Development of a framework for sand auditing of the Chaliyar River basin, Kerala, India using HEC-HMS and HEC-RAS model coupling

ABSTRACT

Excessive sand mining to meet the growing demands of the construction industry has resulted in the degradation of rivers, lowering of groundwater table, saltwater intrusion into coastal aquifers, and damages to the biodiversity of the riverine ecosystem, besides endangering bridges and hydraulic structures at several locations. Methods presently being employed to assess the amount of sand that can be mined from rivers lack a scientific basis and are seldom supported by systematic studies on the behaviour of riverine systems. Sand audit reports shall be prepared based on hydrologic, hydraulic, and sediment transport modelling of rivers, and shall take into account relevant environmental and ecological considerations. These reports shall clearly present details pertaining to the annual sediment yield of the river basin, reaches of the river/ locations from which sand can be extracted without disturbing the river sediment equilibrium, and the volume of sediment that can be extracted from these locations. Sand mining from rivers is a major environmental issue in Kerala and the urgent need for regulating sand extraction based on a scientific assessment of the amount of sand available is widely recognized. It is in this context that this work aimed at developing a framework to perform sand auditing was taken up. The methodology is demonstrated by applying it to the Chaliyar River in Kerala. Rainfall-runoff and soil erosion modelling, and sediment routing were performed in HEC-HMS. Soil erosion from the catchment was modelled using the Modified Universal Soil Loss Equation (MUSLE) and the sediment was routed through the river by the uniform equilibrium method. Hydraulic and sediment transport modelling was then performed in HEC-RAS. Values of the model performance criteria for both HEC-RAS and HEC-HMS indicate that these models performed reasonably well. Based on the analysis, a sand audit report and sand volume map were prepared.

KEYWORDS:

• Sand mining
• sand audit report
• sediment modelling
• HEC-RAS
• HEC-HMS
• Chaliyar River

Disclosure statement

No potential conflict of interest was reported by the author(s).