Water Storage for Agriculture

Transcription

1 Water Storage for Agriculture Ted van der Gulik, P.Eng. Partnership for Water Sustainability in BC

2 Water Storage Options Dam! usually constructed within a watercourse! must follow the dam safety regulation! requires a storage licence Dugout constructed with a berm! adhere to the dam safety regulation! may or may not require a water licence! Dugout without a berm! licence requirements will depend on water source and size of reservoir!

3 Dam Safety Regulation Why?

4 Dam Failure Modes Downstream slide due to weak foundation Upstream slide due to sudden drawdown Downstream slide weak embankmant Flow slide in loose sand and silt

5 Dam Safety Regulation Applies to the following:! > 1m > 1,000,000 m3 storage! > 2.5 m > 30,000 m3 storage! > 7.5 m any volume of storage Or any facility with significant downstream consequence

6 Dam Components Cross section - dam crest is a minimum of 3 m

7 Dam Components Sluiceway - the sluice must be encased in concrete - there must be cutoff collars installed on the sluice

8 Dam Components Sluiceway - proper drainage must carry discharge away from the toe of the dam

9 Dam Components Spillway - must be constructed in undisturbed ground around the dam - a freeboard of 1 m is required from the top of dam to the spillway sill

10 Dam Components Spillway boom - is required to prevent debris from entering and plugging the spillway

11 Dam Components Sluice box - control must be on the upstream side of dam

12 Dam Components Wetland meadow sluice box - for small facilities

13 Sluice box issues Dam Maintenance and Issues

14 Spillway overgrowth Dam Maintenance and Issues

15 Dam Reservoir Scenario 40 acre farm:! annual water requirements is 40 acre ft; 50,000 m3! mimimal stream flow requires all of the water to be stored! a dam is constructed on a small 10 acre meadow! a 2.25 m dam is constructed allowing 1 m of freeboard! total storage is 50,000 m3! cost will depend on length of dam, outlet works etc. - can easily exceed $100,000 - $200,000

16 Licence and Permit Costs 40 acre field with a storage facility Storage licence! application fees $150.00! application for permit to occupy crown land $500! annual storage fee $25 - $50 Irrigation licence! irrigation application fee $150.00! irrigation licence - $30 - $50

17 BC Dugout Guide

18 Dugout Dugout considerations:! dugouts do not require a licence if water is collected from runoff on you property! water is often pumped directly from a dugout! they usually require supplemental flows to be effective! as a rule they are safer facilities! water quality can deteriorate more quickly than larger reservoirs

19 Basic Dugout Considerations: Dugout options

20 Dugout Design Features

21 Considerations: Dugouts with Berms! may be required to follow the same rules as dams! downstream considerations will be important! will require a spillway to prevent overtopping! a sluiceway is not required and would be costly! Dugout depth is limited to the pump capability

22 Dugout intake considerations! Centrifugal pumps can only lift 3.5 m! A submersible pump will need to be used for deeper dugouts! There will always be dead water that cannot be accessed! A power source will need to be close by single phase will be sufficient in most instances

23 Dugout intake system

24 Solar intake system Practical for:! stockwatering! drip systems for small areas (gardens, flower beds etc.)! small greenhouses

25 Dugout Maintenance

26 Dugout Maintenance

27 Dugout Maintenance! Copper Sulphate Treatment! Water cannot be discharged to a stream!!

28 Dugout sealing Clay Lining! Spread a layer of clay along the bottom of the dugout specialized equipment is used to compress the clay into an impervious layer. Bentonite! Bentonite is an expandable clay that can be mixed with the soil. Once wetted it expands to form a seal Sodium Chloride Additive! If the soil is more than 20% clay sodium chloride can be added to produce a seal. Soil testing is required to determine the amount of sodium chloride required for the clay content

29 Dugout sealing Plastic Liners! Plastic liners are good but expensive and must be ultraviolet resistant to last for a long time! Liners are available in various thicknesses! Manufacturer s directions should be followed for proper installation! Drains may be required to prevent lifting due to hydraulic pressure. Gleization! Gleization involves covering the bottom with 6 inches of chopped straw. This layer is covered with 6 inches of clay and compacted.! As the straw decomposed under anaerobic conditions it forms a blue grey substance that seals the pores between the soil particles.! This takes a bit of time so water will continue to seep out until this layer forms.

30 Evaporation loss will vary on:! Wind and local climatic conditions! Reservoir size! Water temperature. Dugout Evaporation Loss

31 Dugout Scenario 1 5 acre vegetable farm on drip supplied by a well producing 5 gpm:! annual water requirements is 4 acre ft; 5,000 m3! assume dugout is filled from runoff prior to irrigation season! well supplies 2700 m3 during the growing season! storage required is 2700 m3 in dugout! dugout size would be 3m x 30 m x 30m! cost will depend on site conditions but is expected to be $20,000

32 Dugout Scenario 2 5 acre grape farm with drip irrigation supplied from a well producing 10 gpm:! annual water requirements is 3 acre ft; 3,700 m3! well supplies 5454 m3 over the 120 day growing season

33 Agriculture Water Demand gpm 7 gpm Apr May Jun Jul Aug Sep Crop demand Irrigation peak flow to match crop Average Irrigation flow over the entire season 5 acre grape farm with drip will require 14 gpm at peak of season Well is producing 10 gpm

34 Dugout Scenario 2 5 acre grape farm with drip irrigation supplied from a well producing 10 gpm:! annual water requirements is 3 acre ft; 3,700 m3! well supplies 5454 m3 over the growing season! peak demand for one month is 14 gpm but well supplies only 10 gpm! dugout must supply one month of supply at 4 gpm! dugout should store 700 m3-3m x 15 m x 15 m