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We are interested in the sensor networks for scientific applications to cover and measure statistics on the sea surface. Due to flows and waves, the sensor nodes may gradually lose their positions; leaving the points of interest uncovered. Manual readjustment is costly and cannot be performed in time. We argue that a network of mobile sensor nodes which can perform self-adjustment is the best candidate to maintain the coverage of the surface area. In our application, we face a unique double mobility coverage problem. That is, there is an uncontrollable mobility, U-Mobility, by the flows which breaks the coverage of the sensor network. Moreover, there is also a controllable mobility, C-Mobility, by the mobile nodes which we can utilize to reinstall the coverage. Our objective is to build an energy efficient scheme for the sensor network coverage issue with this double mobility behavior. A key observation of our scheme is that the motion of the flow is not only a curse but should also be considered as a fortune. The sensor nodes can be pushed to some locations by the U-Mobility that potentially help to improve the overall coverage. With that taken into consideration, more efficient movement decision can be made. To this end, we present a dominating set maintenance scheme to maximally exploit the U-Mobility and balance the energy consumption among all the sensor nodes. We prove that the coverage is guaranteed in our scheme. We further propose a fully distributed protocol that addresses a set of practical issues. Through extensive simulation, we demonstrate that the network lifetime can be significantly extended, compared to a straightforward back-to-original reposition scheme.