New Exchequer Dam

{{Infobox dam

| name = New Exchequer Dam

| name_official =

| image = Lake_McClure_(822109715).jpg

| image_size =

| image_caption = New Exchequer Dam and Lake McClure viewed from the air

| image_alt =

| location_map =

| location_map_size =

| location_map_caption =

| coordinates = {{coord|37|35|10|N|120|16|10|W|type:landmark|display=inline,title}}

| country = United States

| location = Mariposa County, California

| status =

| construction_began = {{start date and age|1964}}

| opening = {{start date and age|1967}}

| demolished =

| cost =

| owner = Merced Irrigation District

| dam_type = Concrete–faced rockfill{{cite web|url=http://cdec.water.ca.gov/cgi-progs/profile?s=EXC&type=dam|title=New Exchequer–Lake McClure (EXC)|publisher=California Department of Water Resources|work=California Data Exchange Center|date=|accessdate=2012-03-24}}

| dam_height = {{convert|490|ft|m|abbr=on}}{{cite web|url=https://www.federalregister.gov/articles/2012/03/16/2012-6402/merced-irrigation-district-notice-of-application-tendered-for-filing-with-the-commission-and#p-14|title=Merced River Hydroelectric Project Relicensing|publisher=Federal Register|work=Federal Energy Regulatory Commission|date=2012-03-16|accessdate=2012-03-24}}

| dam_height_thalweg =

| dam_height_foundation=

| dam_length = {{convert|1220|ft|m|abbr=on}}

| dam_width_crest =

| dam_width_base =

| dam_volume =

| dam_elevation_crest = {{convert|879|ft|m|abbr=on}}

| dam_crosses = Merced River

| spillway_count = Gated ogee crest

| spillway_type =

| spillway_capacity =

| res_name = Lake McClure

| res_capacity_total = {{convert|1024600|acre.ft|km3}}

| res_capacity_active =

| res_capacity_inactive=

| res_catchment ={{convert|1040.1|mi2|km2|abbr=on}}

| res_surface = {{convert|7147|acre|ha|abbr=on}}

| res_elevation = {{convert|867|ft|m|abbr=on}}

| res_max_depth =

| res_max_length = {{convert|29|mi|km|abbr=on}}

| res_max_width =

| plant_hydraulic_head = {{convert|437|ft|m|abbr=on}}

| res_tidal_range =

| plant_operator =

| plant_commission =

| plant_decommission =

| plant_type =

| plant_turbines =

| plant_capacity = 94.5 MW{{cite web|url=http://www.swrcb.ca.gov/waterrights/water_issues/programs/bay_delta/bay_delta_plan/water_quality_control_planning/docs/hydropower.pdf|title=Appendix X: Hydropower and Electric Grid Analysis of Lower San Joaquin River Flow Alternatives|publisher=California State Water Resources Control Board|work=Evaluation of San Joaquin Flow and Southern Delta Water Quality Objectives and Implementation|date=February 2012|accessdate=2012-03-24}}

| plant_annual_gen = 279,065,000 KWh (2001–2012){{cite web|url=http://www.energy.ca.gov/almanac/renewables_data/hydro/index.php|title=California Hydroelectric Statistics & Data|publisher=California Energy Commission|date=|accessdate=2018-04-26|archive-date=2018-02-26|archive-url=https://web.archive.org/web/20180226135225/http://www.energy.ca.gov/almanac/renewables_data/hydro/index.php|url-status=dead}}

| website =

| extra =

}}

New Exchequer Dam is a concrete–faced, rock-fill dam on the Merced River in central California in the United States. It forms Lake McClure, which impounds the river for irrigation and hydroelectric power production and has a capacity of more than {{convert|1000000|acre feet|km3}}. The Merced Irrigation District (MID) operates the dam and was also responsible for its construction.

Built between 1964 and 1967, the dam replaced the old arch type Exchequer Dam and stands {{convert|490|ft|m}} high. At the time of completion, it was the largest dam of its kind in the world. The dam is named for the town of Exchequer which now lies under the reservoir, while the reservoir is named for Wilbur F. McClure, the State Engineer of California during construction.

