary decision support

tools, and implies taking into account the climate change component which becomes a structural reality. The

Foum El Oued aquifer is one of the important water resources reservoir in the Laâyoune region, in the south

of Morocco. It is facing the vulnerability problem to climate change, which is reflected in the fluctuating

aquifer recharge and the risk of seawater intrusion due to the mean sea level rise. Our work focuses on

effective groundwater modelling of this aquifer under a climate change context. In this paper we present

results of the IT (information technologies) tools developed for this project, such as a regional geodatabase

under a GIS environment and a hydrological model of the Saquia Al Hamra river floods, that mainly supply

the aquifer recharge, and which was not taken into account in the past. These two IT steps provide the

necessary inputs for the groundwater model which will be a key decision support system for the decision

makers in water resources management, especially for water supply of Laâyoune population and irrigation of

the Foum El Oued agriculture area.

1 INTRODUCTION

The Foum El Oued aquifer is an important water

resources reservoir in the Laâyoune province, located

in the west of the city on the coast of the Atlantic

Ocean. Groundwater is used to supply Laâyoune and

El Marsa cities with domestic and industrial water

and to irrigate an agriculture area (250 ha) in the

Foum El Oued plain. The main recharge of the Foum

El Oued groundwater comes from the Saquia Al

Hamra river floods, up to 90% (ABHSHOD, 2007),

that occur three to five years. In this aquifer,

groundwater has undergone significant pumping (6

Million m

in 2018 for drinkable water) confronted

with a low rainfall and irregular aquifer recharge

which has increased the risk of seawater intrusion

from the Atlantic Ocean (El Mokhtar et al., 2018).

Furthermore, climate change affects also the Foum El

Oued groundwater management ranging from

changes in recharge, increase of the mean sea level to

the increasing water demand on groundwater

pumping that leads to exacerbating the seawater

intrusion into the aquifer freshwater. The objective of

this research work is to develop a groundwater flow

and hydrodispersif model for the Foum El Oued

aquifer under the climate change context, with the

aim of being able to assess the impact of the various

groundwater abstractions on its potential as well as

the evolution of the seawater intrusion extend due

intensive pumping and increase of the mean sea level

rise. In order to develop these models, we need to

collect and process geological, climatic, hydrological,

hydrogeological and socioeconomic data on the study

area. Thus, a regional geodatabase is designed and

produced under a geographical Information System

(GIS) to allow data structuring, archiving and

interrogation. This geodatabase makes it possible to

produce various thematic maps and to provide the

necessary inputs for the mathematical model of

groundwater flow and seawater intrusion in the

aquifer.

The Foum El Oued groundwater aquifer is located

in the downstream of Saquia Al Hamra river, a long

non perennial river, that only flows during the flood

periods. These floods represent the main recharge of

the Foum El Oued aquifer. The last flood occurring

the October 2016 is the most important during these

50 years, recording a flow rate estimated to 3000 m

(ABHSHOD, 2007). After the passage of this flood,

significant increases of the piezometric level (more

than 3m) were recorded in several monitoring wells.

Hence, this situation motivated us to developed a

hydrological model for simulating this last flood, in

order to evaluate the possible future floods that could

occur in the river with the same return period that will

serve to assess future aquifer recharges.

In this paper, we focus on results obtained from

the two IT tools of both Database/GIS, including

climate change, and the HEC-HMS hydrological

model as applied to our case study, with the prospects

of exploiting these results for the preparation of

inputs and the development of future models on

groundwater flow and dispersive models in the

aquifer of the study area (under progress).

2 METHODOLOGY AND IT

BACKGROUND

2.1 IT Tools for Groundwater

Modelling

Groundwater modelling is the mathematical

representation of the flow system to solve the

equations that constitute the flow model (USGS,

2005). For the Foum El Oued groundwater model, we

are using several IT tools to process, produce and

interrogate data for the project. The main used tools

are the GIS, HEC-HMS and VISUAL MODFLOW

softwares. The GIS is a framework that we use for

gathering and processing data for the project and

producing thematic maps relevant to the aquifer

reservoir and the Saquia Al Hamra river basin.

Additionally, the GIS-geodatabase provided specific

data on climate change useful for hydrological and

groundwater modelling, including the conceptual

model. The HEC-HMS is used for the hydrologic

simulation of the last flood of the Saquia Al Hamra

river using regional data. The model will allow to

evaluate future flow in the specific basin. These tools

provide also the necessary inputs for the groundwater

model under Visual MODFLOW to simulate and

predict the groundwater flow conditions in terms of

quantity and quality.

