Time Allowance:
1.2.4. Flow Regime Components Definitions
Hydrology-Based Environmental Flow Regime (HEFR) Analyses for
Sabine-Neches Bay and Basin Expert Science Team (BBEST)
•
Subsistence flow – minimum streamflow needed during extreme drought conditions
•
Base flow – “normal” flow conditions found between storm events
•
High flow pulses – short-duration, high flows within the stream channel resulting from a storm
event
•
Overbank flows –high-flow events that cause flow beyond the riverbanks
TIFP Technical Overview
Overbank
the component of an instream flow regime that represents infrequent, high flow events that exceed the
normal channel. These flows maintain riparian areas and provide lateral connectivity between the river
channel and active floodplain. They may also provide life- cycle cues for various species.
High Flow Pulse
the component of an instream flow regime that represents short- duration, in-channel, high flow events
following storm events. These flows maintain riparian areas and provide lateral connectivity between the
river channel and active floodplain. They may also provide life- cycle cues for various species.
Base
the component of an instream flow regime that represents normal flow conditions (including variability)
between precipitation events. Base flows provide a range of suitable habitat conditions that support the
natural biological community of a specific river sub- basin.
Subsistence
the component of an instream flow regime that represents infrequent, naturally occurring low flow events
that occur for a seasonal period of time. They maintain sufficient water quality and provide sufficient habitat
to ensure organism populations capable of recolonizing the river system once normal, base flows return.
Time Allowance:
TSJ-BBEST Purpose Matrix
Taken from SAC Guidance: Use of Hydrologic Data in the Development of Instream Flow Recommendations for the
Environmental Flows Allocation Process and The Hydrology- Based Environmental Flow Regime (HEFR) (4/20/2009)
Overbank
Overbank flows are infrequent, high magnitude flow events that produce water levels that exceed channel
banks and result in water entering the floodplain. A primary objective is to maintain riparian areas associated
with riverine systems, eg, transport sediments and nutrients to riparian arease, recharge floodplain aquifers,
and provide suitable conditions for seedlings.
High Flow Pulse
High flow pulses are short duration, high magnitude (but still within channel) flow events that occur during or
immediately following rainfall events. They serve to maintain important physical habitat features and
connectivity along a stream channel.
Base
Base flows represent the range of "average" or "normal" flow conditions in the absence of significant
precipitation or runoff events. Base flows provide instream habitat conditions needed to maintain the diversity
of biological communities in streams and rivers.
Subsistence
Subsistence flows are low flows that occur during times of drought or under very dry conditions.
Time Allowance:
Ecological Roles
Taken from SAC Guidance: Use of Hydrologic Data in the Development of Instream Flow Recommendations for the
Environmental Flows Allocation Process and The Hydrology- Based Environmental Flow Regime (HEFR) (4/20/2009)
Overbank

Provide migration and spawning cues for fish

Provide lateral connection with oxbows, riparian habitats, and floodplain areas

Shape physical habitats

Drive lateral movement of the river channel

Provide nursery areas for juvenile fish

Recharge the floodplain water table

Deliver sediments and nutrients to the floodplain and estuaries

Create key habitat features such as snags

Maintain diversity in floodplain forest
High Flow Pulse

Provide migration and spawning cues for fish

Move fine sediments and expose cobbles and rocky substrate

Fill backwater areas and provide some lateral connectivity

Restore normal water quality conditions following prolonged dry periods.

Prevent riparian vegetation from growing in the channel

Scour macrophytes
Base

Provide habitat of sufficient depth and velocity, without excessive velocity which would require finding
shelter

Maintain water tables levels for riparian vegetation

Enable fish to move longitudinally to feeding and spawning areas

Keep fish and amphibian eggs wet and suspended

Provide drinking water for terrestrial animals
Subsistence

Sustain a minimum level of interconnection between pools

Provide sufficient flow to preclude lethal temperature and dissolved oxygen levels.

Purge invasive species