HEFR as hydrology analysis tool
HEFR: Hydrology-Based Environmental Flow Regime
Strengths and Weaknesses
Strengths

Uses readily available data (i.e. gage records)

Relatively simple to calculate (nice tools)
Weaknesses

Lack of theoretical basis (linkage of a particular statistic to environmental health).

Has not been applied anywhere

Specificity - most matrix methods give a range for each criteria, HEFR is specific; reporting a single number
implies that only that number is protective of the environment. The precision of the numbers is not justified
by the method.

Sensitive to flow separation method and period of record. The values in the matrix will change depending
on the parameters used in the analysis and the period selected, even in cases where the historical flows
describe basically natural conditions.

There is very low confidence in the tables produced by the HEFR method alone describing a flow regime
adequate to support a sound ecological environment without considering other environmental factors
(biology, water quality and geomorphology).
Questions for BBEST
Pick a period
Pre-Impoundment
Post-Impoundment
Current Conditions
Period of Record
Pick a definition for wet, average and dry
Wet 75%
Average 50%
Dry 25%
Pick a statistical method (original or frequency‐based)
If frequency based, then define frequency
HEFR and the Flow Regime Components
Subsistence flows?
Base flows?
Pulse flows?
Flood flows?