The monitoring network within this area

Hydrionis holds 1,581 values from 10 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

1,581

Values held

1913–2026

Record spans

Gauges within the Los Angeles huc8 subbasin

10 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 ARROYO SECO NR PASADENA CA

The highest instantaneous discharge the publisher recorded in each year — a flood peak as measured, not a daily average of one. 1914–2025.

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	ARROYO SECO NR PASADENA CA (m³/s)
1914	164
1915	18.0
1916	89.2
1918	16.1
1919	2.61
1920	12.7
1921	18.4
1922	10.5
1924	2.29
1925	5.95
1926	41.1
1927	39.6
1928	8.44
1929	4.39
1930	4.05
1931	4.28
1933	0
1934	26.9
1936	20.0
1937	18.1
1938	244
1940	12.8
1941	37.9
1943	160
1944	51.0
1946	19.3
1948	1.27
1949	0.991
1951	0.340
1952	30.9
1954	16.2
1955	3.03
1956	23.1
1957	4.47
1958	20.2
1959	9.94
1960	4.81
1962	42.5
1963	13.1
1964	5.15
1965	5.49
1966	43.3
1967	48.7
1969	242
1970	18.9
1971	6.29
1973	106
1974	11.0
1975	15.1
1976	16.7
1977	6.51
1978	152
1979	5.47
1980	87.2
1981	17.8
1982	17.4
1983	74.8
1984	3.94
1986	6.03
1987	0.368
1988	12.9
1990	4.62
1991	26.1
1992	48.4
1993	48.4
1994	3.65
1995	49.0
1996	16.5
1998	124
1999	1.76
2000	14.4
2001	9.85
2002	1.16
2003	12.3
2004	20.0
2005	100
2006	31.7
2007	0.340
2008	25.3
2009	7.65
2010	131
2012	6.43
2014	23.6
2015	38.5
2016	6.00
2017	26.0
2018	4.22
2019	28.2
2020	14.3
2021	1.71
2023	33.1
2024	15.3
2025	8.47

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	1914–2025
Completeness	83.0% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	19 separate periods inside 1914–2025 hold no value. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1914 and is not continuous from it: 112 years separate the first value from the last, and 83% 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 ARROYO SECO NR PASADENA 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. 1914–2025.

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	ARROYO SECO NR PASADENA CA (mm)
1914	989
1917	126
1918	176
1919	45.0
1920	101
1921	334
1922	550
1923	62.0
1924	25.0
1925	32.0
1926	189
1927	203
1928	32.0
1929	38.0
1930	49.0
1931	59.0
1932	140
1933	95.0
1934	167
1935	181
1936	135
1937	334
1938	703
1939	88.0
1940	126
1941	759
1942	52.0
1943	659
1944	428
1945	165
1946	208
1947	79.0
1948	33.0
1949	44.0
1950	38.0
1951	35.0
1952	339
1953	30.0
1954	90.0
1955	38.0
1956	63.0
1957	51.0
1958	325
1959	45.0
1960	33.0
1961	19.0
1962	194
1963	56.0
1964	41.0
1965	336
1966	284
1967	448
1968	97.0
1969	1,263
1970	157
1971	95.0
1972	33.0
1973	246
1974	153
1975	75.0
1976	74.0
1977	71.0
1978	791
1979	176
1980	650
1981	70.0
1982	231
1983	868
1984	85.0
1985	52.0
1986	140
1987	50.0
1988	100
1989	39.0
1990	21.0
1991	110
1992	443
1993	909
1994	60.0
1995	539
1996	172
1997	95.0
1998	612
1999	47.0
2000	88.0
2001	96.0
2002	17.0
2003	67.0
2004	135
2005	1,043
2006	144
2007	18.0
2008	173
2009	77.0
2010	392
2011	332
2012	73.0
2013	30.0
2014	45.0
2015	32.0
2016	35.0
2017	132
2018	34.0
2019	189
2020	71.0
2021	48.0
2022	29.0
2023	399
2024	223
2025	135

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	1914–2025
Completeness	98.2% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	One period inside 1914–2025 holds no value: 1915 to 1916, 2 years with no reading. It is drawn as a break in the line and is never interpolated across.
Continuity	The record begins in 1914 and is not continuous from it: 112 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 Los Angeles and what each holds
Gauge	Measures	Values	Record
ARROYO SECO NR PASADENA CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	370	1913–2026
BIG TUJUNGA C NR SUNLAND CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	214	1916–2026
PACOIMA C NR SAN FERNANDO CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	211	1916–2026
LOS ANGELES R A LONG BEACH CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	203	1929–2026
SANTA ANITA C NR SIERRA MADRE CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	198	1916–2026
RIO HONDO NR DOWNEY CA	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	188	1928–2026
LOS ANGELES R A LOS ANGELES CA	catchment area, annual maximum river flow	51	1930–2026
LOS ANGELES R NR DOWNEY CA	catchment area, annual maximum river flow	50	1928–2026
RIO HONDO NR MONTEBELLO CA	catchment area, annual maximum river flow	49	1928–2026
LITTLE SANTA ANITA C NR SIERRA MADRE CA	catchment area, annual maximum river flow	47	1916–2026

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 — 18070105. 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
ARROYO SECO NR PASADENA 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
BIG TUJUNGA C NR SUNLAND 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
PACOIMA C NR SAN FERNANDO 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
LOS ANGELES R A LONG BEACH 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
SANTA ANITA C NR SIERRA MADRE 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
RIO HONDO NR DOWNEY 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
LOS ANGELES R A LOS ANGELES 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
LOS ANGELES R NR DOWNEY 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
RIO HONDO NR MONTEBELLO 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
LITTLE SANTA ANITA C NR SIERRA MADRE 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	8	yes, 3 or more
Years spanned	114	yes, 20 or more
Values held	1,581	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-11098000.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), Los Angeles gauge records, accessed 2026-10-05, hydrionis.com/waters/united-states-los-angeles/

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 Los Angeles 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 confidence2025-02-13

Source: USGS — National Water Information System, USGS site 11098000, 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.