Several mathematical models have been developed in recent years to simulate hydrologic and sediment transport processed through vegetated buffer strips. Some of these models are empirically-based equations with limited applicability to conditions other than those under which they have been developed and the input data collected and used. There is a considerable amount of uncertainty in the application of existing process-based models as they consist of empirical sub-models in their structure. The inconsistency between the assumed section of erosion and deposition in and around the grass strip beds in the existing models is also a major limitation. Three independent predictive models are developed and presented in this thesis to fill in the gaps and to improve our predictive capabilities for hydrology and sediment transport across grass strips. The first model developed in this study is a process-based one capable of simulating surface water profile in the upstream section and within grass strips. The data from the experiments carried out earlier in Griffith University’s GUTSR facilities were used to develop a relationship between the hydraulic roughness and flow characteristics and to develop the model itself. The gradually varied flow equation was used to apply the new relationship and to calculate the flow characteristics in the upstream section and within the grass strip bed.