Water planning glossary and units
These short explanations help with reading a plan. Definitions used by a particular assessment or dataset take precedence when interpreting its results.
Water and its movement
| Term | Reading definition |
|---|---|
| Withdrawal | Water taken from a source for use |
| Consumptive use | The part of a withdrawal removed from the immediate water environment, for example by evaporation or incorporation into products |
| Return flow | Used water returning to a water resource; check its destination and timing |
| Aquifer | Water-bearing geologic material capable of supplying usable quantities |
| Groundwater | Water below ground in saturated rock or sediment |
| Surface water | Water in rivers, lakes and other surface bodies |
| Basin or watershed | Land draining toward an identified outlet |
| Streamflow | Water passing a location over time |
| Effluent | Water leaving a treatment process |
| Dissolved oxygen | Oxygen present in water, relevant to aquatic conditions |
General hydrologic terminology can be checked in the USGS Water Science Glossary.
Planning and assessment terms
Baseline: the starting condition used for a comparison. Identify its date and whether it is measured, estimated or modeled.
Planning horizon: the future year a planning exercise looks toward. It is not a prediction that conditions remain fixed until that date.
Scenario: a set of assumptions used to examine possible conditions. Two scenarios can describe the same future year differently.
Planning node: a location used in a resource assessment. EPD's surface-water explanation describes assessments at selected basin locations. EPD assessment terminology.
Resource gap or challenge: a result indicating that a particular assessment criterion is not met under the conditions evaluated. Read the model, criterion, location and period; the label alone is not a complete description of an event.
Assimilative capacity: the receiving-water capacity considered in a water-quality assessment. Identify the pollutant, water-quality criterion and modeled conditions involved. EPD water-quality assessment.
Permitted capacity: a limit associated with an authorization. It should not automatically be treated as the amount actually used, the physical capacity of every component or the amount of water naturally available.
Management practice: an action or approach selected for the plan's objectives. Read its implementation requirements before describing it as a completed measure.
Benchmark: a stated way to assess progress. A benchmark describes how progress should be evaluated; an implementation record is needed to establish the result.
Units and comparison rules
| Label | Meaning | Common reading trap |
|---|---|---|
| MGD | Million U.S. gallons per day | Confusing a daily rate with a total annual volume |
| AAD | Average annual demand, where defined that way in the source | Treating an average as peak or dry-season demand |
| cfs | Cubic feet per second | Comparing it directly with MGD without converting units |
| mg/L | Milligrams per liter | Confusing concentration with total mass discharged |
| Percent | A share relative to a stated denominator | Comparing percentages with different denominators |
Always check the report's abbreviation list. Similar-looking labels can represent different quantities in different documents.
Three illustrative examples
Withdrawals and consumption: a fictional facility takes 10 units of water and returns 8 to the same system. The gross withdrawal is 10. The simplified difference is 2; whether that is the appropriate consumption figure depends on the accounting boundary, timing and definition. These are invented numbers, not Georgia data.
Average and peak: a system with an annual-average demand of 1 MGD can have days with higher demand. The average alone does not establish the capacity needed for a peak day.
Concentration and load: the same concentration discharged at different flow rates can represent different pollutant masses over time. A comparison needs both the concentration and the flow context.
Continue with how to read a regional plan or the source directory.