Peak Discharge Data for Estimating 1862 American River Flood
(possible input to a HEC-RAS Model)


This modeling idea came from working on the 2012 CEPSYM when the theme was: The 1861-1862 Floods: Informing Decisions 150 Years Later. I researched several topics when thinking about possible aspects of the 1862 flood for speakers to cover. Estimates of the American River flood-peak discharge made in 1862 were found and the idea evolved to this point.

Gary Estes
CEPSYM Founder

Modeling Idea

The idea is to do HEC-RAS modeling of a bedrock segment of the American River (identified as Folsom canyon in 1862) to estimate the peak discharge of January 10, 1862 flood and use the results to estimate the peak discharge at the USGS Fair Oaks gage downstream. The idea is to use modern modeling tools on the available historic data. Then use the modeling results to evaluate the various peak discharge estimates developed over the past 150+ years by engineers in 1862, U.S. Army Corps of Engineers (USACE), and U.S. Geological Survey (USGS).

Modeling Location

The Folsom canyon is a granite bedrock segment of the American River which runs beside Folsom State Prison and measures about 2.25 miles from Folsom Dam to Rainbow Bridge. The name "Folsom canyon" comes from a description in the 1862 report by Leet and Goddard described below. Canon is the spelling of "canyon" used in 1862 and was usually written as cañon.

Dataset for Modeling

The assembled dataset for the modeling work consists of documents, reports, drawings, and photographs. Below is a List of Dataset Items. Each item can be downloaded separately or the entire dataset can be download as a zip file.

Brief Description of Dataset Items

1862 — Leet and Goddard — Cross-sections in Folsom Canyon

A report written by B.F. Leet, Engineer, and George H. Goddard, Consulting Engineer, in 1862 estimated the peak discharge at three cross-sections along the American River. The report was submitted to the Board of Swamp Land Commissioners in Sacramento in May 1862 which offered engineering solutions to protect Sacramento from American River floods. Maps referenced in the report showing the locations of the cross-sections and the railroad bridge section mentioned below were not found. However, the description by Leet and Goddard is sufficient for locating in Folsom canyon two cross-sections with 1862 high water elevations:

  1. Railroad bridge at Folsom
  2. Stockton mills

Leet and Goddard used the high water mark at the Stockton mills located upstream of the railroad bridge to compute the river channel slope and compute the water velocity to the railroad bridge cross-section.

Leet and Goddard wrote:

At this point we have a very accurate measurement of the canon at the railroad bridge at Folsom, a section of which is presented to your Board.

We have the fall and distance from the Stockton mills above, and the hight [sic] of the floods at both points, from these we have deduced the following tables of velocity and discharge at this point.

The sectional area of canon is only 10,782 feet, and yet, by reason of the great slope of 35.95 feet per mile, 0.0066 per foot giving a velocity of 46.49 feet per second, there was actually discharged the enormous amount of 501,294 cubic feet of water per second.

Table of Folsom Canon by Leet and Goddard

[Source: 1862, Leet & Goddard, Engineers' Report on the Northern Boundary of Swamp Land District No. 2, as printed in Sacramento Daily Union [newspaper], May 16, 1862, page 3, with quotation starting at top of 3rd column from left and down to 6th paragraph from top of column and accessed at California Digital Newspaper Collection]

Stockton mills, Stockton and Coover Mill Site, or Stockton and Coover Stone Stable

The name "Stockton mills" was used by Leet and Goddard to identify a location along the North Fork American River across and down river from where the Folsom State Prison was later built. It was thought to be "the first flour mill on the North American Pacific coast." The stone foundation survived the 1862 flood washing away the mill building which was rebuilt in 1862 and burned down in 1867.

[Source: Sacramento Bee (newspaper), February 10, 1894, page 1, col. 7 according to the John H. Plimpton Research Files titled The American River: 10 Mile Ford to Junction (Volume II) held by the California State Parks Photographic Archives, Sacramento]

In other important documents vital to this modeling project, the names used to identify the surviving mill foundation are the "Stockton and Coover Mill Site" and the "Stockton and Coover Stone Stable." Stockton and Coover were the joint owners of the rebuilt mill in September 1862. We will use "Stockton and Coover stone stable" going forward.

Importance of Cross-section at Stockton and Coover Stone Stable

The Stockton and Coover stone stable is the key physical location for estimating American River flood peak discharges starting in 1862 until the stone foundation was removed by the construction of Folsom Dam in 1950's. This will become clear as you read the documents.

» See dataset for Leet and Goddard (1862) Folsom Canyon Cross-sections

1912 — Givan and Grunsky — Statement

The second vital document providing critical data is the Statement Relating to the Flood Discharge of the American River (October 17, 1912) prepared by A. Givan, City Engineer of Sacramento and C.E. Grunsky, Consulting Engineer. It was submitted to the California Debris Commission and the California State Board of Reclamation.

This document is a wonderful collection of information about the 1862 and 1907 floods on the American River. It was prepared to raise questions about the maximum flood flows possible on the American River beside the City of Sacramento. A proposal was made to move a levee further into the river on the north side of the American River across from the City in District 1000 (Natomas Basin). Sacramento was concerned about the loss of flow capacity and impacts on their levees and future flood impacts by this proposal.

For this modeling project, the most important parts of the Statement are:

» See dataset for Givan and Grunsky (1912) Statement

1951 — Matthai — USGS

Howard F. Matthai, Hydraulic Specialist, U.S. Geological Survey wrote an unpublished internal paper titled: "Revision of Peak Discharge of American River at Fair Oaks, Calif., Mar. 25, 1928" (Dec. 14, 1951). It is filed in the USGS California Water Science Center Field Office, Sacramento under "Fair Oaks gage (USGS 11446500)."

