City Locks River Gauge

City Locks River Gauge (HM15ZO)

Location: Richmond, VA 23223
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Country: United States of America
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N 37° 31.52', W 77° 25.241'

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The building before you holds equipment that measures the level of the James River leaving Richmond

How it works:
The gauge is a tube of air with a standard amount of pressure inside. How much the river water rises up the tube determines how much more the air is compressed. That increased pressure can be scaled to indicate the river level.

In the beginning, people just read a numbered gauge, but it was hard to read when there were waves and impossible to observe when there was a flood. You can still see it - on the wall, beside the canal door, at the entrance.

Today the measurements are taken electronically every hour and sent via satellite to the National Weather Service and the US Geological Service. You can access the information at

Why you should care:
River height tells you the amount of water flowing downstream - a measure which affects shipping, recreational boating and fishing. During floods, the gauge indicates how much water will inundate farmland and shoreline businesses downstream and whether to operate the floodwall gate upstream. Note, however, that the river level number is a reference point only and does not mean that the water is that deep at all places.

Tides impact the river level too. The gravity of the moon pulls water from the Chesapeake Bay up the river. This displacement is about a foot and it goes as far as the first set of rapids at the Mayo Bridge. No salt water comes this far however, as it travels along the bottom only as far as the Chickahominy River.

There is another gauge at the Huguenot Bridge. It measures the river entering Richmond at the Fall Line - the stretch of rocks and rapids between Bosher Dam and the Mayo Bridge. There are other gauges located up and down the river.

A Brief History:
·1882 monitoring began here by reading the numbered scale attached to the canal entrance
·1957 a structure was built and an electronic system was installed using a float in a tube
·1969 everything was destroyed in the flood — from Hurricane Camille (28.6 feet)
·1971 the highest flood ever recorded took place — from Hurricane Aqnes (36.5 feet)
·1985 the most recent big flood — from Hurricane Juan (30.7 feet)
·2005 the float gauge was replaced by the pressurized system
?and now you are here!
HM NumberHM15ZO
Placed ByFriends of James River Park
Marker ConditionNo reports yet
Date Added Thursday, September 4th, 2014 at 9:17am PDT -07:00
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Locationbig map
UTM (WGS84 Datum)18S E 286091 N 4155905
Decimal Degrees37.52533333, -77.42068333
Degrees and Decimal MinutesN 37° 31.52', W 77° 25.241'
Degrees, Minutes and Seconds37° 31' 31.20" N, 77° 25' 14.46" W
Driving DirectionsGoogle Maps
Area Code(s)757, 804
Closest Postal AddressAt or near 111 Pear St, Richmond VA 23223, US
Alternative Maps Google Maps, MapQuest, Bing Maps, Yahoo Maps, MSR Maps, OpenCycleMap, MyTopo Maps, OpenStreetMap

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