Design of Forest Riparian Buffer Strips

for the

Protection of Water Quality:

Analysis of Scientific Literature

Idaho Forest, Wildlife and Range Policy Analysis Group

Report No. 8

by

George H. Belt,1

Jay O'Laughlin,2 and

Troy Merrill3

June 1992

_______________________________

1Professor of Forest Resources, College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, ID 83843.

2Director, Idaho Forest, Wildlife and Range Policy Analysis Group, University of Idaho, Moscow, ID 83843.

3Research Assistant, Idaho Forest, Wildlife and Range Policy Analysis Group, University of Idaho, Moscow, ID 83843.

ACKNOWLEDGEMENTS

The efforts of the Technical Advisory Committee, listed below, are gratefully acknowledged. These individuals provided guidance on the design of the plan for this study, and provided technical review of the final draft of the report.

Dr. C. Michael Falter
Professor of Fisheries, and Head
Department of Fish & Wildlife Resources
University of Idaho		 Lyn Morelan
Boise National Forest
Boise, Idaho
(Chair, Idaho Forest Practices Act Advisory Committee)
Dr. Robert L. Mahler
Professor, Department of Soil Science
University of Idaho		 Dale McGreer
Potlatch Corporation
Lewiston, Idaho
(Member, Idaho Forest Practices Act Advisory Committee)
Dr. Roy Mink
Professor of Geology, and Director
Idaho Water Resources Research Institute
University of Idaho		 John T. Heimer
Fishery Staff Biologist
Idaho Department of Fish and Game
Boise, Idaho

One other individual provided technical review of the final draft of the report:

Dr. Kenneth J. Raedeke
Research Associate Professor of Wildlife Biology
College of Forest Resources
University of Washington

TABLE OF CONTENTS

Acknowledgements i
List of Tables & Figure iii
Foreword iv
Executive Summary 1
Focus Question Summary Replies 2
Introduction 6
What is a Buffer Strip? 6
  • Buffer Strip Requirements in Idaho, Washington, California, and Oregon
7
    • Idaho: Stream Protection Zones (SPZs)
7
    • Washington: Riparian Management Zones (RMZs)
9
    • California: Watercourse and Lake Protection Zones (WLPZs)
9
    • Oregon: Riparian Management Areas (RMAs)
10
  • Comparison of Buffer Strip Requirements in Four States
10
How do Forest Practices within Buffer Strips Affect Water Quality and Fish Habitat? 11
  • Effects of Canopy Removal
11
    • Stream temperature
11
    • Cover, primary production, and salmonid habitat
13
  • Effects of Timber Harvesting
13
    • Large organic debris (LOD)
13
    • Sediment production and soil compaction
14
  • Effects of Slash Burning on Water Quality
14
How Effective are Buffer Strips in Reducing Impacts of Forest Practices? 14
  • Effectiveness Trapping Sediment or Nutrients
15
    • Trapping or filtering sediment from logging roads
15
    • Filtering nutrients and sediment from forest lands
17
    • Trapping nutrients and sediment from agricultural lands
18
  • Effectiveness Moderating Stream Temperatures
18
    • Stream temperature elevation and control following harvesting
18
    • Shade from riparian vegetation and stream temperature
19
    • Buffer strip width and stream temperature
19
  • Effectiveness Providing Large Organic Debris (LOD)
19
  • Effectiveness Controlling Cumulative Effects
20
  • Effectiveness Providing Food and Cover
20
  • Cost Effectiveness of Buffer Strips
21
What are the Issues in Buffer Strip Design? 22
  • Fixed Minimum vs. Variable Widths
22
  • Removal of Vegetation
23
  • Multiple Design Criteria
23
What Models are Available for Use in Buffer Strip Design? 24
  • Water temperature Models
24
    • TFW Water Temperature Screening Model
25
    • TEMPEST Model
25
    • TEMP-86 Model
25
  • Surface Runoff-Based Variable Width Buffer Model
25
  • Sediment-Based Road, Buffer Strip Model
26
  • LOD Recruitment Model Based on Conditional Probability
26
Literature Cited 27
Glossary 32

LIST OF TABLES

Table 1. Minimum number of standing trees to be left within 50 feet of each side of all Class I streams in Idaho, per 1,000 feet of stream. 8
Table 2. Stream buffer strip requirements in four states. 12

FIGURE

Cover. Shaded areas indicate the 41 percent of the State of Idaho that is covered by forests (adapted from Benson et al. 1987).

FOREWORD

The Idaho Forest, Wildlife and Range Policy Analysis Group (PAG) was created by the Idaho legislature in 1989 to provide Idaho decision makers with timely and objective data and analyses of pertinent natural resource issues. A standing nine-member advisory committee (see inside cover) suggests issues and priorities for the PAG. Results of each analysis are reviewed by a technical advisory committee selected separately for each inquiry (see the acknowledgements on page i). Findings are made available in a policy analysis publication series. This is the eighth report in the series.

This report analyzes the design of stream protection zones (SPZs), a particular best management practice to protect water quality on timbered stream reaches in Idaho. The request for this analysis came from the Director of the Idaho Department of Lands (IDL), the agency responsible for implementing the Idaho Forest Practices Act. Developing consensus on the design of SPZs to protect water quality from the impacts of forest practices on some of Idaho's stream segments of concern has proven to be difficult. To facilitate the consensus-building process, the IDL Director requested that the PAG evaluate scientific information "regarding relationships between forest practices SPZs, water quality, and fishery habitats."

What does scientific research say about the effectiveness of streamside buffer zones in protecting water quality? The summary of research-based knowledge in this report answers that question. We hope this information will be useful in helping resolve the issue of how to design Idaho's stream protection zones.

John C. Hendee, Dean
College of Forestry, Wildlife and Range Sciences
University of Idaho

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