The monitoring network within this area

Hydrionis holds 1,326 values from 4 gauges within it. Discharge is a property of a gauge and its reach, not of this drainage area, so this page reports the network and its records rather than a single figure.

Gauges

1,326

Values held

1901–2026

Record spans

Gauges within the Upper Merced huc8 subbasin

4 monitoring points, positioned as the publisher records them.

Flood peaks, as measured

This gauge's flood record, as measured. Unlike a daily mean it is the discharge at the moment the river was highest, which is the figure flood frequency analysis is built on.

Largest measured flow of each year at MERCED R A HAPPY ISLES BRIDGE NR YOSEMITE CA

The highest instantaneous discharge the publisher recorded in each year — a flood peak as measured, not a daily average of one. 1916–2025.

Show relevant events (1 event)Shading marks when something was recorded, not what caused the line.

Published by the gauge's own operator from its sub-daily record; Hydrionis stores the figure rather than recomputing it. A year the gauge did not cover produces no value rather than a low one, and the gaps are stated below the chart. A peak is a property of this gauge and its reach: a larger flood upstream or downstream of it is not in this series.

What the shaded periods are (1 event)

A shaded period marks when something was recorded, not what caused the shape of the line. Where the two coincide, they coincided.

Documented record — A documented event, compiled from cited sources after it happened. The dates are as good as the record, which for older events can mean the month rather than the day.

Event	Type	Period	Standing	Authority
Hurricane Katrina water and sanitation collapse	Flood	2005-08-29 – 2005-09-30	Documented record	Compiled record

Not shown on this chart

The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.

View the data behind this chart

Underlying data
Period	MERCED R A HAPPY ISLES BRIDGE NR YOSEMITE CA (m³/s)
1916	70.8
1917	94.0
1918	90.0
1919	108
1920	77.0
1921	77.0
1922	91.7
1923	74.2
1924	35.1
1925	74.2
1926	63.4
1927	79.9
1928	58.0
1929	71.4
1930	53.0
1931	38.2
1932	72.8
1933	71.4
1934	26.5
1935	79.9
1936	67.4
1937	85.5
1939	34.3
1940	74.2
1941	91.2
1942	79.3
1943	98.5
1944	56.1
1945	86.1
1947	69.4
1948	87.2
1949	70.2
1950	71.4
1952	101
1953	61.7
1954	70.8
1955	79.3
1957	82.4
1958	103
1959	43.0
1960	48.4
1961	30.6
1962	63.1
1963	147
1964	48.7
1966	46.4
1967	131
1968	41.9
1969	141
1970	66.0
1971	61.4
1972	76.2
1973	120
1974	92.3
1975	132
1976	40.8
1977	51.0
1978	119
1979	99.1
1980	114
1981	59.5
1982	138
1983	154
1984	81.0
1985	45.3
1986	114
1987	49.6
1988	46.4
1989	54.1
1990	30.9
1991	65.4
1992	42.2
1993	88.9
1994	53.0
1995	148
1996	167
1997	286
1998	118
1999	79.6
2000	82.7
2001	66.0
2002	64.8
2003	129
2004	51.8
2005	161
2006	123
2007	33.4
2008	78.2
2009	77.9
2010	127
2012	63.7
2013	49.6
2014	33.7
2015	25.0
2016	70.5
2017	148
2018	228
2019	120
2020	61.2
2021	39.9
2023	141
2024	84.4
2025	68.0

About this series

Everything below is a property of the data rather than a rating of it. There is deliberately no single confidence score: how much a gap matters depends on what you are about to do with the series, and only you know that.

Source	United States Geological Survey — National Water Information System · US Government work — public domain
How the values came to exist	Measured
Period held	1916–2025
Completeness	93.6% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	7 separate periods inside 1916–2025 hold no value. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1916 and is not continuous from it: 110 years separate the first value from the last, and 94% of the years between them are held. The span is not the record.
Last read from the publisher	2026-10-01
Redistribution	Permitted by the upstream licences
Commercial reuse	Permitted by the upstream licences. No Hydrionis access tier can widen this.
Methodology	How this was produced

How much of the rain came back out

A discharge in cubic metres per second cannot be compared with anything: the larger number may only mean the larger catchment. Divided by the area draining to the gauge it becomes a depth of water over that land, which answers a question a reader already has — of the rain that fell here, how much came back out as river?

