The duration of time that freshwater flows into estuaries differs with quantity of flows and the size of the river and estuary. Construction of roads increases the amount of impervious surface area. Surface runoff flows much more quickly over impervious surfaces than riparian surfaces. These surfaces also help humans intercept the water in storm drains before it reaches an estuary. The surface water that does reach a creek, stream or river does so at an accelerated pace. The freshwater inflows that estuaries do receive may come less frequent and at much larger volumes. The sudden change in salinity consequently negatively affects the estuarine flora and fauna.