Land cover of Mauritius Island.

In this digital era, high-resolution imagery offers a rapid and inexpensive means of monitoring land use changes. Digitally monitoring dynamic landscape change is a versatile way of facilitating rapid strategic decision making in a sustainable manner in a world of increasing complexity. Whilst a cadastral land information system is useful as a database, its use is limited for research purposes involving the manipulation of images - such as in studying flood-prone areas or land erosion susceptibility. In this paper, we report a land cover map for Mauritius Island (1859 km2), in the Indian Ocean, at a scale of 1:100,000 (A1-size paper). Inputs used to create the map are a SPOT satellite image, published map series at 1:25,000 scale, and selected ground truth surveys for validation. In total, 11 feature types, which are representative of the island's surface cover, have been mapped

Wetlands’ Inventory, Mapping and Land Cover Index Assessment on Mauritius.

Past studies conducted on wetlands of Mauritius lead to the conclusion that half of the wetlands have been backfilled for touristic and housing development and that the ecological condition of the remaining wetlands is being seriously challenged by numerous threats, natural and anthropogenic. This research aimed to fill the information gap concerning wetland type and distribution. For this, using published maps and satellite imagery, wetlands were digitised resulting in 144 wetlands and categorised into 8 ecological units. Afterwards, a number of wetlands were ranked according to their environmental condition based on a series of Land Cover Indices (LCIs). These indices were derived by analysis of land cover types and slope gradient within a 50 m and a 950 m watershed-bounded buffer zone. Wetlands in forested areas were the least disturbed, with LCI of typically 0.30, but potentially threatened by sediment accumulation due to a high slope gradient (>20 %). Three wetlands in Mauritius are classified as Ramsar wetland. One of them, the Blue Bay Marine Park (BBMP) has moderately good condition (LCI = 0.55). The other one, the Rivulet Terre Rouge Estuary Bird Sanctuary (RTREBS) was among the most heavily impacted (LCI = 0.87) due to intensive urbanization

Recommendations for riparian buffer widths based on field surveys of erosion processes on steep cultivated slopes.

Dans le présent projet, des relevés terrain ont été réalisés afin d’étudier les processus d’érosion sur des pentes cultivées proches des cours d’eau, et de proposer des mesures de conservation, particulièrement les largeurs des bandes riveraines. Les relevés terrain ont été faits dans un bassin versant de 108 km² dans la région de Portneuf, Québec, Canada. En utilisant un GPS (global positioning system) de poche, des rubans à mesurer, une image satellitaire à 0.5 m résolution et un modèle numérique de terrain (MNT) à 1 m résolution, 12 zones assujetties à l’érosion (totalisant 53 ha) et situées proches des cours d’eau ont été relevées pendant quatre journées durant la période de fortes pluies et de fonte de neige des mois d’avril–mai 2012. Le résultat est 328 traces d’érosion relevées et classées en 10 catégories. Les érosions prédominantes sont l’érosion en nappe et les ravinements au champ (70% de toute l’érosion observée). Les ravinements avaient des longueurs de 0.5–160 m, des profondeurs de 5–55 cm, et des largeurs de 5–130 cm. La plupart des traces d’érosions (n = 194) se produisent sur des pentes > 8% et ont des longueurs de 10–60 m. à l’heure actuelle, les bandes riveraines sur le terrain sont de 1–3 m, le minimum requis pour se conformer à la politique provinciale réglementant la largeur des bandes riveraines. Dans la plupart des zones relevées, le ravinement se fait tout simplement à travers la mince bande riveraine de 1–3 m pour aisément aller déposer les sédiments et polluants dans le cours d’eau. Sur la base des pentes évaluées, il est proposé dans cet article de convertir ces pentes cultivées en bandes riveraines de 10–60 m, de sorte que la bande de végétation agisse comme un tampon entre le cours d’eau et les cicatrices découlant du processus d’érosion en amont (en tant que sources de sédimentation et possiblement d’eutrophisation).Results of field surveys are used to build knowledge about erosion processes occurring on steep cultivated slopes next to watercourses, and to propose conservation measures with an emphasis on widths for riparian buffer strips. The surveys were conducted on a 108-km² watershed in Portneuf region, Québec, Canada. Using a handheld global positioning system (GPS), measuring tapes, a 0.5-m resolution satellite image and a 1-m resolution Digital Terrain Model (DTM), 12 erosion-prone areas, totalling 53 ha, located close to river banks were surveyed during four days of the rainy and snowmelt period of April–May 2012. As a result, 328 erosion features were identified and classified into 10 categories. Predominant erosion features included rills, ephemeral gullies and sheet erosion (70% of all features observed). Rills and smaller gullies had lengths of 0.5–160 m, depths of 5–55 cm, and breadths of 5–130 cm. Most erosion features (n = 194) occurred on hillslopes > 8% and had lengths of 10–60 m. At present, most riparian buffer strips in the surveyed field are 1–3 m wide, which is the minimum dimension required by the provincial policy that regulates vegetated filters. In most places surveyed, ephemeral gullying on steep slopes simply extends through the thin 1–3 m buffer strip to easily discharge sediments and pollutants into flowing streams. Based on the local slopes assessed, it is proposed herein to convert these steep cultivated hillslopes into riparian buffer strips of 10–60 m, so that vegetated strips effectively act as boundaries between watercourses and damaging uphill erosion processes, which are sources of sedimentation and, in all likelihood, eutrophication

