GISdevelopment.net ---> AARS ---> ACRS 1989 ---> Poster Session 1

Study and application of Remote Sensing techniques for groundwater investigation: Case-study of coastal
zones of Red River and Mekong River deltaic plains
of Vietnam

Nguyen Kim Minh Cong
Center of Geography and Natural Resources,
NCSR of Vietnam


Objectives and scope
The Coastal Zones chosen for the Studies are located in the Northern and Southern Vietnam respectively, that have a lot of differences not only on the geological, geomorphologic building-up also in the physico-geographical and meteoro-climatic characteristics.

Under the new socio-economic strategy of the Government of Vietnam, these areas are subjected to a period of intensified economic development and immense investment. Thus, the problem of detailed assessment of the Natural Conditions of the Areas has been raised and required a timely resolution. Consequently, the project RAS/86/141 named : "Application of Remote Sensing Techniques for the Study and Assessment of Natural Conditions, natural Resources and Development Dynamics of the coastal Zones of the Red River and the Mocking River Deltas" had been established and been sponsored and founded by ESCAP Organization.

Considering the potentials of Remote Sensing Techniques, the Directorate of the Project had entrusted the Staff of Geologists, Hydro geologists and Geomorphologies of the :Remote Sensing Application Division' of NCSR of Vietnam a subproject for Hydro geological Interpretations of the Lands at and Spot data for the aims of preparation of Hydro geological maps for the Study Areas.

The significant contributions of the Hydro geological Inter-pretations are supposed to be observed concerned mapping Regional geological features ane Tectonic domains that because of their colossal size and obscure ness under the soil-and vegetation-cover up-to-now stayed unmapped. The mapping of them will be very a significant input for study of the hydro-geological conditions and their re-assessment.

However, owing to the Scale of the Studies, and the inherent resolutions of the lands at and Spot imageries, the scope of the Hydro-geological Interpretations is expected to be limited, since only the Regional Structures, broad litho logic Groups and Macro-landforms, and thus, the main hydro geological nits can be identified.

Choice of materials and methodology
The basic data to be used for the Subproject "Hydro geological interpretations' has been the lands at MSS imageries (Black and White prints, available in a series from 1984to 19880 and the Spot FCC imageries, 9taken in February 1987) on the scale of 11/2500,000.

The following are considered as favorable environmental conditions for carrying out investigations ; 1) period of clean atmosphere and least vegetation cover : 20 Period of intensive development of groundwater natural phenomena and processes: 3) Period of calm sea surface. Hence, the mages taken during the dry season have been chosen for the interpretation work.

The data suitable for the investigations have been analyzed by visual interpretation techniques only. Due to the lack of possibility, the Advanced Computer Processing. Techniques such as supervised Classification, Bank-Rationing and Contrast Enhancement have not been conducted.

During the Interpretation Course, a significant supplementary information has been gained based on the Visual interpretations of the Lands at and Spot Films conducted on the Additive-Color Viewer (aC-90).

Annotation of various Strati graphic Units, Litho logic Groups and Hydro geologic Units has been taken from the Published and Archived Geological Literature and Maps complied by the "General Department of Geology and Mining of Vietnam".

Geological Information from the former conventional. On-ground investigations on Geology, Geomorphology and Groundwater has been generalized and evaluated and then used in term of the ground-truth information for checking the interpretation results.

Since the Areas were studied in details in the Geological Relations, the Ground Geological information has been collected and read by the Interpreters so that an adequate knowledge on Geology, Geomorphology and Groundwater has been provided to them prior to the Preliminary interpretation has been conducted independently, without special reference to the Ground information. only on the Final interpretation stage, the preliminary interpretation results have been revised wherever it was necessary according to the Ground information.

Interpretation works
Interpretation Procedure for the Aims of Hydro geological Studies of the Chosen Areas have been conducted on the four following sections :
  1. Litho logical Interpretation
  2. Structural Interpretations
  3. Geomorphologic interpretation
  4. Groundwater Interpretation
The realization of these specific geological studies is presented and discussed below :
  1. Lithological Interpretation
    The aim of Litho logical Interpretation has been identification and delineation of various litho logic units or various root types, based on such interpretation signatures as tone, texture, landforms, structural features, drainage and etc.