Matthai wrote:

The high-water rating for the Fair Oaks gage is unstable; however, it is the opinion of many engineers who have studied flood flows on the American River that the high-water rating at the Stockton and Coover Stone Stable just upstream from Folsom is permanent. Inflow between these two points is negligible during major flood peaks. [page 1]

Matthai concluded:

An extension of the Stone Stable rating by logarithmic plotting to the stage of the 1862 flood gives a peak discharge for that flood of about 340,000 cfs. [page 3]

» See dataset for Matthai (1951) USGS Internal Paper

2009 — Parrett — USGS

Charles (Chuck) Parrett, Hydrologist, U.S. Geological Survey, California Water Science Center, Sacramento, produced an internal document in 2009 recommending the following:

Given that floods and flood frequency is a major concern on the American River, I recommend that the USGS provide as much information on flood magnitude as we can by providing our best estimate of the 1862 flood peak at Fair Oaks in the USGS Peak Flow File. I further recommend that we use the higher peak from my reconstructed curves (318,000 cfs) as our best value for this discharge and that it be coded as an estimate.

In this document he presents the reasoning for the recommendation.

» See dataset for Parrett (2009) USGS Internal Paper

1941 and 1943 — Bossen — USACE

Three documents written by Leslie E. Bossen, Assistant Engineer, U.S. Army Corps of Engineers, Sacramento District, discuss the historical information used for estimating the 1862 and other floods at four locations.

  1. Fair Oaks gage (USGS)
  2. Folsom Powerhouse gage (U.S. Weather Bureau)
  3. Railroad Bridge at Folsom
  4. Stockton and Coover stone stable

Estimates of the 1862 peak discharge at Fair Oaks gage changes as the data collected from additional floods are considered. No mention is made of the potential impact of hydraulic mining sediment upon the channel being raised or lowered by big floods moving sediment. The research by L. Allan James, Ph.D. needs to be considered. ("Hydraulic Mining Sediment Impacts on American River Channel Morphology and Flood Stages")

Interesting to note that the internal paper by Matthai of USGS did not mention in his analysis the Bossen documents. However, there is a handwritten column headed "Bosson" found on his work page titled "American River — Folsom to Fair Oaks" with peak discharge numbers from Bossen's documents.

Parrett did not have Bossen's papers to read when doing his analysis.

» See dataset for Bossen (1941-3) USACE Documents

1950 — Folsom Canyon Topographic Maps: USBR — Design Data

Topographic maps of Folsom canyon were produced as part of the work to build Folsom Dam. In 1950 the U.S. Bureau of Reclamation produced this document: "Design Data for Preparation of Designs and Estimates for Specification Purposes for Excavation of Tailrace Channel Downstream from the PG&E Diversion Dam and Excavation for Powerplant to Elevation 210 feet" [December 1950].

This document contains drawings, topographic maps, and photographs of the segment of the American River known in 1862 as "Folsom canyon" (cañon) from below Folsom Dam to just beyond the Rainbow Bridge downstream. The topographic maps have 5-foot contours which I understand is good for doing cross-sections for HEC-RAS modeling. Plate No. 7 (USBR Drawing No. 485-218-23) shows the Stockton and Coover stone stable.

The result from this construction was the drilling, blasting, and removal of the granite rock to lower the river bed to enable hydropower generation from Folsom Dam. The bottom of new river bed was a rock channel proposed at 60 feet wide. Based on information from captions on photographs of Folsom canyon from John H. Plimpton's "A Picture History of Folsom Dam 10/2/48-5/5/56" obtained from the Placer County Archives, the river bed was lowered 100 feet at Folsom Dam and gradually lowered until about 10 feet or so lower than natural river bed near about Negro Bar downstream of the Rainbow Bridge.

» See dataset for USBR (1950) Topographic Maps of Folsom Canyon

1951 — Folsom Power Plant Drawings, U.S. Bureau of Reclamation

These two drawings show the location of Folsom canyon and the tailrace channel from Folsom Dam to below the Rainbow Bridge. Drawing No. 485-D-60 shows a "hydraulic gradient" line with elevations. This might assist in estimating the velocity of water flowing in Folsom canyon.

» See dataset for USBR (1951) Folsom Power Plant Drawings

List of Dataset Items

Year Item

Photographs (not found in other documents)


Leet & Goddard [Note: some historic documents show spelling of "Leet" as "Leete"]

B.F. Leet (Engineer), and George H. Goddard (Consulting Engineer)
Report to the Board of Swamp Land Commissioners


Givan & Grunsky

A. Givan (City Engineer of Sacramento) and C.E. Grunsky (Consulting Engineer)
Statement to California Debris Commission and California State Board of Reclamation



Leslie E. Bossen, Assistant Engineer, U.S. Army Corps of Engineers, Sacramento District
1862 Flood on American River


Leslie E. Bossen, Assistant Engineer, U.S. Army Corps of Engineers, Sacramento District
Discharge Rating Curves American River


Leslie E. Bossen, Assistant Engineer, U.S. Army Corps of Engineers, Sacramento District
Flood Crest Jan. 1943 American River



Howard F. Matthai, Hydraulic Specialist, U.S. Geological Survey



Charles (Chuck) Parrett, Hydrologist, U.S. Geological Survey, California Water Science Center, Sacramento, CA


Folsom Canyon Topographic Maps

U.S. Bureau of Reclamation produced this document
USBR — Design Data


U.S. Bureau of Reclamation (USBR)

Folsom Power Plant Drawings

Various Entire dataset [ZIP, 427 MB]

* PDF files require a PDF reader. If your computer does not already have one, you can get Adobe® Reader.