Geography - rivers AS level

It helps to first think of a river with it's normal sediment supply. It has a fixed competence and capacity unless something happens to 'give' it more energy, however on the whole it has enough energy to carry it's load and deposits it at around about the same rate. If the river does gain more energy then its competence and capacity will increase and it will be able to carry more sediment or sediment of a larger size and its load may increase, but deposition will continue at the same rate because river energy has also increased. In the case of this question, energy hasn't increased, but the amount of sediment in the river has. This means that the river may not have the sufficient capacity to carry all of its new, increased load- as a result, deposition will increase because the river must deposit the sediment that it does not have the energy to carry. In other words, increased sediment supply means increase load. When load is increased, but the amount of energy the river has stays the same, then deposition will consequently also increase.
hope this helps