Agricultural Water Use Efficiency: How Much Water Really Can Be Saved? CGS-West Conference

Transcription

1 Agricultural Water Use Efficiency: How Much Water Really Can Be Saved? CGS-West Conference David Zoldoske, Director (CIT) California State University, Fresno

2 Key Definitions a) Recoverable fractions b) Irrecoverable fractions c) Beneficial consumptive use d) Non-beneficial consumptive use e) New Water 2

3 Estimates on Ag Water Savings Vary Widely: Let s look behind the numbers! A widely distributed report in 2009 suggested a conservative estimate of 4.53 million ac/ft. could be saved (from 34 million ac/ft applied) if farmers were to implement efficient irrigation technologies and improved irrigation scheduling in California 3

4 How Were the Numbers Developed: Improved Irrigation Scheduling The report used 1997 survey data of 55 growers who used CIMIS to help schedule irrigation events. They reported an average water savings of 13% A 2002 DWR report that indicated 20% of growers were using CIMIS to schedule irrigation events 13% * 80% * 32.7MAF = 3.4MAF/annual savings 4

5 How Were the Numbers Developed: Improved Irrigation Technology The report suggested that changing from flood irrigation to sprinkler/drip will provide an additional 1.13 million ac/ft. of water savings. Their data suggests 20% of all surface irrigation acreage in California is wild flooding and only 60% efficient. This number tends to over-estimate and inflate potential water savings from technology. Definition: Uncontrolled or Wild Flooding. Water that is turned into a field without any flow control such as furrows, boarders or corrugations. 5

6 Reported Potential Savings 3.4MAF + 1.1MAF = 4.53MAF 6

7 7 Paper available at: Californiawater.org

8 Ag Water Use in California: A 2011 Update (Summary) Potential new water obtained from ag water use efficiency is 1.3% (330,000 ac/ft) of current amount use by farmers Previous reallocations of ag water supplies (transfers) to the environment (about 5%) Groundwater overdraft of over 2 million ac/ft year is a serious problem Any changes to current water use patterns can affect third-party water supplies 8

9 Understanding Recoverable/Irrecoverable is Critical Most of the delivered water fractions that are termed irrigation inefficiencies or losses are surface runoff and deep percolation that are picked up and re-used by the farmer, other irrigators, cities, or the environment 9

10 Basin Efficiency Basin irrigation accounts for water used and lost on field and picked up and applied in another, and so on A. Farmer A uses 3 units of water, but is only 33% (on-farm) efficient- 2 units of water leave the farm B. Farmer B uses 2 units of water, but it only 50% (on-farm) efficient- 1 unit of water leaves the farm C. Farmer C uses 1 unit of water and is 100% (on-farm) efficient NOTE: Even thought 6 units of water were applied, only 3 units were used, with no water left over for conservation 10

11 Simple Example Basin Efficiency 10 units water delivered 7 units Etc Per field 10 units applied, 7 units ETc Each field 70% efficient 1 unit deep perc 2 units runoff to next field 8 units water delivered 7 units Etc 1 unit deep perc 2 units runoff to next field 8 units water delivered 7 units Etc 26 units delivered to 3 fields, 21 units ETc Area use efficiency 81% -Deep perc could also be picked up -Final 2 units runoff could be picked up 1 unit deep perc 2 units surface runoff to??? 11

12 Double Counting Water The reality is, over-irrigated water that moves beyond the rootzone can return to the groundwater and is available for reuse. Therefore, no new water is made available through improvements in efficiency when this occurs. If the claims about 4.53 million ac/ft. of potential new water savings were true, it would likely manifest itself in groundwater levels rising and/or increased surface water discharge into the ocean. The contrary is observed, groundwater levels are dropping and rivers are running dry. 12

13 How Were the Numbers Developed: Irrecoverable Fractions The suggests that the only true new water available from improved agricultural water use efficiency will come from Irrecoverable Fractions. That is, saving water that would normally end-up in groundwater where salinity levels exceed normal re-use expectations. These savings are estimated at 0.33 million ac/ft. And this comes at a substantial $Cost$ 13

14 The Difference Defined CIT believes the conservative estimates ignore the reality of basin efficiency where over-applied water typically is reused by someone else, either by reaching the groundwater or surface runoff. The major exception is limited areas overlying groundwater with high salinity content or water that runs into the ocean. 14

15 Water Quality Concerns Degradation of water quality as a third-party impact is probably the most serious aspect of poor on-farm irrigation efficiency. The CIT report identifies this as a major concern. 15

16 Drip Paradox Conjunctive use districts like Consolidated Irrigation District (CID) are negatively impacted by widespread adoption of drip irrigation methods Drip systems are dependent on groundwater pumping and do not contribute to groundwater recharge In Wet years, groundwater is no longer recharged through over-application via the historic flood method 16

17 The Following Information is from: Ruud, NC, T.Harter, GF, Marques, NW Jenkins, JR Lund, Modeling of Friant Water Management and Groundwater, Final Report, US Bureau of Reclamation, 294 pp. 17

18 Unintended Groundwater Exchanges A 2003 model of the Friant Water Management and Groundwater revealed approximately 65,000 to 70,000 AF/yr of unintended groundwater exchange occurs annually. Pixley Irrigation District (PID) is the beneficiary of this exchange and is dependent on groundwater for its major source of irrigation water. 18

19 Ag Water Supply Conjunctive Use Tulare County Tule Groundwater Basin ~ 2,300 km 2 19

20 Water Districts & Lindmore ID Lewis Creek WD Long-term Water Balance Lindsay-Strathmore ID Lower Tule River ID Porterville ID Teapot Dome WD Pixley ID Saucelito ID Terra Bella ID 20 Delano-Earlimart ID

21 Unintended Groundwater Exchanges 21

22 DWR Summary: Water Management Opportunities Water Use Efficiency 5.0 MAF Urban efficiency 2.1 MAF Agricultural efficiency 0.6 MAF (0.33 MAF) Reuse and recycling 1.5 MAF Stormwater capture MAF Conjunctive management and groundwater storage 1.0 MAF Estimated Cost to achieve 6 MAF/$4-7 Billion 22

23 Questions? Thank You!