This work investigates wave energy attenuation by double trapezoidal porous structures of different structural parameters using a multi-domain boundary element method, under the assumption of small amplitude water wave theory. Two different cases are considered: (a) wave scattering by dual trapezoidal porous structures and (b) wave trapping by dual trapezoidal structures near a sloping porous wall, backed by a rigid wall. The reflection, transmission and dissipation coefficients along with the wave force exerted on the rigid wall are evaluated and analyzed to illustrate the effects of different structural configurations on wave flow. As a special case, wave scattering by a single structure is investigated and compared with the results for double trapezoidal structures. It is found that almost 90% of wave energy is dissipated by double structures, which is much higher than the energy attenuation in the presence of a single structure. For wave trapping, the results for four different cases are studied: (i) absence of any porous structures, (ii) presence of only a sloping porous seawall, (iii) presence of a single structure with the seawall and (iv) presence of double structures with the seawall. Wave reflection and force on the rigid wall are found to be significantly minimized by double structures as compared to that for the other cases. Finally, the findings of this study can give crucial information to the coastal engineers for designing varied combinations of trapezoidal porous structures as effective breakwaters.