Water leaving the catchment above MERCED R BL MERCED FALLS DAM NR SNELL CA, as a depth

The year's flow spread over the land draining to this gauge, in millimetres — the same unit rainfall is measured in. 1902–2024.

Show relevant events (1 event)Shading marks when something was recorded, not what caused the line.

Computed by Hydrionis from the published annual mean flow and the catchment area the station's own publisher states. It is not a water balance: the difference between rainfall and runoff is not evaporation alone but also change in groundwater storage, water abstracted and taken elsewhere, and water imported by transfer schemes — which is why a catchment can yield more runoff than the rain that fell on it without anything being measured wrongly. A different area figure rescales every value here by the ratio between them.

What the shaded periods are (1 event)

A shaded period marks when something was recorded, not what caused the shape of the line. Where the two coincide, they coincided.

Documented record — A documented event, compiled from cited sources after it happened. The dates are as good as the record, which for older events can mean the month rather than the day.

Event	Type	Period	Standing	Authority
Hurricane Katrina water and sanitation collapse	Flood	2005-08-29 – 2005-09-30	Documented record	Compiled record

Not shown on this chart

The 1976 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
The 2022 drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Yorkshire drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cantareira water crisis, São Paulo — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
Cape Town Day Zero — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.
European drought — This event’s area does not contain this chart’s subject. Sharing a country is not sharing an event, so it is not drawn.

View the data behind this chart

Underlying data
Period	MERCED R BL MERCED FALLS DAM NR SNELL CA (mm)
1902	321
1903	434
1904	554
1905	340
1906	923
1907	944
1908	228
1909	723
1910	433
1911	948
1912	225
1916	676
1917	480
1918	399
1919	299
1920	340
1921	447
1922	650
1923	400
1924	122
1925	399
1926	273
1927	464
1928	329
1929	225
1930	229
1931	116
1932	469
1933	255
1934	161
1935	496
1936	516
1937	557
1938	884
1939	268
1940	481
1941	610
1942	582
1943	593
1944	319
1945	483
1946	433
1947	252
1948	295
1949	291
1950	455
1951	408
1952	676
1953	291
1954	307
1955	295
1956	642
1957	325
1958	594
1959	233
1960	220
1961	139
1962	398
1963	430
1964	230
1965	589
1966	167
1967	597
1968	300
1969	893
1970	377
1971	289
1972	368
1973	355
1974	466
1975	505
1976	273
1977	117
1978	551
1979	456
1980	721
1981	311
1982	817
1983	1,225
1984	508
1985	327
1986	498
1987	273
1988	229
1989	221
1990	170
1991	196
1992	209
1993	391
1994	309
1995	793
1996	575
1997	735
1998	787
1999	395
2000	426
2001	324
2002	299
2003	325
2004	316
2005	565
2006	760
2007	333
2008	265
2009	295
2010	379
2011	825
2012	300
2013	250
2014	167
2015	83.0
2016	243
2017	978
2018	360
2019	689
2020	314
2021	227
2022	215
2023	950
2024	403

About this series

Source	United States Geological Survey — National Water Information System · US Government work — public domain
How the values came to exist	Derived Computed by Hydrionis
Period held	1902–2024
Completeness	97.6% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	One period inside 1902–2024 holds no value: 1913 to 1915, 3 years with no reading. It is drawn as a break in the line and is never interpolated across.
Continuity	The record begins in 1902 and is not continuous from it: 123 years separate the first value from the last, and 98% of the years between them are held. The span is not the record.
Inputs last read	2026-10-01 · when the records this was computed from were last read from their publishers
Calculation date	2026-08-24 · when the calculation method was last versioned, not a reading of any publisher
Redistribution	Permitted by the upstream licences
Commercial reuse	Permitted by the upstream licences. No Hydrionis access tier can widen this.
Methodology	How this was produced

