Prev Doc Prev Page Doc List USGS Home Contents Next Page Next Doc

Prev Doc | Prev Page | Doc List | USGS Home | Contents | Next Page | Next Doc

Thus, the size distribution of particles is determined and expressed in percentage by number of particles. A count of 100 particles is recommended; however, to determine percentages of particle sizes, 50 or 25 particles can be measured. To obtain a quantitative determination of finer grained bed material, three samples of the bed material are collected along each transect and composited. In addition, samples of the bank substrate material can be collected from one bank or both banks. These sa mples are returned to the laboratory for sieve analysis.

Permanent plot vegetation analysis is also suggested as a component of the second- level reach characterization. To construct a permanent vegetation plot, select an area at the end of each of the surveyed cross sections. A 20- by 20-m plot is identified by using a tape measure to determine the appropriate distance and a compass to establish 90-degree angles at the corners of the plot. The corners are then marked with semipermanent boundary markers. The edge of the plot nearest the bank edge should be at least several meters from the bank. Sample the vegetation by determining the diameter and species of all trees and shrubs within the plot. Record only living trees and shrubs. If the riparian zone is narrow such that a 20- by 20-m plot cannot be est ablished, then two or more smaller plots are established so that the total area sampled equals 400 m2. Where herbaceous vegetation is clearly dominant, then a 10- by 10-m square plot is established. At herbaceous vegetation plots, the aerial coverage of up to five species is measured, and the percent coverage of these species within the plot is calculated.

Mapping of all geomorphic channel units and habitat features can also provide critical information needed to evaluate temporal trends in habitat. Though the diagrammatic stream map should indicate the presence of these units and features to approximate scale, the first-level reach characterization does not attempt to quantify the occurrence of all features throughout the reach. In the second-level reach characterization, the two-dimensional area of all significant geomorphic channel units and habitat fe atures is determined.

Other instream and riparian features that can provide meaningful information on temporal changes in stream habitat should be considered as a part of the second-level reach characterization at all fixed sites. The procedures and techniques used in collect ing any additional habitat data must be documented to facilitate future data collection.

Synoptic sites

Synoptic sites usually number more than 15 per study unit and are not sampled continuously over time. Also, synoptic sites are generally designed to address various specific questions. Therefore, the approach used to collect habitat data at synoptic sites must be (1) flexible to accommodate the variety of questions being addressed at a synoptic site, (2) relatively rapid to facilitate data collection at a large number of sites, yet (3) capable of providing an adequate description of stream habitat at one point in time.

Habitat variables evaluated at synoptic sites are locally and regionally important. Therefore, the reach characterization conducted at synoptic sites should be locally designed with consideration of regional issues. The reach characterization conducted at synoptic sites, at a minimum, should consist of a subset of the first-level reach characterization conducted at fixed sites. Consistent data collection based on the techniques and procedures defined for the first-level reach characterization allows for data evaluation that includes