Hydrology is the calculation of the volume of water that will run off a defined catchment in a rain event. Hydraulics is the calculation of the flowrate, depth and velocity of the water that will run in channels and pipes.
Although, at first glance, this might seem more like pure civil engineering rather than environmental engineering, since protection of the environment is tied directly to risks and consequences, hydrology and hydraulics is absolutely essential in determining the risks and consequences when assessing water quality impacts. Hydrology tells us how frequent rain events are likely to be, in the catchment being assessed and how intense the event are likely to be, so that we can determine the risks. Hydraulics tells us how fast and what depth will be coming so we know what sized controls to use to slow it down. Hydrology and hydraulics also tells us the flowrate, which can be used to determine the pollutant load to a receiving water, which is essential in determining the consequences.
Erosion and Sedimentation Controls – The determination of the type and size of environmental controls is based on the environmental risk. The determination of the risk for erosion and sedimentation controls must be based on hydrology and hydraulics. On a small project that will only be exposed for a few months the size of the storm that is likely to hit the construction site is much smaller than for a 2 year project. That will change the size of the basins, channels and other controls that are required.
Expert Witness Land and Environment Court-1 – The EPA took an Agricultural producer to the Land and Environment Court after a million litres of untreated waterwater was spilled off site following an equipment failure. The EPA claimed that there would be significant damage to the receiving waters due to the incident. Eric Claus was able to show, using Hydrology and Hydraulics, that the risks of the pollutants in the wastewater getting to the receiving water were very low and that even if those pollutants did get to the receiving water, the pollutant load / consequences would not be dissimilar to events that happened regularly. The Judge accepted Eric Claus’ evidence and rejected the EPA’s claim that there would be significant impacts to the receiving waters.
Expert Witness Land and Environment Court-2 – The EPA took a Mining company to the Land and Environment Court following the spill of 3 million litres of high suspended solids water when a dam failed. The EPA claimed that there would be significant damage to the receiving waters due to the incident. Eric Claus was able to show, using Hydrology and Hydraulics, that the topography and ground surface of the path to the receiving waters was such that a significant percentage of the sediment would settle out prior to flowing into the receiving waters. This was verified with monitoring in the field. The Judge accepted Eric Claus’ evidence.