Wireless Sensor Networks (WSNs) are based on elementary sensors that detect the occurrence of particular events in a monitored area. Among the recent critical WSN applications one can find the border surveillance applications. The first aim of this class of applications is to monitor a country border and detect the presence of intruders near the border line. In this paper, we investigate theoretically the effects of natural factors on dynamic deployment scheme of a hierarchical WSN-based solution providing two lines of surveillance. Parameters such as the wind effect, the altitude and velocity of the airplane from which the sensors are thrown are put into equation to optimize the area coverage and WSN connectivity. Then, we propose mathematical models that evaluate the quality of connectivity and coverage of the deployed network and allow planning and dimensioning of a border solution.