5. Real Islands

Let us now turn to real islands. This page is regularly updated when new islands are included and also when new data enable to strengthen the modeling and predictions

Last modification 2026-04-23

5.1. Summary table

Parameters used and water balance obtained

Island

R (\(m/d\))

K (\(m/d\))

por

\(h_{moy}\ (m. asl)\)

Volume (\(m^3\))

Surface (\(m^2\))

Recharge (\(m^3/yr\))

Avatoru

0.000828

8

0.25

0.15

1.33e6

8.73e5

2.64e5

Petite Terre

0.000548

3.456000

0.30

15.11e6

10.48e6

2.97e6

5.2. Avatoru Motu in Rangiroa (Polynésie Française)

5.2.1. Parameters

#IslandLens Param
sub_sampling = 3
clockwise = True
ttype = 'pq33a1000'
R = 0.000827698# m/j
por=0.25
motu = 864
K= 8
por=0.25
fi = 2*R*25/K/1025

islands="Avatoru"

fname = "./IslandsLib/data/Contours/Pacific/Polynesie/Rangiroa/Rangirao_%s.txt" % (motu)

u, Th, X, Y, Z, dx, dy, itp = il.IslandLens( islands, fname, ttype, fi, sub_sampling , clockwise, lakes=None, plot=False)

il.IslandBalance(islands,Z,dx,dy,R,K,por)

5.2.2. Results

  • Values for \(R\) and \(K\) were obtained from the meteorologic station of the airport and from the BRGM study of Rangiroa.

  • One piezometer exists on the islands and the average height of the water table coincides with the reconstruction obtained.

_images/Avatoru.svg

5.3. Petite Terre and Lake Dziani (Mayotte)

Lake Dziani is a hyper saline volcanic lake located north of the island its level on average is 0.

5.3.1. Parameters

import matplotlib.pyplot as plt

import IslandsLib as il

#####################
# Set arguments
#####################

# Name of Island and path to contour
islands = 'Petite Terre'
island_fname = "../data/Contours/Indian/Mayotte/Mayotte_Petite_Terre.txt"

# Name of lake and path to contour
lake = "Dziani"
lake_fname = "../data/Contours/Indian/Mayotte/Mayotte_Petite_Terre_dziani.txt"


lakes = [[lake, lake_fname, 0]] # list of lakes with file name and elevation of lake (masl)

#sub sampling
sub_sampling = 9

#clockwise
clockwise = True

# Triangulation settings
ttype = 'pq33a10000'

# Parameters
# Infiltration
R = 1. / (365.25) * (1-0.8) #m/d
#Conductivity
K = 4e-5*86400 # m/d
# Porosity
por = 0.3


fi = 2 * R * 25 / K / 1025

5.3.2. Results

The form of the lens is given in figure Modeled water table of Petite Terre island in Mayotte. For a discussion on the shape of the water table and comparison with existing measurements see Métivier et al. [2024] (spoiler: it seems to work :))

_images/Petite_Terre.svg

Modeled water table of Petite Terre island in Mayotte