A SEMI-AUTOMATIC APPROACH FOR DOLINE MAPPING IN BRAZILIAN COVERED KARST: THE WAY FORWARD TO VULNERABILITY ASSESSMENT

Abstract

Doline mapping is paramount in the vulnerability and risk as sessment of the underground karst environment by identifying cave-ground connectivity points at the surface. However, manual mapping is labour-intensive, slow and subjective, especially on a large scale. Therefore, the present study adopted a GIS-based semi-automatic approach for mapping large and medium-sized depressions/dolines in the Corrente river basin in Brazil, with a particular focus on the environmentally preserved areas of river Vermelho (APANRV Portuguese abbreviation) using remote sensing (DEM and Google Earth imagery) and field-based ob servations. Seven typical dolines forms (e.g., cockpit with drain insertion, collapse, collapse with river capture, suffosion, solu tion, cover collapse, and buried) are found from extensive field surveys. As an outcome of the proposed approach, two hundred and thirty-two medium to large-sized dolines have been identi fied and categorised into three main groups based on the cave density and local geology G1, G2, and G3. The high density of identified dolines (164 known caves) in G1 provides recon naissance for future speleological works in the preserved areas. Additionally, the presence of a considerable number of dolines in the adjoining areas (G2 and G3) stresses the need to revise the existing boundaries of the APANRV. Results correlate well with the dolines sites marked using field surveys and Google Earth images. This doline mapping may help researchers in the groundwater vulnerability assessment and the protection of spe leological heritage preserved in the caves.

Kartiranje vrtač je nadvse pomembno za oceno ranljivosti in tveganja podzemnega kraškega okolja, saj določa točke pove zanosti med jamami in tlemi na površju. Vendar je ročno kar tiranje zelo zahtevno, časovno zamudno in subjektivno, zlasti v velikih merilih. Zato je bil v tej študiji uporabljen polavtomatski pristop z uporabo orodij GIS za kartiranje velikih in srednje ve likih kraških globeli/vrtač v porečju reke Corrente v Braziliji s posebnim poudarkom na okoljsko ohranjenih območjih reke Vermelho (portugalsko APANRV) z uporabo daljinskega zazna vanja (posnetki DEM in programa Google Earth) in na podlagi terenskih opazovanj. Na podlagi obsežnih terenskih raziskav je ugotovljenih sedem značilnih oblik vrtač (npr. kokpit z drenažo, udornica, udornica z zajezitvijo reke, sufozija, škavnica, udornica, nastala z udorom/rušenjem jamskega stropa, in udornice, nastale z zasutjem). Kot rezultat predlaganega pristopa je bilo opredeljen ih 232 srednje velikih do velikih vrtač, ki so bile glede na gostoto vrtač in lokalno geologijo razvrščene v tri glavne skupine G1, G2 in G3. Velika gostota opredeljenih vrtač (164 znanih jam) v skupi ni G1 zagotavlja predhodni pregled za prihodnja speleološka dela na ohranjenih območjih. Poleg tega prisotnost velikega števila vrtač na sosednjih območjih (G2 in G3) poudarja potrebo po ponovnem pregledu zdajšnjih meja APANRV. Rezultati se dobro ujemajo z lokacijami vrtač, kartiranimi na podlagi terenskih ra ziskav in posnetkov programa Google Earth. To kartiranje vrtač lahko raziskovalcem pomaga pri oceni ranljivosti podzemne vode in pri zaščiti speleološke dediščine, ohranjene v jamah.