The monitoring network within this area

Hydrionis holds 376 values from 2 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

376

Values held

1929–2026

Record spans

Gauges within the San Pablo Bay huc8 subbasin

2 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 NAPA R NR ST HELENA CA

The highest instantaneous discharge the publisher recorded in each year — a flood peak as measured, not a daily average of one. 1929–2025.

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	NAPA R NR ST HELENA CA (m³/s)
1929	127
1931	26.1
1940	331
1941	223
1942	334
1943	215
1944	139
1945	129
1947	81.8
1948	65.4
1949	136
1950	139
1952	127
1954	227
1955	357
1957	88.1
1958	273
1959	138
1960	328
1961	61.2
1962	219
1963	348
1964	142
1965	334
1966	260
1967	314
1968	141
1969	187
1970	268
1971	31.7
1973	320
1974	189
1975	242
1976	5.75
1977	3.68
1978	283
1979	70.2
1980	204
1981	104
1983	303
1985	209
1986	479
1987	77.3
1988	39.4
1989	106
1990	38.8
1991	197
1992	81.8
1993	281
1994	25.5
1995	394
1996	164
2001	92.9
2002	289
2003	220
2005	110
2006	38.2
2008	126
2009	79.3
2010	106
2011	208
2012	99.1
2014	62.3
2016	128
2017	264
2018	112
2019	271
2021	5.04
2023	202
2024	150
2025	240

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	1929–2025
Completeness	73.2% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	16 separate periods inside 1929–2025 hold no value. The longest runs from 1932 to 1939 — 8 years with no reading. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1929 and is not continuous from it: 97 years separate the first value from the last, and 73% of the years between them are held. The span is not the record.
Last read from the publisher	2026-08-31
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 NAPA R NR ST HELENA 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. 1930–2025.

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	NAPA R NR ST HELENA CA (mm)
1930	212
1931	157
1940	827
1941	884
1942	627
1943	327
1944	204
1945	419
1946	132
1947	117
1948	178
1949	212
1950	473
1951	410
1952	686
1953	342
1954	396
1955	483
1956	630
1957	228
1958	818
1959	145
1960	270
1961	168
1962	410
1963	504
1964	359
1965	371
1966	433
1967	583
1968	359
1969	808
1970	996
1971	224
1972	146
1973	770
1974	541
1975	423
1976	16.0
1977	75.0
1978	584
1979	301
1980	537
1981	493
1982	848
1983	1,406
1984	201
1985	166
1986	851
1987	167
1988	143
1989	184
1990	97.0
1991	212
1992	205
1993	525
1994	105
2001	361
2002	501
2003	436
2004	445
2005	604
2006	624
2007	119
2008	254
2009	188
2010	500
2011	444
2012	481
2013	42.0
2014	249
2015	81.0
2016	415
2017	957
2018	130
2019	728
2020	47.0
2021	235
2022	105
2023	677
2024	751
2025	481

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	1930–2025
Completeness	85.4% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	2 separate periods inside 1930–2025 hold no value. The longest runs from 1932 to 1939 — 8 years with no reading. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1930 and is not continuous from it: 96 years separate the first value from the last, and 85% of the years between them are held. The span is not the record.
Last read from the publisher	2026-08-24
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 San Pablo Bay and what each holds
Gauge	Measures	Values	Record
NAPA R NR ST HELENA CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow	204	1929–2026
NAPA R NR NAPA CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow	172	1929–2026

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 — 18050002. 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
NAPA R NR ST HELENA 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	2026-08-26
NAPA R NR NAPA 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	2026-08-26

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 3 of them, which makes it a full profile.

Information-gain signals held for this water body
Signal	Held	Counts
Gauges holding a real record	2	no
Years spanned	98	yes, 20 or more
Values held	376	no
Distinct measurements	4	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-11456000.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), San Pablo Bay gauge records, accessed 2026-09-02, hydrionis.com/waters/united-states-san-pablo-bay/

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 San Pablo Bay 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 confidence2025-02-04

Source: USGS — National Water Information System, USGS site 11456000, 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 31 August 2026.