Monitoring the Red River delta environment

The Red River delta is the hub of all economic activity in the north of Vietnam, where the majority of the region's population is concentrated. The delta, which supports nearly half the country's rice production, is under threat due to its strategic position and unchecked population growth that is putting an increasing strain on resources. Food production is endangered by periodic flooding and environmental degradation caused by intensive farming methods designed to increase crop yields. Vietnamese planners are using satellite imagery to model and monitor change in an effort to solve the delta's problems.

Deforestation in the hills surrounding the Red River delta is leading to increased erosion, which in turn is causing more solid matter to be washed down to the delta. Alluvium that would otherwise provide rich nutrients for delta soils is blocked by levees built in the 18th century. And tectonic activity is causing basins barely four to five metres above sea level but as far as 60 kilometres inland to become permanently water-logged.

The rice harvest during the second half of the year is vital to food production in the delta. This period is invariably preceded by flooding that poses a serious threat not only to agriculture but also to the economy in general. One of the effects of new free-market policies has been to increase crop yields through intensive farming practices, which only degrade the environment further. Population densities exceed 1 000 inhabitants per square kilometre in the major cities of Hanoi and Haiphong in the north of the country.

 
Planting rice on the Red River delta.

A tool for monitoring change

A joint project involving the Cartel (Centre d'Applications et de Recherches en Télédétection) at Sherbrooke University in Quebec and the Institute of Geology (VTGEO) at Vietnam's Natural Sciences and Technology Centre has been set up to develop a tool for planners to monitor the delta's three main environmental hazards:

- increased soil erosion in the surrounding hills, leading to decreasing soil fertility, washing down of solid matter into the delta and silting up of reservoirs;

- repeated flooding at the heart of the delta around Hanoi, on the increase in recent years;

- unpredictable movement of the shoreline where the delta meets the sea, due to large quantities of alluvium deposited by the Red River and pronounced longshore drift.

GIS helps shape future policy

Satellite data acquired from several sources (Spot, Thematic Mapper, ERS-1) were loaded into a geographic information system (GIS) containing information on the environment of the Red River delta and surrounding regions. This GIS contains topographic data, maps and DEMs, digitized aerial photographs, geological and sociological data and a knowledge base providing information on the delta's dynamics. Radarsat data should also be included in the GIS in the near future.

Satellite imagery is used to monitor change and map landcover, stable features and areas susceptible to recurring hazards like monsoonal rains or exceptional ones like typhoons. Spot imagery was particularly useful in evaluating areas sown to the major crops in the Tien Hai district of Thai Binh province. Crop densities were then calculated in each district by overlaying crop classifications on existing maps. This information is very useful to planners who are trying to promote crop diversification.

Radiometric field surveys

Satellite data were supplemented and calibrated by in situ radiometric measurements to monitor crop densities. Cropping patterns and overlapping growth cycles in the delta throughout the year make it difficult to apply conventional image classification methods. Soil erosion was evaluated by mapping different erosion forecasting models then using these to estimate the rate at which dams on the Red River's tributaries are silting up, and by measuring vegetation cover on the surrounding hills to evaluate erosion risks. Green vegetation cover can be measured with sufficient accuracy using Spot imagery, but distinguishing between dry vegetation and barren land is more difficult. This task will be made easier in the future by the higher resolution provided by Spot 4's mid-IR instruments.

Training and resources

The project involved instructors, assistants and students from both partners and scientists in charge of environmental management in the delta's two provinces. Hardware and software required for processing satellite imagery and building a GIS was supplied by the local partners.

Training was provided by VTGEO researchers in Hanoi and on site in the provinces, which were able to define their needs exactly through close involvement in the project's early planning stages. Training used practical examples and real data from the provinces. The project was funded by the CRDI (Canada) and the AUPELF-UREF as part of its remote sensing network's joint research support programme. The delta has also been selected by ADRO as a survey site for validating the first images acquired by Radarsat.


Land use data for Tien Hal Thai Binh district, northern Vietnam according to classified Spot imagery (acquired on 25 August 1994).

Land use statistics for Tien Hal Thai Binh district, northern Vietnam according to classified Spot imagery (acquired on 25 August 1994).
Reference

Centre d'applications et de recherches en télédétection (CARTEL) - Sherbrooke University
F. Bonn, P. Lafrance, P. Cliche, I. Trépanier, J. Coulombe-Simoneau, Sherbrooke, Quebec, Canada, J1K 2R1
Tel: (+1 819 ) 821 7180 - Fax: (+1 819) 821 7944

VTGEO - Institute of Geology - Vietnam natural sciences and technology centre
Pham Van Cu, Nguyen Xuan Da, Nghia Do, Tu Liem, Hanoi -Vietnam
Tel: (+84 4) 35 14 93 - Fax: (+84 4) 25 00 00.