Wireless sensor networks (WSNs) are large collections of resource limited nodes, densely deployed over a landscape. They gather and disseminate local data using multihop broadcasting. WSN design and deployment is hampered by currently limited knowledge of the performance characteristics of network nodes and protocols. Their systematic development, thus, requires a flexible simulation environment in which new models of specific node or network behaviours can be integrated easily. This paper introduces a loosely coupled, object oriented simulation environment for this task. The simulator is used to investigate the efficiency of flooding protocols in WSNs. For dense networks with noisy transmission, we show that using low transmission power maximises time and resource efficiency and that the scalability of flooding for large networks is excellent. We demonstrate ways of improving flooding performance given specific deployment constraints.