Cy­clones put fo­cus on flood pro­tec­tion

Matamata Chronicle - - What’s On - HUGH VERCOE

Rain, rain, and more rain.

Easter this year saw some con­cen­trated heavy rain fall on the rural land of Pi­ako.

The catch­ment was al­ready sat­u­rated from pre­vi­ous down­falls and we watched as trop­i­cal Cy­clone Cook headed to­wards us.

The farm­ers were cer­tainly con­cerned and the unan­swered ques­tions were, will we just get the rain or will we also have to deal with gale force winds?

Will the cy­clone ac­tu­ally hit us and what sort of dam­age can we ex­pect?

Waikato Re­gional Coun­cil man­ages the two main flood pro­tec­tion schemes in the area, the Wai­hou scheme and the Pi­ako scheme.

The Wai­hou is mainly a river con­trol while the Pi­ako pro­vides land pro­tec­tion es­pe­cially to the very flat ly­ing ar­eas of the Hau­raki plains.

Both sys­tems re­sponded as de­signed but the ma­jor­ity of flood­ing oc­curred to farms in the Pi­ako area.

The Pi­ako River Scheme was con­structed in the 1950/60s with fund­ing from lo­cal landown­ers and the govern­ment of the day.

It in­cludes some 166 kms of stop banks, flood­gates, and pumps, some owned by the scheme while oth­ers are pri­vately owned by the farm­ers.

Many of the as­sets are old and the whole scheme is up for much needed im­prove­ment.

When you drive to Ngatea you can see the vast area of land that make up the plains.

The gra­di­ent is around 1:5000 which does not en­cour­age nat­u­ral flow. The Waitoa and the Pi­ako rivers con­verge at Pate­tonga and even­tu­ally dis­charge into the Hau­raki Gulf.

This in it­self is not sim­ple as each in­com­ing tide forces sea wa­ter back up the rivers slow­ing the nor­mal dis­charge.

When the rain came it was ex­tremely heavy and con­cen­trated. In many ar­eas it over topped the stop banks and flooded the lower farm­ing land.

This was to be expected but many farm­ers noted that some­thing was dif­fer­ent this time.

Ar­eas that hadn’t flooded in

‘‘The Paeroa-Tahuna road to­tally dis­ap­peared un­der one large lake over the whole area with other roads stopped by flood­ing.’’

pre­vi­ous events were now flood­ing and wa­ter in the usual pond­ing ar­eas came up faster and higher.

The Paeroa-Tahuna road to­tally dis­ap­peared un­der one large lake over the whole area with other roads stopped by flood­ing.

Wa­ter that would nor­mally flow through the large Kop­u­atai Peat Dome in the area was no longer flow­ing freely.

Some sug­gested that the re­cent Kaik­oura earth­quake had caused the land to rise over the fault line run­ning through the area.

Oth­ers be­lieved that the farm­ing land sur­round­ing the peat dome had shrunk to a greater level than expected.

Depart­ment of Con­ser­va­tion man­ages the peat dome and some farm­ers be­lieve that DOC has made re­cent change to their man­age­ment of the dome by in­stalling nu­mer­ous weirs to hold wa­ter in all year round.

I guess a de­brief now the rain has gone will an­swer some of the ques­tions as to what was dif­fer­ent this time.

Farm­ers are well known for com­plain­ing about the weather, but this time many of our lo­cal farm­ers face se­ri­ous threats to the short term vi­a­bil­ity of their busi­nesses. We will all feel the fi­nan­cial im­pact.

-Hugh Vercoe is a Wai­hou coun­cil­lor for the Waikato Re­gional Coun­cil.

CHRIS­TEL YARDLEY/FAIRFAX NZ

Roads sur­round­ing Pate­tonga flooded af­ter cy­clones Deb­bie and Cook passed over the re­gion.

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