Numerical Simulation of Flood Inundation around Aq Qala Industrial state and Remedies for its Protection

Aq Qala industrial state is one of the most important infrastructure in Golestan province. The layout of this area in the vicinity of Gorganrood and Gharesoo rivers connected by Shurhayat channel has increased its vulnerability against medium and large floods. March 2018 flood in Golestan province has just revealed many weak points of this area versus any upcoming floods. Therefore, in this paper the author tries to deal with the problem in order to remedy Aq Qala industrial state resilience against future possible flood. In addition, it is attempted to find a reliable solution to protect this area. Various numerical models have been developed for simulation of flood inundation to delineate the floodplain zones bordering the rivers and calculate the associated risk considering various return periods. Numerical models to simulate floods are categorized into (a) one-dimensional (1D) models, (b) two dimensional (2D) models, and (c) one-dimensional river flow models coupled with two-dimensional floodplain flow (1D-2D) models. In this paper, due to two-dimensional behavior of flood flow around the state MIKE-HD model widly used by many resarcher is used to simulate flood around the region. To achieve this, initially the MIKE-HD model was calibrated and validated for the rivers an flood pain at the studty area and subsequently, the flood inundation is simulated using MIKE-HD for various return periods. The simulated flood inundation is validated using March 2018 flood. This flood was one of the biggest flood in previous 500-year by which many houses were evacuated for 3 weeks intensifiing by snowmelt for another 2 weeks. Several cities and villages in Golestan Province in Iran were engaged by this flood in more than 200 km area at Gorganrood river neighborhood.

In order to simulate flood inundation around the industrial state many factors and parameters must be considered. The first requirement is topographical data which are important to clear the flood flow direction. In this study, three datasets are used while the first one goes back to data gathered by photogrammetric operation. In this data set more than 6799 hectares are surveyed by drone with an accuracy abour 20m to 50m. The second one goes back to the ground survey around the industrial state while the last one is related to the Gorganrod bathymetrical data provided by Golestan province Regional Water Organization. After gathering topographical data sets together an event is considered to calibrate flood model in the MIKE-HD software with two parameters including water levels and flood inundation area. To achieve this, the flood occurred in March 2018 is chosen as the event. In this flood many parameters such as the observed flood plain by aerial images and water levels are considered as calibration parameters. In the model the bridge laid on Aq Qala-Gogran road over Gharehsoo river was taken in to th accout to make the more accurate. Finally, the model is developed and evaluated versus various flood with different return periods. Results show that the maximum water level for 500-year return period is -15.94m CD. Also results show that the behavior of flood flow in the area has a two dimensional behavior with low speed. This show that protection alternatives like river dikes haven’t got any problem to be collapsed by scouring. Also, it is concluded that the obtained water levels for diferent return periods converge to each other in the highest value of return periods.

Obtained results show that the flood flow has a two dimensional behavior in the study area for all return periods so floods showing themselves by water level changing and inundation. This confirms two options for the industrial state protection against future possible flood. The first one is construction of walls to protect the area while increasing the levels of foundation for the structures can be the second alternative. However, changing level of foundation for the client is too difficult because most of the buildings are constructed now and any movement or changing in this way is not cost-effective. In addition, to protect the industrial area from runoff inundation construction some pump stations can be recommended specially for flood times. The pump station are remedies to convey produced runoff by the area at rainig time on the back of protection wall especially in inundation time. Also results show that a level about -15.94 CD can be a fair level to construct the protection wall as the ulimate level. Not that wave and wind-setup freebords must be added to this level because of inundation enduring.

In this study flood flow around Aq Qala industrial state was studied. Result show that the best option for protection of the study area is flood wall along with 9 pump stations at the lower level areas. Highlights about the study can be categorized as follows:1- Simulation of March 2018 flood at the study area 2- Finding final options for the protection of the industrial state against future possible flood3- Flood levels for various return periods and its ultimate values4- Flood behavior for the flat area like Aq Qala industrial state is showing itself as level fluctuation rather than a high velocity fluid flow5- In order to remedy flood inundation at the study area considring wave and wind setup as a free board to design the protection wall is essential.Keywords: Inundation, Aq Qala Industrial State, MIKE-HD, Protection, Flood