Information Page: NileDeltaLobes
Grade level: High (9-12), Under graduate (13-16), Graduate / Professional
Statement: wave dominated delta changing wave field angles
Abstract: This is a coupled run of the HydroTrend River flux model and the Coastline Evolution model CEM. The run is not intended to simulate realistic conditions, but it is thought to be a proxy for the Nile delta. The simulation has two river draining to the coast; one has a wave field comming straight at it, the other wave field comes in under an angle. This results in different development; somewhat similar to the Rosetta and Damietta lobes of the Nile delta in Egypt.
For the Nile delta, the first run, kept all parameters constant as discussed above while changing only parameters found in the Wave and Avulsion component. The wave height was set to 1m, period of 6s, asymmetry of 0.4, and highness of 0.7. The avulsion component was set to have two rivers with no deviation, and was restricted to -60 and 70. This appeared somewhat similar to the real Nile with the major difference the angle of the rivers.
A delta is formed by the interaction of three main controls: river energy, wave energy or tidal energy. Deltas are often classified by their morphological characteristics and the dominant controlling factor cinfluencing its morphology. An open ocean basin has a potential for high wave energy. High wave interference causes conflicted or deflected river mouths. There is less influence from fluvial sources. In wave-dominated delta regions, breaking waves cause immediate mixing of fresh and salt water. Typically, the fresh water flow velocity decelerates rapidly. A bar may form in the immediate vicinity of the distributary mouth, often supplemented by landward migrating swash bars. The wave action reworks the sediment, making it much sandier than other types of deltas. Alternatively, sediment is delivered by the river and but it is immediately transported along the coast. The sediment is then deposited as beaches and bars and the development of distributaries is limited. Dominant directions of wave approach can result in asymmetric beach ridges, and may cause the progradation of a spit across the river mouth. This results in channel flow oblique or parallel to the shore.
For the theory behind the models of this coupled river and wave-dominated coast simulations see the Model Help of the Coastline Evolution Model: http://csdms.colorado.edu/wiki/Model_help:CEM and the Model help of HydroTrend: http://csdms.colorado.edu/wiki/Model_help:HydroTrend
This movie can be linked to the lab and lecture on coupled delta modeling: http://csdms.colorado.edu/wiki/SurfaceDynamics_Modeling_CMT http://csdms.colorado.edu/wiki/Labs_portal