Every gauge Hydrionis holds within this area

Gauges within the Upper Merced and what each holds
Gauge	Measures	Values	Record
MERCED R BL MERCED FALLS DAM NR SNELL CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	380	1901–2026
MERCED R A HAPPY ISLES BRIDGE NR YOSEMITE CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	367	1915–2026
MERCED R A POHONO BRIDGE NR YOSEMITE CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	364	1916–2026
MERCED R A EXCHEQUER CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	215	1901–2026

How these gauges were attached to this water

Assigned by the publisher to a numbered basin Every gauge here is assigned to this drainage area by its own publisher, which issues the area an official code — 18040008. A drainage area is not a river: it contains the tributaries as well as the main channel, and a gauge in it may be on any of them.

What each gauge’s link to this water rests on
Gauge	Evidence	Established
MERCED R BL MERCED FALLS DAM NR SNELL CA	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02
MERCED R A HAPPY ISLES BRIDGE NR YOSEMITE CA	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02
MERCED R A POHONO BRIDGE NR YOSEMITE CA	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02
MERCED R A EXCHEQUER CA	Stated by the publisher — USGS site service, huc_cd field — https://waterservices.usgs.gov/nwis/site/ ; named from the USGS Watershed Boundary Dataset 8-digit HU (Subbasin) layer — https://hydro.nationalmap.gov/arcgis/rest/services/wbd/MapServer/4	2026-10-02

What this record holds

Hydrionis decides which waters get a page, and which of those are offered to search, from what is actually held rather than from how the page reads. Five signals are counted; this record has 5 of them, which makes it a full profile.

Information-gain signals held for this water body
Signal	Held	Counts
Gauges holding a real record	4	yes, 3 or more
Years spanned	126	yes, 20 or more
Values held	1,326	yes, 1000 or more
Distinct measurements	5	yes, 2 or more
Publishers measuring it	2	yes, 2 or more
Official identifiers	1	recorded, not counted

Use this data

Machine-readable JSON /api/v1/observations/by-subject/gauge-usgs-11270900.json
How to cite this, and who you must credit
How these figures were produced
Request this at a different scale, format or geography

No bulk download is offered here, which is a licence position rather than a product one: at least one contributing publisher does not permit redistribution. The values can be read on the page, cited, and pointed to at source.

Attribution and citation

Suggested citation for Hydrionis

Hydrionis (2026), Upper Merced gauge records, accessed 2026-10-05, hydrionis.com/waters/united-states-upper-merced/

Cite Hydrionis where you rely on values Hydrionis computed, on the method that produced them, or on the compilation itself. The underlying measurements remain the publishers’ and their attribution requirements apply to you directly.

Recommended, not required. Hydrionis does not claim rights over unmodified public data it relayed, and doing arithmetic on somebody else’s measurements does not make them Hydrionis’s. Cite the version and the access date: the Upper Merced gauge records changes as publishers release and as methods are revised, and a citation without both cannot be checked later. Full guidance is on cite and reuse.

None of the contributing licences requires attribution. Crediting the publishers is still good practice and they are listed above.

Where these figures come from

MeasuredHigh confidence2025-08-12

Source: USGS — National Water Information System, USGS site 11270900, annual peak streamflow. Licence: Open.

Method: The instantaneous maximum discharge of each water year as published by USGS, dated to the day it occurred. One value per October-to-September water year; where the publisher lists both a systematic and a historic peak for a year, the larger is the annual maximum. Values the publisher marks as maximum daily averages are not held here, because they are not instantaneous peaks. Values marked as bounded rather than measured are held as censored observations carrying the bound. Cubic feet per second are converted to cubic metres per second and the publisher unit is recorded alongside.

Rating curves are extrapolated at extreme discharges, so the largest values in a peak series carry the largest measurement uncertainty. Data from the U.S. Geological Survey National Water Information System, a work of the United States government and therefore in the public domain.

Retrieved 1 October 2026.