Ed­u­ca­tion day on avoid­ing pond fail­ure

South Waikato News - - NEWS -

How to avoid ef­flu­ent ponds leak­ing or even col­laps­ing is the topic of an ed­u­ca­tion day be­ing run by Waikato Re­gional Coun­cil, along with Deb­bie Care of AgVice.

‘‘Such fail­ures can cause pol­lu­tion of wa­ter­ways and ground­wa­ter, and mean that valu­able nu­tri­ents are lost to farm­ing sys­tems,’’ coun­cil’s proac­tive mon­i­tor­ing man­ager Ross Wight­man said.

‘‘Our ed­u­ca­tion day at Pu­taruru will of­fer a lot of prac­ti­cal ad­vice about how to avoid pond fail­ures.’’

South Waikato pond fail­ures will be dis­cussed, as will the de­sign con­sid­er­a­tions to take into ac­count when con­struct­ing new ef­flu­ent stor­age.

‘‘There are of­ten no warn­ing signs when an ef­flu­ent pond fails but the risk of fail­ure can be min­imised if the pond has been con­structed and main­tained cor­rectly,’’ Wight­man said.

In the South Waikato, a pond fail­ure oc­curred with­out warn­ing in mid-2012. The pond was con­structed in a fri­able rhy­o­lite soil.

Ef­flu­ent ‘’’tun­nelled’’ through the pond wall and caused a sig­nif­i­cant dis­charge of ef­flu­ent into wa­ter and con­tam­i­nated a nearby wa­ter sup­ply.

This pond fail­ure high­lights how farm­ers need to take spe­cial care when con­struct­ing hold­ing fa­cil­i­ties on rhy­o­lite, Wight­man said.

‘‘ Vol­canic rhy­o­lite soil can be found through­out the South Waikato and Taupo as a non-welded, grav­elly and sandy pumice soil, or as a dense welded rock. Rhy­o­lite soils are com­mon in the Waikato through the Taupo vol­canic zone that stretches from Mt Ruapehu to White Is­land,’’ he said.

‘‘ The risk of pond fail­ure can be min­imised dur­ing the de­sign and con­struc­tion phase by en­sur­ing that the pond is con­structed of an ap­pro­pri­ate ma­te­rial, that it is lined cor­rectly, and that the lo­ca­tion is struc­turally sta­ble.

‘‘Also, when con­struct­ing a new ef­flu­ent pond or as­sess­ing an ex­ist­ing one, it is very im­por­tant to un­der­take a thor­ough site in­ves­ti­ga­tion to as­sess the soil pro­file and slope sta­bil­ity.’’

The ef­flu­ent ed­u­ca­tion field day will run from 10.15am to 1.30pm on April 30 at Jack and El­iz­a­beth Scheres’ property on 169 Les­lie Rd, Pu­taruru, Fon­terra sup­ply num­ber 77783. Tea, cof­fee and lunch pro­vided.

For fur­ther in­for­ma­tion and to reg­is­ter for the ed­u­ca­tion day call Ka­t­rina Daysh on 0800 800 401.

Not good: This is an ex­am­ple of what hap­pens when ponds fail in ar­eas with pumice soils. Here ef­flu­ent has breached the pond wall and flowed over­land to a stream near Ti­rau.

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