History

In 1926, after five years of planning and construction, MID completed the Exchequer or "Great Exchequer" Dam{{cite journal

|author=

|title=Huge Dam to Form Mountain Lake for Water and Power

|journal=Popular Science

|volume=180

|number=5

|year=1926

|page=43}} across the Merced River six miles (9.7 km) above the town of Merced Falls. The dam was a concrete gravity–arch structure {{convert|326|ft|m}} high, holding a {{convert|14|mi|km|adj=on}} lake with a capacity of {{convert|281000|acre feet|m3}} of water. Although the dam was to serve primarily for irrigation, power production began ceremoniously on June 23, 1926 with a press of a telegraph key by President Calvin Coolidge, starting the turbines at a 31 megawatt hydroelectric plant.{{cite web

|url = http://www.mercedid.org/historyofthedistrict

|title = History of the District

|publisher = Merced Irrigation District

|accessdate = 2012-03-25

|url-status = dead

|archiveurl = https://web.archive.org/web/20120323052041/http://www.mercedid.org/historyofthedistrict

|archivedate = 2012-03-23

}}

File:Plate_XXII_Old_Exchequer_Dam_photo_published_1929.jpg

By the 1950s, it became apparent that the limited storage capacity at Exchequer was no longer enough to serve the needs of farmers in the Merced River valley. A high dam was proposed to be built just downstream, creating a reservoir nearly four times the size of Exchequer.

Construction of New Exchequer Dam began on July 8, 1964, directly downstream from the old concrete arch dam. Tudor Engineering Company of San Francisco was responsible for the design of the new dam.{{cite journal

|title=Old dam topped by water flowing to successor

|journal=Popular Science

|year=1966

|page=119

|volume=189

|number=3}} The dam wall was constructed in vertical zones, which consisted of compacted, alternating layers of coarse and fine material ranging in thickness from {{convert|1.6|to|66|ft|m}}.{{cite book

|author=Tančev, Ljubomir

|title=Dams and Appurtenant Hydraulic Structures

|publisher=Taylor & Francis

|year=2005

|isbn=90-5809-586-X

|page=279}} The old Exchequer Dam was incorporated as an upstream toe to help support the rock-fill embankment, which was then armored with a layer of reinforced concrete.{{cite journal

|title=Merced River Development Project

|journal=Journal of the Surveying and Mapping Division

|volume=94–95

|year=1968

|number=1

|pages=203–205}} The dam was topped out in early 1967 and the power plant went into commercial operation by July.

As the new reservoir filled, it inundated an additional {{convert|15|mi|km}} of the Merced River canyon and buried sections of the historic Yosemite Valley Railroad and the mining town of Bagby under {{convert|50|ft|m}} of water.{{cite web

|url=http://www.mariposaresearch.net/bagby.html

|title=The Disappearance of Bagby–As told through these newspaper accounts

|publisher=Mariposa County Genealogy & Historical Research

|website=

|accessdate=2012-03-25}} New Exchequer was among the first high concrete–faced rock-fill dams in the world, and its untested design resulted in significant leakage, sometimes up to {{convert|100|cuft/s|m3/s}}. MID began to repair the leaks in the fall of 1985 under orders from the California Division of Safety of Dams.{{cite news

|author=Kane, William D.

|title=Low water level exposing old Exchequer Dam

|work=The Modesto Bee

|date=1985-09-04

}}

The dam has been able to halt major floods in many instances, such as the New Year's Day Flood of 1997. However, it has not always been able to weather the worst droughts – such as in 1977, when the reservoir fell to just {{convert|75000|acre feet|km3}}, a fourteenth of capacity, and in 1991, which saw historic low water levels of {{convert|66100|acre feet|km3}}.{{cite web

|url=http://ca.water.usgs.gov/data/waterdata/99/11269500.html

|title=USGS Gage #11269500 on Lake McClure at Exchequer, CA

|publisher=U.S. Geological Survey

|work=National Water Information System

|date=1926–1999

|accessdate=2012-03-26

|archiveurl=https://web.archive.org/web/20120717041422/http://ca.water.usgs.gov/data/waterdata/99/11269500.html

|archivedate=2012-07-17}} In February 2015, the reservoir reached its lowest level on record, at {{convert|63489|acre feet|km3}} or less than 7 percent of total capacity, due to three years of persistent drought.{{cite web

