Usage of Particle Filter for Exact Estimation of Constant Head Boundaries in Unconfined Aquifer

Having the exact values of boundary conditions is one of the effective way to accurate groundwater models. In the present study, the exact value of constant head boundaries in Birjand aquifer is specified with the usage of particle filter linked to meshless groundwater model. Particle filter known as one of the data assimilation methods applies to dynamic systems in order to improve their performance. Meshless model, one of the numerical models that do not mesh the problem domain, enforces the governed equation to nodes. Birjand aquifer with almost 269 km2 area, has 190 extraction and 10 observation wells. There are also nine inflow and one outflow regions with constant head boundary conditions, which include 105 boundary nodes. After determination of the lower and upper bounds of groundwater head for each node, the exact values of this parameter is computed. Finally, the simulated groundwater head compared with observation data. The closeness of the achieved results to the observation data showed the performance of the engaged method, as the results indicated a significant decrease in RMSE occurs just with the usage of particle filter linked to meshless model. RMSE value reduced to 0.386 m as its previous value was 0.757 m. The results also showed that the model was more accurate when the number of particles in particle filter increased. The RMSE value for 500, 700 and 1000 particles were 0.484, 0.401 and 0.386m respectively.