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D6145-97 – Standard Test Method Technical Guide
Soil erosion and resulting sedimentation is the major cause of nonpoint source pollution that threatens water resources. ASTM D6145-97 (Reapproved 2018) provides a comprehensive guide for developing and implementing monitoring projects directed toward sediment in watersheds. It recognizes the need for a comprehensive understanding of naturally occurring and manmade impacts to the entire watershed hydrologic system.
⚠️ Major Nonpoint Source Pollutant: The standard identifies soil erosion and resulting sedimentation as the major cause of nonpoint source pollution. Impacts include impaired aquatic habitat, destruction of fisheries, lost reservoir capacity, increased flooding, and the transport of sorbed nutrients, pesticides, and heavy metals that can create toxic or eutrophic conditions.
📐 Scope and Key Sediment Parameters
This guide applies broadly to surface waters, including streams, rivers, lakes, ponds, reservoirs, estuaries, and wetlands (Scope 1.3). It is intended to provide general guidance and a series of general steps for establishing a monitoring program, rather than a strict implementation protocol (Scope 1.1 and 1.4).
The standard defines sedimentation as the detachment, entrainment, transportation, and deposition of eroded soil and rock particles. Specific parameters critical for a comprehensive monitoring program include suspended sediment, bedload, bed material, turbidity, particle size distribution, and sediment deposits.
| 🟦 Sediment Parameter | 📏 Description | 🎯 Environmental Relevance |
|---|---|---|
| Suspended Sediment | Particles transported in the water column | Water clarity, transport of sorbed pollutants |
| Bedload | Coarse particles moving along the stream bed | Channel morphology, aquatic habitat stability |
| Bed Material | Substrate composition of the stream bottom | Spawning habitat quality, benthic ecosystem health |
| Turbidity | Light scattering caused by suspended particles | Water clarity, light penetration, aesthetic quality |
| Deposited Sediment | Sediment in fields, floodplains, and channel bottoms | Floodplain aggradation, reservoir capacity loss |
⚙️ Strategic Framework and Monitoring Considerations
Following Guide D5851, this standard aligns with the Intergovernmental Task Force on Monitoring (ITFM) nationwide strategy. The goal is to improve the technical aspects of water monitoring to support sound water-quality decision-making and achieve a better return on investments in monitoring projects.
💡 Holistic Monitoring Approach: The standard advises that monitoring should include not only sediments suspended in water but also sediments deposited in fields, floodplains, and channel bottoms. A comprehensive understanding of the entire watershed hydrologic system is required to evaluate both natural and manmade impacts effectively.
The amount of sediment in a stream can affect channel shape, sinuosity, and the relative balance between riffles and pools. Excessive sediment decreases channel capacity, resulting in more frequent and larger out-of-bank floods. Indirect effects may include increased stream temperatures and decreased intergravel dissolved oxygen levels.
| ⚡ Strategic Phase | 📐 Key Focus Area | 📌 Guiding Principle from D6145 |
|---|---|---|
| Problem Identification | Erosion and sediment sources | Recognize natural vs. manmade impacts to the hydrologic system |
| Monitoring Design | Spatial and temporal coverage | Address both point and nonpoint source contributions |
| Parameter Selection | Physical and chemical metrics | Include suspended sediment, bedload, particle size, and chemistry |
| Data Evaluation | Trend analysis and impact assessment | Link sediment data to habitat quality, flooding, and channel morphology |
📊 Implications and Data Utilization
Well-designed monitoring projects detailed in this guide support effective water-quality decision-making by providing the data needed to evaluate erosion impacts, estimate sediment loads, and prioritize restoration efforts across the entire watershed. The guide emphasizes that the specific steps must be tailored to the unique physical and land-use characteristics of each watershed, recognizing that no single standard procedure applies to all situations.
❓ Frequently Asked Questions
© 2026 TNLab — This article is a technical interpretation for reference only. The original standard as published by ASTM International takes precedence.