NWS Flood Thresholds Guide

Overview

The National Weather Service (NWS) maintains flood stage thresholds for thousands of stream gages across the United States. These thresholds define when water levels become hazardous.

Data Sources

Option 1: Bulk CSV Download (Recommended for Multiple Stations)

https://water.noaa.gov/resources/downloads/reports/nwps_all_gauges_report.csv

Option 2: Individual Station Pages

https://water.noaa.gov/gauges/<station_id>

Example: https://water.noaa.gov/gauges/04118105

Flood Stage Categories

Category	CSV Column	Description
Action Stage	action stage	Water level requiring monitoring, preparation may be needed
Flood Stage (Minor)	flood stage	Minimal property damage, some public threat. Use this to determine if flooding occurred.
Moderate Flood Stage	moderate flood stage	Structure inundation, evacuations may be needed
Major Flood Stage	major flood stage	Extensive damage, significant evacuations required

For general flood detection, use the flood stage column as the threshold.

Downloading Bulk CSV

import pandas as pd
import csv
import urllib.request
import io

nws_url = "https://water.noaa.gov/resources/downloads/reports/nwps_all_gauges_report.csv"

response = urllib.request.urlopen(nws_url)
content = response.read().decode('utf-8')
reader = csv.reader(io.StringIO(content))
headers = next(reader)
data = [row[:43] for row in reader]  # Truncate to 43 columns
nws_df = pd.DataFrame(data, columns=headers)