2.2 IT for the Geodatabase

Groundwater modelling requires the

conceptualization of both the aquifer reservoir and

physical groundwater flow and solute transport. For

this purpose, we need to collect and process several

types of data on the study area. This is ensured by

developing a database to facilitate the organization,

processing and editing of the project data. Hence, we

developed a geodatabase under GIS; designed to store,

manipulate and interrogate geographic information

and spatial data. This geodatabase is a source of

geographic information, within a GIS, systematized

into geographic data sets built on top of relational

database management systems (RDBMS) such as

Microsoft Access, Oracle, or Microsoft SQL Server

that are customized for storing spatial data structures.

Data collected from several sources are digitalized

and geo-referenced; the spatial reference coordinate

system used for the representation and projection of

the geographic data in the study area is the WGS 1984

UTM Zone 28N.

These necessary data for the implementation of

the project were collected from national and regional

organizations involved in the water sector (Saquia Al

hamra and Oued Dahab Hydraulic Basin Agency

ABHSHOD, Laâyoune Regional Agriculture

Direction DRA, the National Office of Water and

Electricity-Water Branch / Direction of Saharan

provinces, the Regional Direction of Meteorology of

Laâyoune DMN, Mohammadia school of engineers

EMI, the Direction of Planning and Research of

Water DRPE). For different needs and data use,

processing of the collected data started by controlling

their homogenization and their format, as well as their

coherence, completeness and quality.

The project’s geodatabase is named “FEO_GDB”,

and it includes features, feature classes, feature data

sets, relationships and rasters. Features are spatial

vector objects (e.g., points, lines, polygons, and

multi-patches) with attributes (fields) to describe their

properties. The “FEO_GDB” is designed with a

thematic hierarchical architecture, including all

hydrogeological topics: geography, administration,

infrastructure, geology, hydrogeology, hydrology,

water uses, models, seawater intrusion, and allowing

producing thematic maps (Figure 1).

Figure 1: The thematic structure of the geodatabase.

The FEO geodatabase is used all among our

project to prepare and interrogate data for each

project thematic, to produce inputs for the

groundwater model and to use the results from this

model to produce others outputs. The interaction

between the geodatabase and all the other project

steps is continuous and interactive (Figure 2).

Figure 2: Database objective’s organizational scheme.

2.3 Hydrological Modelling

The hydrological model is a mathematical

representation of the hydrological processes in a

watershed, such as the saquia Al Hamra river,

involving all the hydrologic cycle (rainfall,

evaporation, runoff, etc.).

Simulation of the last flood of the Saquia Al

Hamra river basin was made by applying the

Hydrologic Engineering Center’s Hydrologic

Modeling System HEC-HMS. It is designed to

simulate the rainfall-runoff processes of watershed

systems. The process used for our simulation is the

Soil conservation service (SCS) Curve Number (CN)

model that estimates the precipitation excess as a

function of cumulative precipitation, soil cover, land

use, and antecedent moisture, using the following

equation (1):

















(1)

where P

=accumulated precipitation in time t, P =

accumulated rainfall depth at time t, I

= initial loss,

and S= potential maximum retention.

We also use other processes, the Clark unit

hydrograph for the transformation and a

meteorological model for the weather data used for

the simulation. For this latter simulation, we used and

applied the inputs provided from the data collected

from the National Direction of Meteorology (for

rainfall) and the Direction of Research and Planning

of Water (for flow rates).

3 GEODATABASE/GIS

EXPLOITATION FOR SITE

CHARACTERIZATION

3.1 Site Location

The Foum El Oued coastal aquifer is located in

Laâyoune province, in the south of Morocco, 20 km

west of Laâyoune city (Figure 3). It is a fresh

groundwater system that supplies the Laâyoune city

with drinking water and irrigation of an agriculture

area extended on the Foum El Oued plain. The study

area is located in an arid zone with a severe water

scarcity, exacerbated with the climate change impact

and increasing water demand, due to the socio-

economic development of the Laâyoune region.

Drinking water supply is ensured by both the

Laâyoune seawater desalinization unit (2/3) and the

Foum El Oued fresh groundwater aquifer (1/3) from

a pumping well field.

Figure 3: The Foum El Oued coastal aquifer location.

3.2 Geological Context

The Foum El Oued aquifer corresponds to the units

from the permeable late Miocene to Plio-Quaternary

geological formations. It is formed of a fluvio-lake

sediment, composed of complex sedimentary,

detrital, biochemical and chemical alternations.

