The Lake Tahoe Basin Management Unit has used a variety of monitoring techniques to evaluate the success of stream channel rehabilitation projects. Water quality monitoring, channel cross-sectional profiles, aerial photogrammetry, and permanent photo points all provide useful information with varying costs and commitments.

Water Quality Monitoring

As a monitoring tool Water quality sampling can provide detailed and quantifiable information regarding the effectiveness of erosion control projects. Our strategy in water quality monitoring is to isolate the effects of the project by (1) sampling above and below and/or (2) sampling before and after the treatment, or (3) using a paired watershed approach. Sampling for water quality monitoring is scheduled to adequately describe the seasonal hydrologic fluctuations at a station. It is essential in water quality monitoring that data handling and analysis be defined prior to sample collection. This ensures that the data meets the needs of the analysis and project objectives. Water quality sampling provides a quantitative measure of the effectiveness of the erosion control project by measuring directly the item of concern, water quality. This type of monitoring is, however, labor intensive and can be quite expensive when equipment and analysis costs are added.

Channel Cross-Sectional Profiles

Channel Cross-sectional profile monitoring allows one to quantify the channel morphology of a system and evaluate its overall stability. This type of monitoring is carried out by profiling cross-sections spaced equally along the stream reach of concern. Interpretation of the scour and fill occurring over a long period of time allows one to determine trends in aggradation or degradation and thus recovery or decline along the stream reach. Channel cross-sectional profile monitoring is simple and inexpensive though it does require a long-term commitment. Furthermore, the quantitative data is only useful to assist a qualitative evaluation by the project manager thus requiring substantial on-site observations.

Aerial Photogrammet

Comparison of aerial photographs over time has been a popular planning tool for many years. New technology in the field of aerial photogrammetry has recently provided more options for the use of this technique in erosion control monitoring. In the case of the Lake Tahoe Basin Management Unit, a professional photogrammetry firm is contracted to make low elevation flights over a designated stream reach and produce a contour map, computer digitized map, selected cross sectional plots, and color transparent aerial photos. Aerial monitoring is an attractive monitoring technique as information on several aspects of the watershed is quickly gathered through one data collection technique. However, photogrammetry firms can be expensive and a commitment must be made to repeat this effort to quantify changes in the watershed over time.

Photo Point Monitoring

Photo point monitoring is an easy and useful means by which to document the recovery of an erosion control or restoration project. This monitoring technique involves taking photographs of the project from relatively permanent view stations prior to and for several years after project construction. The photos are then arranged in sequential order and assessed with respect to the vegetation growth and apparent site stability. Photo point monitoring requires only minimal cost and the data is easily collected and interpreted. Although photo point monitoring alone might not be sufficient monitoring, the results do provide an easy and attractive tool by which to help support program activity. In conclusion, long-term monitoring at Lake Tahoe in now an essential part of plans for managing the Basin. Only through monitoring can we know how well we're doing in improving and protecting Lake Tahoe's watershed through erosion control and restoration efforts.

Karen can be reached at (916) 573-2600