Washington NatureMapping - Water Module: Field Preparation

Water Module

Field Preparation

Physical Characteristics

Each stream has physical characteristics that are unique to that system. From the headwaters to the mouth, all streams are different. This is reflected in the fact that salmon stocks have developed to survive within specific stream systems. Stream width (measured in channel width and wetted width), stream gradient, and pool/riffle structure can all give an indication of the capacity and methods by which a stream can move water. It also becomes a indicator of the type of habitat that may be available within the system.

Large Woody Debris (LWD)

By looking at addition components of the stream, such as LWD, inorganic substrate (gravels in the bottom of the stream), and bank material and condition, it develops a biological picture of the watershed.
LWD (tress, limbs, root wads) within a stream or river can have a big influence on a stream. Not only does it provide an important input of organic material, it helps to create the dynamic structure of the stream.
Counting individual pieces of woody debris as well as the number of log jam gives an indication of available habitat to fish.

Pools and Riffles

A pool and riffle structure readily forms in a stream with sufficient LWD. This pool/riffle structure is critical to the development of adult salmon spawning areas and juvenile salmon rearing habitat. The type and amount of macroinvertebrates (stream bugs) are related to the pool/riffle structure of the stream. Some 'bugs' live in the riffles and others live in the pools. The diversity of the bugs is a reflection of water quality.

Organic Substrate

Organic substrates include things such as LWD and detritus (accumulated dead plant material). These material sources become an important food source for certain benthic macroinvertebrates (stream bugs). These in turn become an important food source for the other aquatic and terrestrial animals.

Inorganic Substrate

Inorganic substrates can be classified by their size. There are various ways to measure the gravels in a stream. Some methods require 'mechanical' (using different mesh) sizing of the various substrate types. Percentages of the different sized substrate gives an indication of the condition of the aquatic habitat. For a healthy salmon population, it is important to consider the amount of sand/silt and gravel that would be available for spawning and egg development.
Another way is to measure the streambed substrate is more subjective but allows for a quick analysis over larger portions of the stream. Determine the percentages of the following by scooping the streambed from three to four different places which characterize the streambed.

boulders > 12"

cobble/rubble 3-12"

gravel, and 1/4"-3"

sand/silt <1/4" commonly referred to as fines.

One way to visually check for the amount of silt in a stream is to work the heel of a boot into the substrate. Continue until just beyond the depth of your ankle. Remove your boot and observe the resulting plume of silt. If a plume silt comes out for a short time (10-20 seconds) and begins to taper off and then disappears from the source, then there is not a lot of silt.

When silt accumulation becomes too great, as is the case with excess surface runoff, it can be deposited in the gravel. Large silt loads in the streambed tend to bond or "cement" the gravel making it compacted. This becomes a concern for

adult fish trying to create redds for depositing eggs,

the fry which need the spaces between the gravel for oxygen, and

food for the fish (e.g., benthic macroinvertebrates).

Bank Material

Stream bank material may consist of clay, mud, dirt, rocks, stones or a mixture of all of above. This becomes important when characterizing the type and amount of sediment loading that may occur during various seasonal flows.

Bank Condition

The condition of a streambank gives an indication of the natural processes of the stream. Streams that are allowed to meander will show areas of erosion (along cut-banks) and areas of deposition (gravel bars). Streams are often controlled though by means of channelizing. By using some type of bank armorment such as rip rap, gabions, or concrete structures it can interfer with the natural process of bedload movement and flooding.
The vegetation along the riparian area is critical to the health of the stream. These structures can also be used reinforce bridges and culverts.

Channel Configuration

This gives an indication of the capacity for the stream to move water. Stream channels can be measured from bank-to-bank (bank-full width) and from each edge of the stream (wetted width).

Bank-full width is the width of the steam at normal high water events. This is primarily determined by considering differences in vegetation (aquatic vs typical terrestrial) and physcial characteristics of the stream bank. Wetted width is the actual width of the stream from water edge to water edge.

Restoration projects may strengthen the bank by adding:

gabion - a structure usually rocks enclosed in a chain link fencing material to act like a retaining wall to reinforce a bank or divert water.

rip rap - rock material (large rocks/boulders) that is most often placed along a stream bank to reinforce the stability of the bank.

crib wall is usually a wooden structure to retain material along the bank. semi-arid

wiers

natural materials (bundles of stems, root systems, large woody debris, etc.) to stabilize the site. This is a form of bioengineering.

Weirs are put in streams to regulate the flow of water in a stairstep fashion. They are used when tryng to decrease the gradient of the stream. The picture shows the a low-flow notch in the log weir. This particular stream has little or no flow during the summertime. There are large wetland systems above this replaced culvert project which is critical over-summer rearing habitat for juvenile Coho salmon.

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