These formations lie on an impervious substratum

composed of clay sediments from late Cretaceous to

late Miocene (Figure 4).

Figure 4: Geological schematic section of the Foum El

Oued area (DRHS, 2003).

3.3 Climate Context (past)

The prevailing climate in the study area is of the

desert type and very influenced by oceanic effects.

The temperature variations recorded in Laâyoune

weather station shows that August is the hottest

month of the year, with a maximum average of 27.7

°C, and December is the coldest month with a

minimum temperature of 15.2°C. The rain is very rare

in the study area, the annual rainfall values, recorded

in the Laâyoune weather station, between 1976 and

2018, range from 155 mm recorded in 1989 to 10.7

mm recorded in 1992 with an average value of 54.89

mm (figure 5).

Figure 5: Evolution of annual rainfall at Laâyoune weather

station, 1976-2018.

3.4 Climate Change Projections

In order to assess climate change at the regional level,

and with the objective of taking them into account in

the analysis, we worked with the regional climate

models (RCMs), which are the most suitable for the

project, in particular those from RICCAR, specific to

the Arab region (ACSAD and ESCWA, 2017). Thus,

we examine the projections of the two parameters,

temperature and rainfall, extracted from several

regional climate models and choose the most

appropriate results for RCP4.5 (moderate) and

RCP8.5 (extreme) scenarios (figures 6 and 7). The

extracted projections are relevant to two main local

weather stations (namely Laâyoune and Smara)

which are located respectively in downstream and

upstream of the Saquia Al Hamra basin.

Figure 6: Temperature projections for Laâyoune and Smara

weather stations until 2100.

These two figures show a trend of increase in

temperatures for both weather stations and for both

scenarios. However, these projections predict more

increase in temperature values for the Smara weather

station, exceeding the maximum of the recorded

averages (24.4 °C).

The increase is obviously greater

for scenario RCP8.5 than that of RCP4.5, where

temperature will exceed 24 °C before 2050. The

temperature projections for Laâyoune station show

also an overall increasing trend in mean temperature,

but it is more marked for RCP 8.5 than for RCP4.5.

The projections of rainfall in Laâyoune station

indicate that for the RCP4.5 scenario there will be

increasing trend, which is unlike the prediction for the

north-eastern regions of Morocco where there will be

an overall decrease in the rainfall. While, the RCP8.5

scenario will expect a precipitation decrease in the

global trend (Figure 7). However, for Smara weather

Observedvalues

Projections

Observedvalues

Projections

station, the projections predict an increasing of

rainfall for both scenarios. This will result in a

positive impact on the Foum El Oued aquifer

recharge, as the main recharge comes from the Saquia

Al hamra river floods of upstream sub-basins

covering the Smara area (Figure 8).

Figure 7: Rainfall projections for Laâyoune and Smara

weather stations.

Figure 8: Saquia Al Hamra watershed and its sub-basins

3.5 Characteristics of the Hydrological

Basin

The Saquia El Hamra is the main river of the Sahara

watershed which crosses the whole basin in its

northern part from east to west and having its outlet in

the study area (Figure 8), where floods are spreaded

over the plain before reaching (very rarely) the

Atlantic Ocean. The river length is 400 km and the

watershed is extended on a total area of 82 000 km

The river is characterized by a wide bed which can

reach 2 to 3 km in some sections, and the flow occurs

during heavy floods from upstream sub-watersheds.

The hydrographic network of the watershed

includes many rivers, the most important ones are

those of the left bank of the stream; El Khatt, Boucraa,

Tizert, Target, etc. (Figure 8). Table 1 below provides

some characteristics of the Saquia Al hamra river.

Table.1. Saquia Al Hamra river characteristics.

Basin/sub

asin

Area

(

)

(

)

CC*

CT*

(

hours

)

Saquia Al

Hamra

82 000 2346 1,43 95

P*: Perimete

CC*: compactness coefficient

CT*: Concentration time

3.6 Hydrogeology of the Foum El Oued

Aquifer

3.6.1 The Aquifer Substratum and

Thickness

The aquifers lie uncomfortably on an impermeable

substratum composed of predominantly clay

sediments from the Upper Cretaceous to Upper

Miocene (silto-sandy clays and marls of gray, green,

blackish or whitish colors). This substratum is

shallow to sub-outcropping to the east of the Foum El

Oued area, few kilometers west of the town of

Laâyoune (Figure 10). Based on the elevation digital

model (DEM) and the substratum map, we could

produce the thickness map of the Foum El Oued

groundwater aquifer, which shows that the aquifer

thickness varies between 20m (east of the basin) to

190m along the Atlantic coast (Figure 9).

