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The objective of the OPAL (ref: PID2019-110311RB-C22) project is to identify and assess the major pathways delivering nutrients, trace metals and pollutants originated from anthropogenic activities to coastal Mediterranean lagoons connected to intensively used aquifers and their consequences on the lagoon geochemical cycles. One of its goals is “To assess of the role of storms and episodic events in the input of nutrients, metals and pollutants”. Within this framework, the capability of the hydrodynamic model Regional Ocean Model System (ROMS) to simulate fast increase of the Mar Menor coastal lagoon sea level due to extreme flood was tested. In September 2019 the stronger storm and flood registered in the Spanish Levantine area in 87 years occurred. In only 13 hours the sea level of the Mar Menor hypersaline lagoon of 135 Km2 increased 0.6 meters, thus creating a strong halocline due to the fresh water that entered from the floods. The sea level took near 7 days to restore. The morphology of the three outlets communicating the lagoon with the Mediterranean Sea determined their water flux going out the lagoon.This kind of extreme events produces significant enhancements of the inputs of nutrients, metals and pollutants to the lagoon water column coming from an intensive agriculture watershed. To understand the hydrodynamics behind this phenomenon, the ROMS model was used to simulate this episode. Simulations were validated against sea level, salinity and temperature recorded in the water and included surface water inflow from the land, wet/dry areas, bidirectional nesting, water exchange with the Mediterranean Sea and air/water interaction. The result obtained show the robustness of ROMS simulating this kind of events with two layer halocline system formed due to the fresh water inflow from land in a hypersaline water mass.

AUVs are self-propelled and able to navigate at an acceptable speed, but they need an electric motor and batteries that are limited in autonomy. Multivehicle fleet deployment can provide an adequate platform for conducting long term surveillance. Unexpected event detection can be more easily conducted if a set of vehicles in idle mode are expecting the occurrence of this event. Long term and high persistence are very interesting characteristics that a collaborative fleet of different vehicles can provide. However, the problem is the high cost of such kind of vehicles. The possibility of performing adequate tasks by using low cost underwater vehicle could multiply the number of agents in the area and therefore, providing high persistence and wide survey area capabilities. This paper progresses in the definition of the requirements needed to be applied on these kind of vehicles considering the low cost of construction and operation as one of the main goals. A more technological advanced and better equipped ASV as communication and coordination station in the area in combination with a fleet of robust Low Cost AUVs in collaborative schema seems to be an interesting platform for providing good results.

The challenge of extending the autonomy in AUV deployments is one of the most important issues in oceanographic research today. The possibility of maintaining a team of AUV under deployment in a defined area of interest for a long period could provide an additional source of information [8]. All this data in combination with the measures provided by buoys and sea gliders used for slow motion and long range operations will be very valuable. A group of low cost AUV's in alternative automatic switching system navigation-charging operation, could allow a kind of continuous surveying operation. This work is the continuation of the ideas that some of the authors previously presented in the AUV 2010 conference at MBARI [8]. At this conference was proposed the great interest for researching oceanic processes on two areas near Cartagena, Spain: cape Tiñoso and the Mar Menor a shallow coastal lagoon. Both areas require a different research structure configuration because of their opposite characteristics. The Mar Menor is a shallow salty lagoon 20 miles long with 7 m of maximum depth and particular features. This lagoon seems to present a sort of oceanic behavior and can be compared with the major oceans but a minor scale. The second area considered is cape Tiñoso, a very deep area in the Mediterranean Sea where the presence of a self-break provides an interesting potential for the research of the effect of upwelling currents., This work has been partly supported by the Spanish Ministry of Education under projects number TIN2011-28435-C03-01 and CTM2011-29691-C02-01.