Identification of the changes in Manning's coefficient for Erbil Basin using the ArcGIS, HEC-RAS and remote sensing images.

The Manning coefficient (n) is considered one of the important and influential hydrological parameters in hydraulic models, which gives a clear indication of the nature of the land cover (roughness) and the extent of the land's surface resistance to water flow. Therefore, the study focused on estimating the values of n and the extent of changes occurring in it during the study period from 2017 to 2023 in Erbil governorate, Iraq. This has a clear impact on building and simulating future hydraulic models and reducing flood risks in the study area. The study relied on the use of integrated techniques for ArcGIS, HEC-RAS, and remote sensing (RS) imagery, to understand the locations of changes in the n as well as its magnitudes due to continuous changes in the nature of land use. Erbil governorate is witnessing major changes due to rapid urban development and this has a clear impact on the nature of water flow on its surface. The Sentinel-2 satellite provided useful and important images and data for analyzing land cover patterns in the study area. ArcGIS technology has given an important opportunity to classify regions in terms of the percentage of urban areas, forests, and grasslands as well as water bodies. While the HEC-RAS program contributed to determining the n values corresponding to the codes extracted from ArcGIS and the related standard values approved in the TF55 file. The study showed clear changes in the n value, ranging from 0.02 to 0.11 in the study area. This reflects the percentage of losses in lands covered with vegetable grass and the increase in urban areas, and thus the clear impact on the dynamics of water flow and the increase in flood risks. This study can provide important indicators for decision-makers, planning agencies, and those concerned with the environment in Iraq and Erbil governorate in particular on how to deal with the challenges of land use patterns and their impacts. The study emphasizes the need for a balance between economic and social development, preserving the environment, and enhancing its sustainability safely. [ABSTRACT FROM AUTHOR]