3.6.2 The Piezometric Fluctuations

The Foum El Oued groundwater table is monitored

since 1977 via a network of observation wells made

up of 32 piezometers, which do not show continuous

records of measurements over the time. Based on the

time series data collected from ABHSHOD for the

Foum El Oued aquifer, structured and processed in

the geodatabase, we were able to plot the piezometric

level evolution in observation wells as illustrated in

Figure 11. This latter clearly shows a decrease of the

groundwater level during 2011 due to operated

groundwater pumping by the National Office of

Drinking Water of Laâyoune (ONEE) and followed

by shutdown of some pumping wells. On the other

hand, we can clearly notice the groundwater level

increase during 2016 due to the Saquia Al hamra river

floods which have a positive impact on the

groundwater aquifer recharge.

Figure 9: The Foum El Oued aquifer thickness.

Figure 10: The Foum El Oued aquifer substratum.

Figure 11: Piezometric time series for a monitoring well

installed in the aquifer.

4 HYDROLOGICAL MODEL

4.1 The Saquia Al Hamra Floods

The hydrographic network of the watershed includes

many rivers and streams as illustrated by figure 8.

Surface water flow of the Saquia Al Hamra river is

controlled by a downstream dam, located just

upstream of the study area, and the only major dam

reservoir of the basin, with a storage capacity of 410

Million m

(Mm

). In the downstream of this dam, the

river’s bed is represented by large sand dunes at the

level of Foum El Oued aquifer, which contribute

favourably to the aquifer recharge.

The hydrological regime of the Saquia El Hamra

river is marked by a strong seasonal and inter-annual

irregularity. The maximum inflow occurs during

major floods from upstream sub-watersheds, when

the rainfall is very important in the upstream of Smara

region (Figure 12). The flood frequency of the Saquia

El Hamra river is about two to five years at Laâyoune

dam (Figure 13).

Figure 12: Historical floods of Saquia Al Hamra river

The last flood of October 2016 has recorded a pick

flow of 3000m

/s. This flood whose flow has caused

the rupture of the dam and carried away the dike, has

never been recorded before in the catchment.

Figure 13: The occurrence of Saquia Al Hamra floods

within the rainfall upstream (Smara) and downstream

(Laâyoune) of the basin.

4.2 Last Flood Simulation (2016)

The simulation is made by applying the Hydrologic

Engineering Center’s Hydrologic Modeling System

HEC-HMS. For this purpose, we used data collected

from the DMN and the observed flow rates of the

Saquia Al Hamra river at the level of Smara-Tantan

bridge, as recorded by the DRPE (DRPE, 2016). The

model was then calibrated in order to find out the

parameters allowing adjusting the observed values to

those obtained by simulation. Several parameters have

been calibrated such as the CN and the storage

coefficient. Figure 14 gives the preliminary results

obtained after several tests. These results will be

improved by the calibration and by introducing others

relevant parameters to the study area, and by using

other modeling tools taking into consideration the

topographic characteristics variation in the basin. The

modelling part is going on to improve these results and

to assess the aquifer recharge from floods as main

input in the groundwater flow model. The natural

aquifer recharge from precipitation for 2020 – 2100 is

already evaluated based on the DMN and RICCAR

time series of projected rainfall, but it would not be so

significant compared to the flood recharge (Larabi et

al. 2020).

Figure 14: Simulated results by HMS hydrological model.

5 CONCLUSION

The results of the IT tools developed for this project,

such as the regional geodatabase /GIS and the

hydrological model of the Saquia Al Hamra river

floods that mainly supply the aquifer recharge, and

which was not taken into account in the past, are of

great importance for developing the groundwater

models. The geodatabase and hydrological modelling

have led to important results on climate change,

hydrology and groundwater characterization for the

Foum El Oued aquifer and the Saquia Hamra river

basin. This helps also the decision maker to monitor,

control and mange water resources in the site.

Additionally, these two IT steps provide the

necessary inputs for the groundwater model which

will be a key decision support system for the decision

makers in water resources management, especially

for water supply of Laâyoune population, irrigation

of the Foum El Oued agriculture area and protection

of the aquifer from seawater intrusion. This

management should take into consideration the

climate change adaptation, especially when the

projections show positive evolution of the rainfall in

the upstream basin.

ACKNOWLEDGEMENT

Data collected for this project have been provided by

national organisations and the data for the climate

change projections have been provided by UN-

ESCWA-Beirut. We would like to thank them all for

their full support.

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