22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

DISTRIBUTARY FLOW IN KARST SYSTEMS: GEOLOGICAL AND CLIMATIC CONTROLS

26 Sep 2019, 15:30
15m
Multiuse room 2 ()

Multiuse room 2

Oral Topic 7 - Karst Hydrogeology Parallel

Speaker

Dr Augusto Auler (Instituto do Carste)

Description

Divergent or distributary flow routes are frequent in karst systems, as demonstrated by numerous tracing experiments throughout the world. However, distributary flow is less common in surface systems, in which streamflow favours the convergence towards the base level. Distributary flow systems are also in contrast with the initiation and development of conduits in carbonate rocks, where flow in faster developing passages distorts the equipotential field, causing the abandonment of some routes or the convergence of channels, resulting in dendritic cave systems, the most common cave pattern. It appears thus, that distributary groundwater flow is not to be expected in natural systems, and its recurrence in karst systems requires an explanation.

Dissolutionally enlarged joints and bedding planes are the most common avenues of flow in karst systems, but as matrix permeability tends to be very low, especially in mature carbonates, flow in high permeability channels will behave as “confined” flow, in which small variations in head can result in the exploitation of alternative routes, commonly represented by nearby bedding planes or joints. This situation is favoured in carbonates in which the vertical distance between these alternative horizons is within the range of natural vertical variations in elevation of the phreatic zone. Low dipping, well-bedded carbonates, especially in situations when the dip coincides with the direction of the hydraulic gradient are especially prone to the activation of alternative routes.

The interplay between water table rise, variations in base level (thus favouring changes in the elevation of discharge zone), seasonal/episodic recharge and horizontally bedded carbonates can foster the creation of distributary routes, mostly under episodic situations, related to specific climatic conditions. Tracing under distinct recharge situations may thus be crucial in delineating the true character of groundwater flow routes in karst terrains, although in seasonal climates or under flooding scenarios, such as in many tropical areas, this implies in difficulties for access and proper monitoring.

Primary author

Dr Augusto Auler (Instituto do Carste)

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