|url=http://www.mercedid.com/index.cfm/water/drought-watch/

|title=Drought Watch

|publisher=Merced Irrigation District

|date=

|accessdate=2014-12-31}}{{cite web

|url=http://cdec.water.ca.gov/cgi-progs/queryDaily?s=EXC&d=&span=2month

|title=New Exchequer-Lake McClure Reservoir Data for January–February 2014

|publisher=California Department of Water Resources

|work=California Data Exchange Center

|accessdate=2015-02-10}}

Dimensions and usage

Image:Mercedmap-new-01.png

New Exchequer Dam stands {{convert|490|ft|m}} high from the foundations and {{convert|479|ft|m}} above the Merced River. The dam is {{convert|1220|ft|m}} long, {{convert|18|ft|m}} wide at the crest, {{convert|1000|ft|m}} wide at the base and is composed of {{convert|5169000|yd3|m3}} of fill. High water releases are controlled by an ogee-type, gated overflow spillway located about {{convert|2|mi|km}} north of the dam. The dam's power station has a capacity of 94.5 megawatts and generates about 316 million kilowatt hours annually.

The reservoir has a storage capacity of {{convert|1024600|acre feet|km3}}, of which {{convert|350000|acre feet|km3}} is reserved for flood control. At full pool, the reservoir has an elevation of {{convert|867|ft|m}}, with {{convert|7147|acre|ha}} of water and {{convert|82|mi|km}} of shoreline.{{cite web

|url = http://www.friendsoftheriver.org/site/DocServer/Merced_WSRA_designation_and_New_Exchequer_Dam.pdf?docID=5841

|title = Merced National Wild & Scenic River Status and the Merced Irrigation District New Exchequer Dam Project

|publisher = Friends of the River

|date = 2011-03-10

|accessdate = 2012-03-25

|url-status = dead

|archiveurl = https://web.archive.org/web/20150910121520/http://www.friendsoftheriver.org/site/DocServer/Merced_WSRA_designation_and_New_Exchequer_Dam.pdf?docID=5841

|archivedate = 2015-09-10

}} To fulfill downstream flood control requirements, the reservoir will only be allowed to rise into the flood-control pool if the flow downstream at Stevinson is forecast to exceed {{convert|6000|cuft/s|m3/s}}.{{cite web

|url = http://www.auburndamcouncil.org/pages/pdf-files/3-cv_floodmgmt_system.pdf

|title = Chapter 3: Central Valley Flood Management Systems

|publisher = Auburn Dam Council

|work = Post–Flood Assessment for 1983, 1986, 1995, and 1997

|accessdate = 2012-03-25

|page = 37

|url-status = dead

|archiveurl = https://web.archive.org/web/20160311201335/http://www.auburndamcouncil.org/pages/pdf-files/3-cv_floodmgmt_system.pdf

|archivedate = 2016-03-11

}}

MID has proposed raising the spillway gates of the dam, which would provide up to {{convert|70000|acre.ft|km3|abbr=on}} of additional storage. However, this has met with controversy because it would result in part-time flooding of a portion of the Merced River designated Wild and Scenic.{{cite web|url=http://www.mercedid.org/_images/69_spillway%20modification%20fact%20sheet.pdf

|title=New Exchequer Dam Spillway Modification Project Fact Sheet

|publisher=Merced Irrigation District

|date=

|accessdate=2011-08-01}} Opponents also point out that the raise is unnecessary, since the reservoir has never overflowed due to flooding since its completion in the mid-1960s.{{cite web

|url=http://www.americanwhitewater.org/content/Article/view/id/31645/

|title=Bill To Roll Back Merced Wild And Scenic Boundary Reintroduced (CA)

|publisher=American Whitewater

|website=

|author=Hooker, Megan

|date=2013-03-15

|accessdate=2014-03-16}}

Lake McClure is also extensively developed for recreational activities, with 515 campsites, four boat ramps and two marinas. In 1992, the lake received 606,000 visitor-days, mostly from May to September.{{cite web

|url=http://www.sjrg.org/EIR/final_pdf/tx3_8.pdf

|title=Affected Environment: Recreation

|publisher=San Joaquin River Group Authority

|work=Administrative Final EIS/EIR

|date=1999-01-28

|accessdate=2012-08-26}}