Land cover of Mauritius Island

<p>In this digital era, high-resolution imagery offers a rapid and inexpensive means of monitoring land use changes. Digitally monitoring dynamic landscape change is a versatile way of facilitating rapid strategic decision making in a sustainable manner in a world of increasing complexity. Whilst a cadastral land information system is useful as a database, its use is limited for research purposes involving the manipulation of images – such as in studying flood-prone areas or land erosion susceptibility. In this paper, we report a land cover map for Mauritius Island (1859 km²), in the Indian Ocean, at a scale of 1:100,000 (A1-size paper). Inputs used to create the map are a SPOT satellite image, published map series at 1:25,000 scale, and selected ground truth surveys for validation. In total, 11 feature types, which are representative of the island's surface cover, have been mapped.</p

Quality assessment from a hydrological perspective of a digital elevation model derived from WorldView-2 remote sensing data

Nous avons évalué la qualité, d’un point de vue hydrologique, d’un modèle numérique de terrain (MNT) issu d’un couple d’images stéréoscopiques WorldView-2 (WV-2) en le comparant à des mesures de terrain obtenues par GPS. Deux méthodes d’évaluation ont été utilisées: (a) l’évaluation de la précision verticale et (b) l’évaluation hydrologique de variables de ruissellement. Trois parcelles agricoles de pentes différentes ont été choisies pour effectuer une évaluation de la précision verticale, suivie d’une évaluation comparative d’un ensemble de variables hydrologiques. Les résultats montrent une précision verticale globale de 0,45 m, ce qui confirme le potentiel des images stéréo WV-2 à extraire des informations altimétriques à haute résolution spatiale. En ce qui concerne les caractéristiques micro-topographiques à l’échelle de la parcelle, le modèle de terrain WV-2 obtient de meilleurs résultats sur les terrains aux pentes prononcées (5–10%), permettant l’extraction de variables telles que la longueur et la superficie totale de drainage des chenaux d’écoulement avec des erreurs relatives inférieures à 20%. L’extraction de caractéristiques telles que la pente, les exutoires des chenaux d’écoulement et les dépressions, a cependant montré qu’elle avait des limites dans les zones de faible pente (&#60;5%).A digital elevation model (DEM) derived from a stereo pair of WorldView-2 (WV-2) images was assessed against ground-truth GPS point datasets. Two assessment methods were used: (a) vertical accuracy assessment and (b) hydrological assessment of surface runoff variables. Three agricultural plots with different topographic slopes were selected to perform a vertical accuracy assessment, followed by a comparative assessment of a set of hydrological variables. The results show an overall vertical accuracy of 0.45 m, confirming the potential of WV-2 stereo images to extract elevation information at high spatial resolution. Concerning plot-scale micro-topographic features, the WV-2 DEM performed better on the plot with rolling slopes (5?10%), extracting variables such as the total length and drainage area of flow paths with relative errors lower than 20%. However, some limitations were detected in the extraction of variables such as terrain slope, drainage points of flow paths and terrain depressions in areas of flatter slopes (&#60;5%)