    As a rule, litho logical interpretation has a limited success, because the spectral reflectance characteristics of various rock types cannot be sufficient for their discrimination Nevertheless, supplementary interpretation signatures such as relief (mountainous relief, Karsts relief) enable the interpreters to identify correctly the Basaltic form actions (f , Q), Granite formations, limestone's sandstones, shale stones and some other rocks.

    For the loose quaternary sediments, for which the detailed Geological Mapping has been carried out, the application of Remote Sensing Techniques is very useful in revising the contacts and correlating the litho logic units. For example, for the first time, shoreline sand-dune formations have been identified and marked on the geologic Maps.

  2. Structural interpretation
    In comparison with the other geologic features, Interpretation of the Geologic Structures always gains much core successes.

    Thanks to the Synoptic overview from great altitude and Generalize of the Space Remote Sensing Data, the interpreters have been able to discern such geologic structures of great size and magnitude as faults fractures and circular structures.

    On the Study Areas, the deep faults of the foundation (basal faults) and the fractures of the Cenozoic Cover can be observed very clearly.

    A significant contribution of the Structural Interpretation has been founded in location and identification of he circular structures. The system of the interpreted laniary structures 9faults and fractures0 and circular structures, obviously, can create a remarkable evidence for the Neotectonic mobility and activities of the Study Areas.

  3. Geomorphologic Interpretation
    For the aims of Geomorphologic Interpretation, delineation of various landforms has been conducted on the basis of relief and form. The devoted landforms have been classified according to the landform-original principle. Similar Landforms have been group[ed into types based upon Geology and Prevalent Geomorphological processes. For the Study Areas, the following landform types have been found successfully :

    1. Landforms of Predominant Denudation Type
    2. Landforms of Mixed Denudation Accumulation Type
    3. Landform of Predominant Accumulation Type

    Beside this, morphologic elements such as shoreline (ancient and modern) : relics of dead rivers, relics of ancient tidal creeks and etc have also been identified and marked on the Geomorphologic Maps.

  4. Groundwater Interpretation
    The approach for Groundwater Interpretation has been delineation of various groundwater bearing units on the basis of Geology and Prevalent Hydro geological Processes.

    According to the nature of the water-bearing media, that can be extrapolated from the Geology, water-abundance degrees of various rocks or sedimentary deposits can be assumed and then revised by the Ground Geological Information.

    For the study areas, rocks and sedimentary deposits have been classified into several groups according to the water-abundance as follows :

    1. Rich and very rich in Groundwater aquifer of porous media (large pores)
    2. Moderate in groundwater aquifer of porous media (small pores).
    3. Scanty in Groundwater aquifer of porous-fissured or fissured media (small pores and Kars fissures)
    4. Aquiclude (Unleaking rocks) of rocky formations.

    Based on the Vegetation signature, on the knowledge of Groundwater Recharge-Transportation-Discharge and on the Prevalent hydro geological Processes (such as evaporation and encrustation) that are taking place under the hot protracted chemical types according to predominant anions compositions and total amount of dissolved solids (t.d.s), that have had the ground confirmation. These types are:

    1. Ultra-fresh groundwater
    2. Fresh Groundwater
    3. Saline Groundwater

    As a rule, Neotechtonic activities of Geologic faults and fractures always find their distinct expression in the Hydrogeology. This is because these activities more or less disturb the hydro geological situation and lead to appearance of some new phenomena (such as diffusion of different aquifers : discharge on the surface of low underlying aquifers (s) and etc)

    In the study area of the Mekong River delta, discharge on the surface of the low-lying thermal groundwater makes it possible to discern several thermal fountaining springs, that are distributed along the Basal faults of North-East trend.
Conclusions
  1. Space Remote Sensing data seems to be a very useful tool for Geological Studies, as it has been presented above.

  2. The gained interpretation results and the newly complied and Hydro geological maps can be a significant input for mineral prospecting (delineating target areas for ground water and oil-prospecting)…….