The monitoring network within this area

Hydrionis holds 391 values from 3 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

391

Values held

1916–2026

Record spans

Gauges within the San Marcos huc8 subbasin

3 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 Blanco Rv at Wimberley, TX

The highest instantaneous discharge the publisher recorded in each year — a flood peak as measured, not a daily average of one. 1925–2025.

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	Blanco Rv at Wimberley, TX (m³/s)
1925	1.36
1926	1,068
1929	3,200
1930	294
1931	371
1932	47.9
1933	16.2
1934	253
1935	416
1936	838
1937	54.1
1938	365
1940	67.1
1941	787
1942	371
1943	84.4
1944	309
1946	238
1948	80.7
1949	614
1950	15.9
1951	53.5
1952	2,690
1953	179
1955	136
1956	38.5
1957	1,773
1958	2,730
1959	73.6
1961	957
1962	371
1963	204
1964	121
1965	467
1967	18.3
1968	515
1969	46.7
1970	241
1972	176
1973	487
1975	220
1976	402
1977	320
1978	87.8
1979	314
1980	46.2
1981	507
1983	90.6
1985	1,252
1986	960
1987	612
1988	620
1989	240
1990	292
1991	92.9
1993	47.0
1995	320
1997	966
1998	660
2000	10.4
2001	3,058
2003	142
2004	242
2006	9.49
2007	1,045
2008	4.56
2009	51.3
2010	193
2011	3.48
2012	121
2013	155
2015	4,955
2017	106
2018	72.8
2019	450
2020	124
2021	20.1
2023	3.26
2024	5.01
2025	75.9

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	1925–2025
Completeness	79.2% of the periods in that span are held. Gaps are drawn as breaks and never interpolated.
Known gaps	20 separate periods inside 1925–2025 hold no value. The longest runs from 1927 to 1928 — 2 years with no reading. They are drawn as breaks in the line and are never interpolated across.
Continuity	The record begins in 1925 and is not continuous from it: 101 years separate the first value from the last, and 79% 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 Blanco Rv at Wimberley, TX, as a depth

The year's flow spread over the land draining to this gauge, in millimetres — the same unit rainfall is measured in. 1929–2025.

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	Blanco Rv at Wimberley, TX (mm)
1929	195
1930	59.0
1931	164
1932	49.0
1933	23.0
1934	58.0
1935	135
1936	177
1937	92.0
1938	154
1939	18.0
1940	67.0
1941	288
1942	115
1943	50.0
1944	175
1945	165
1946	159
1947	96.0
1948	21.0
1949	61.0
1950	24.0
1951	14.0
1952	151
1953	73.0
1954	17.0
1955	17.0
1956	12.0
1957	269
1958	296
1959	120
1960	213
1961	218
1962	49.0
1963	28.0
1964	26.0
1965	240
1966	117
1967	42.0
1968	229
1969	103
1970	160
1971	41.0
1972	87.0
1973	337
1974	97.0
1975	249
1976	219
1977	198
1978	49.0
1979	249
1980	55.0
1981	186
1982	71.0
1983	84.0
1984	38.0
1985	240
1986	259
1987	335
1988	59.0
1989	45.0
1990	67.0
1991	240
1992	452
1993	120
1994	95.0
1995	122
1996	21.0
1997	355
1998	347
1999	51.0
2000	74.0
2001	283
2002	437
2003	146
2004	383
2005	152
2006	23.0
2007	318
2008	27.0
2009	47.0
2010	183
2011	23.0
2012	72.0
2013	72.0
2014	20.0
2015	445
2016	195
2017	83.0
2018	58.0
2019	130
2020	40.0
2021	46.0
2022	15.0
2023	8.00
2024	11.0
2025	12.0

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	1929–2025
Completeness	100.0% of the periods in that span are held.
Continuity	Continuous: every year from 1929 to 2025 is held.
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 San Marcos and what each holds
Gauge	Measures	Values	Record
Blanco Rv at Wimberley, TX	burned area within 50 km, catchment area, annual maximum river flow, mean river flow, mean river flow, water year	330	1924–2026
San Marcos Rv at San Marcos, TX	catchment area, annual maximum river flow	32	1995–2026
San Marcos Rv at Ottine, TX	catchment area, annual maximum river flow	29	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 — 12100203. 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
Blanco Rv at Wimberley, TX	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
San Marcos Rv at San Marcos, TX	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
San Marcos Rv at Ottine, TX	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 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	1	no
Years spanned	111	yes, 20 or more
Values held	391	no
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-08171000.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 Marcos gauge records, accessed 2026-10-05, hydrionis.com/waters/united-states-san-marcos/

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 Marcos 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 confidence2025-06-12

Source: USGS — National Water Information System, USGS site 08171000, 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.