U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-052-02

May 2002

WaterWatch —Maps and graphs of current water resources conditions

Map of real-time streamflow compared to

historical streamflow for the day of the year (United States)

Introduction

WaterWatch is the official

U.S. Geological Survey (USGS) website

for maps and graphs, showing real-time

streamflow conditions in the United

States and Puerto Rico. Located at http://

water.usgs.gov/waterwatch/, WaterWatch

maps depict current streamflow as colorcoded dots at about 3,000 streamgages.

The colors represent percentiles of

streamflow that are calculated from

historical observations for the current day

of the year. Only stations having at least

30 years of continuous record are used to

ensure that the calculated percentiles are

representative of historical conditions.

Seven categories of streamflow are

shown on WaterWatch maps: new record

high for the day (black); ≥90th percentile

(dark blue); 75th-89th percentile (light

blue); 25th-74th percentile (green); 10th24th percentile (orange); <10th percentile

(brown); and new record low for the day

(red).

A major attribute of WaterWatch is a

point and click feature that allows users

to retrieve maps and graphs of real-time

Additional Information

USGS Water Data

USBR Water Info

USACE Water Conditions

NWS Soild Moisture Info

NWS Snow Information

NRCS Reservoir Info

NWS Water Supply Outlook

USGS Flow Outlook

25th – 74th percentile

10th – 24th percentile

< 10th percentile

New record low

Explanation

New record high

75th – 89th percentile

> 90th percentile

stage and discharge data for individual

stations. Maps of State hydrologic

conditions can be accessed from the

National map, and graphs of recent

streamflow at individual streamgages can

be obtained from State maps. This feature

facilitates rapid assessment of both

general and specific water-resources

conditions. WaterWatch also serves as a

geospatial front end to NWIS-Web, the

new USGS online National Water

Information System that provides access

via home or office computer to real-time

and historical surface-water, groundDry Normal Wet

Real-Time Streamflow

Map - Day of year

Summary - Day of year

Map animation

Flood and high flow map

Daily Streamflow

7-Day g Avera e Streamflow

Below Normal Streamflow

Map - Day of year

Summary - Day of year

Map - All days

Summary - All days

Map - Week of year

Summary - Week of year

Map - All weeks

Summary - All weeks

Map - Week of year

Summary - Week of year

Map - All weeks

Summary - All weeks

State Information

Drought Watch

AK

PR-VI

HI

Choose a data retrieval option and select a location on the map 

❍ List of all stations in state, State map, or ❍ Nearest stations
water, and water-quality data. Access to

data (including real-time streamflow and

historical flood peaks) via NWIS-Web can

be obtained at http://waterdata.usgs.gov/

nwis/. To provide users with a broad

perspective on short-term and long-term

streamflow conditions and variations,

WaterWatch maps and graphs are organized into three distinct categories: realtime, daily, and 7-day average streamflow.

Real-Time Streamflow

The “Real-time streamflow” map

tracks rapid changes in rivers and streams.

The map is refreshed hourly with the data

at each streamgage generally updated

every 4 hours, although during flood

conditions, the map can be updated more

frequently. The general appearance of the

map changes very little from one hour to

the next, however, individual sites may

change rapidly in response to major rain

events or to reservoir releases.

Daily Streamflow

The “Daily streamflow” map depicts

average streamflow during the previous

day. Although similar in appearance to

“Real-time streamflow” maps, "Daily"

maps are less likely to reflect the influence

of short-term events such as reservoir

releases and short-duration precipitation

events.

7-Day Average Streamflow

The “7-day average streamflow” map

shows the average streamflow during the

past 7 days. Averaging streamflow values

over an entire week makes this map more

indicative of persistent streamflow

conditions than either the “Real-time

streamflow” or the “Daily streamflow”

maps. This map also provides a better

indication of the hydrologic response to

prolonged wet and dry periods.

Flood and Drought Flows

In addition to real-time, daily, and

weekly information, specialized maps and

graphs for flood and high flows as well as

drought and low flows are available. The

“Flood and high flow” maps show

streamgage locations where the water level

is currently at or above flood stage

(depicted as a black triangle) or at high

flow (depicted as blue circles). These maps

are based on the flood stages defined by

the National Weather Service (NWS) and

used for flood forecasting purposes. It

should be noted, however, that flood

conditions may be more extensive than

shown on individual flood and high flow

maps because NWS has not identified

flood stages at all USGS streamgaging

sites.

The “Below normal streamflow"

maps show average streamflow conditions for the past 7 days, highlighting

locations that are experiencing low flows

or hydrologic drought. Averaged over an

entire week, these maps are more

indicative of long-term streamflow

conditions than either the “Real-time

streamflow” or the “Daily streamflow”

maps.

Graphs of Recent Conditions

Streamflow variations through time

can be tracked using graphs that depict an

index of average streamflow for each

State and water-resources region. State

and regional index graphs are available

for daily and weekly streamflow conditions. The streamflow index, plotted as a

red line on the graph, is calculated each

day as the average of the streamflow

index values for all streamgages in a

particular State or water-resources region

that have at least 30 years of record.

Index values correspond to the following

streamflow percentiles: 1 represents the

1st percentile (lowest streamflow on

record); 2 is the 2nd to 9th percentiles

(much below normal); 3 is the 10th to

24th (below normal); 4 is the 25th to 74th

(normal); 5 is the 75th to 89th (above

normal); 6 is the 90th to 99th (much

above normal); and 7 is the 100th

percentile (highest streamflow on record).

For each State and region, two index

graphs are depicted–one shows values for

the past 45 days, and the other shows

variations since June 1999.

Map Animations

Daily WaterWatch maps can also be

viewed as animations. The daily maps are

grouped into monthly animations dating

back to June 1999. These animations

provide a useful visual characterization of

streamflow changes from day to day,

particularly in depicting riverine responses to intense precipitation, such as

occurs during tropical storms and

hurricanes. They also facilitate assessment of the speed with which hydrologic

drought can intensify along rivers and

streams.

For further information, please

contact:

Dr. Harry F. Lins

U.S. Geological Survey

National Center, MS-415

12201 Sunrise Valley Drive

Reston, VA 20192

hlins@usgs.gov

Daily average streamflow conditions for the Mid-Atlantic Water

Resources Region from June 22, 1999 to May 21, 2002.

Printed on recycled paper

Since June 22, 1999

Mid Atlantic [248 sites]

Average streamflow index

7

6

5

4

3

2

1 DRY

1999 2000 2001 2002

WET

NORMAL

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