The three women pulled the horses to safety at the top of the stock banks, where the water had risen to cover it halfway.
Hawke's Bay Regional Council (HBRC) staff were able to mechanically open the river mouth at Clive yesterday to release the floodwaters.
An HBRC representative said they had been aware that the opening at the river mouth has not been ideal for a few weeks but the conditions meant that a new opening could not be made until yesterday.
"HBRC cannot mechanically dig a new river opening until the mouth is completely blocked by the gravel bank, and there is sufficient water in the lagoon to scour the new opening in the gravel as it is dug," said a HBRC spokesman.
"The swell conditions overnight closed the mouth fully, and the rain resulted in increased flows in the Ngaruroro and Tutaekuri rivers."
The spokesman confirmed the flood protection system was working as designed. Although the water was over the river sides, as frequently happens when the mouth was closed, it was contained within the stopbanks.
NZ Transport Agency central region spokesman Anthony Frith said State Highway 2 had been closed in Clive due to flooding from overflowing storm water drains. The flooding on the Napier side of the bridge was pumped out by the fire service.
"The highway was closed at the fire service's request. The flooding wasn't so bad on the bridge but the properties around it," he said.
He also said SH50, about 10km south of Maraekakaho, had been blocked by a slip at 6am, closing both lanes until mid-morning.
MetService meteorologist Daniel Corbett said parts of Hawke's Bay had received more than 150mm of rain, while Hastings had 50.2mm and Napier 28mm in a 24-hour period. In the same period, Park's Peak in the Ruahine Ranges was drenched with 156mm.
"We've certainly had quite a bit of rain. The really heavy downpours have occurred in the west of Hawke's Bay but the coastal areas have received a fair amount as well."
He said by this morning the low will have moved over most of the North Island, bringing a band of rain.
"Rain will be coming and going for 6-8 hours but in Hawke's Bay it will just be showery, and over most of the East Coast it will just be patches of rain here and there.
"Friday is washing on the line day. There will be a nice northwesterly flow, sunshine and a high of 21C."
He said it would stay mild over the weekend, with a westerly flow.