The process used to evaluate water quantity depends on whether you are examining rivers and streams, lakes, or groundwater. Each water system requires a different method of evaluation due to their physical characteristics.

The principal method for evaluating the quantity of water flowing in streams and rivers is by using streamflow hydrographs. A streamflow hydrograph is created using the data recorded from gauges installed in waterways. They tell us how much water is flowing past a point over time. The information is plotted on a chart and the result is a hydrograph.

To know how much water is in our lakes, we need to know two things.

1. The lake bottom, depth and shape.
   This is done using a method called Lake Bathymetry. Using sonar devices, the soundings are done to reveal the variations in depth. The lake bathymetry is then used to develop a relationship that describes how the surface area and volume change with depth. This relationship is useful for calculating water balances of lakes, since we can estimate the amount of water gained and lost as the lake level goes up or down. Completed bathymetric surveys are available for a large number of Alberta lakes. They may be ordered online from Map Town.

2. How levels in the lake change over time.
   This is done in a similar way to rivers and streams with the use of a recording gauge. The historical, or annual lake levels can be plotted on a chart as a hydrograph.

Groundwater resources are hard to quantify because of the difficulty in obtaining enough data to describe how the geology of the ground changes over a given area, and how the geology changes with depth below the earth's surface. You need to understand how different soil layers and aquifers interact with each other to quantify groundwater. This is often done using sophisticated computer flow modeling. A pump test can indicate the potential productivity and sustainable amount of water that can be extracted from a single groundwater well. However, to get an idea of the total volume of water stored underground available for that well, you need to know the extent and volume of the formation along with its geological properties. The geological properties of a formation can vary within the formation even if its extents are relatively well mapped. This means we can only estimate the potential of a groundwater resource for an area.

Precipitation is an important indicator of water quantity. Alberta Environment, in conjunction with other stakeholders, has a network of gauges throughout the province to measure precipitation. Because storms and rainfall can often be fairly site-specific (especially summer thunderstorms), the more stations you have to catch these events, the better. Our network of stations gives us a good idea of distribution and quantity of rainfall in Alberta. This information is critical to evaluate potential water availability. As part of its flood forecasting services, Alberta collects real time precipitation from a large number of stations across the province. Real-time precipitation summary maps are produced on a regular basis to give a general idea of the provincial precipitation distribution.