---
title: Delineating Your Watershed for Assessment
description: "## Summary When conducting a watershed assessment, the first practical step is to delineate the watershed boundary on a topographic map. This page walks through the process of using contour lines to identify ridgelines and trace drainage boundaries. For general…"
url: "https://aml-connect.org/aml-knowledge-base/delineating-your-watershed-for-assessment/"
updated: "2026-03-13"
category: Watershed Tools and Methods / Assessing the Watershed / Conducting the Assessment
---

# Delineating Your Watershed for Assessment

## Summary

When conducting a watershed assessment, the first practical step is to delineate the watershed boundary on a topographic map. This page walks through the process of using contour lines to identify ridgelines and trace drainage boundaries. For general background on what a watershed is, see Mapping Your Watershed in the Watershed 101 section.

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To begin mapping your watershed, first collect all of the materials you will need.  A pencil and a topographical map are very helpful.  Topographical maps display physical features of the land such as hills, valleys, ridges and channels.  A map can be obtained through your local USGS (US Geological Survey), a map store, or from your local conservancy.  The lines on a "topo" map represent the altitude of that area.  Closely spaced lines indicate rapid changes or steep slopes while widely spaced lines represent gradual changes.

1) Use a topographic map to locate the river, lake, stream, wetland, or other waterbodies of interest.

![](https://i0.wp.com/amrclearinghouse.org/Sub/WATERSHEDbasics/step1.jpg)

2) Trace the watercourse from its source to its mouth, including the tributaries.  This step determines the general beginning and ending boundaries.

![](https://i0.wp.com/amrclearinghouse.org/Sub/WATERSHEDbasics/step2.jpg)

3) The lines on the map are known as contour lines.  Contour lines connect all points of equal elevation above or below a known reference elevation.  The numbers beside the lines indicate  the elevation.  Thin lines mark 10 foot intervals in elevation, while thick lines mark 50 foot intervals in elevatioon.

![](https://i0.wp.com/amrclearinghouse.org/Sub/WATERSHEDbasics/step3a.jpg)

Contour lines that are spaced far apart indicate that the land is gently sloped and more level.  Closely spaced lines, however, indicate steep changes in elevation over a short distance.

![](https://i0.wp.com/amrclearinghouse.org/Sub/WATERSHEDbasics/step3b.jpg)

For the following steps go [here.](http://amrclearinghouse.org/Sub/WATERSHEDbasics/ZZMappingSteps.htm)

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## Related Pages

- [Mapping Your Watershed](/docs/mapping-your-watershed) (Watershed 101) -- General introduction
- [Establish Sampling Points](/docs/establish-sampling-points) -- Next step after delineation
- [Report AMD Discharges](/docs/report-amd-discharges) -- Documenting what you find
- [Background Search](/docs/background-search) -- Gathering existing information first

## Source and Last Reviewed

Source: AMR Clearinghouse (amrclearinghouse.org). Migrated to AML-Connect. Last Reviewed: 2026-03-13.

**Tags:** assessment, monitoring, planning, practitioner