Natural vs. Modified HabitatPrimary Headwater Habitat Streams
Headwater Habitat Evaluation Index
What qualifies as a Natural PHWH stream?
Characteristics:Characteristics: A Watercourse with:A Watercourse with:
A defined BED and BANKA defined BED and BANK Either continuous or periodic FLOWING waterEither continuous or periodic FLOWING water A drainage generally LESS than one square A drainage generally LESS than one square
mile mile Deepest pools < 40cmDeepest pools < 40cm Widely divergent communities based upon in Widely divergent communities based upon in
stream Biologystream Biology No No ChannelizationChannelization1
What do Natural PHWH streams do?
Major Downstream Exports:
1. Desirable Biomass1 (fish, plants, birds, mammals, sensitive species)
1. Low Sediment2 Delivery
2. Water Quality Suitable for ALL Uses
Un-impacted PHWH Stream
What qualifies as a Modified PHWH stream?
Characteristics: A Watercourse with:A Watercourse with:
A channelized or moved course Man-made ditches Silt infilling Erosion1
No flowing water A filled or buried bed Increased sunlight from vegetation
removal Chemical pollution
What do Modified PHWH streams do?
Major Downstream Exports
Nutrients & Undesirable Biomass (algae, detritivores1, tolerant2 species)
High Sediment Delivery
Degraded3 PHWH Stream
A Natural Primary Headwater Stream
PHWH (Class III)
A Modified Primary Headwater Stream
PHWH (Class I modified)
Natural over Modified PHWH(Upland Benefits)
Increases land value
Reduces erosion Reduces or prevent
flooding Increases wildlife
habitat Increases beauty
Natural over Modified PHWH(Downstream Benefits)
Reduces flooding & channel scour1 (energy)
Processes nutrients & sediment Protects downstream ecology & water
quality Protects drinking waters supplies
Consequences of Continued Degradation of PHWH Streams
-Increased degradation of larger streams
-Increased maintenance costs
-Decreased wildlife habitat
-Other consequences
Glossary
Biomass - the total living biological material in a given area or of a biological community or group - biomass is measured by weight, or by dry weight per given area (usually measured per square meter or square kilometer)Channelization - the process of reconstructing the natural course of a stream in order to make it flow into a restricted pathDegradation - The wearing down of the land by the erosive action of water, wind, or iceDetritivores - Animals that consume decomposing organic materials and in doing so contribute to decomposition and the recycling of nutrientsDry Weight - the weight of the material minus the weight of water in the material - dry weight is often calculated by drying material until it no longer loses weight due to evaporationEncroached - To advance beyond proper or former limits
Glossary - continued
Entrenched - Established firmly and securelyEroding - displacement of solids (soil, mud, rock and other particles) by the agents of ocean currents, wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion)Scour - Debris flows and floods may also occur when strong rains on hill or mountain slopes cause extensive erosion and/or what is known as "channel scour"Sediments - the matter that settles to the bottom of a liquid - in streams the sediments are the suspended particles that settle out when flow stopsTolerant Species - species that are able to tolerate environmental conditions or physiological stress, showing the capacity for endurance