Details of secret midnight rituals conducted over countless generations at the Phiphidi waterfall near Thohoyandou have emerged as the clan that protects the site fights to save it from destruction.

The Ramunangi clan, led by Tshavhungwe Nemarude, who says she is about 84, is seeking an urgent interdict to block Chief Jerry Tshivhase, the Tshivhase Traditional Council and a development trust from continuing work on tourist chalets and related facilities at the site.

In affidavits filed in support of their application for a court order, the clan accuses the traditional leaders of violating legal requirements and ignoring the clan's "duty" to maintain the spiritual wellbeing of the Venda people.

"All of our rituals involve communicating with and appeasing the ancestral spirits that guide and protect our people," said Nemarude, who describes herself as the senior female leader or makhadzi of the clan.

But in a letter to the clan's lawyer written in April, an attorney representing the respondents, Anton Ramaano, wrote: "Our client sends a strong warning to your client that before he could approach the court of law he would have thought twice."

The dispute has been simmering since June 2008 when the Ramunangi clan heard rumours of the planned tourism development.  They asked Limpopo provincial government officials to intervene, but were told that the project was the responsibility of Chief Tshivhase.

After clan representatives approached the chief, councillors at the Venda royal palace told them they had no rights over the land because it belonged to the Tshivhase tribe.

In April, earth-moving equipment began clearing the site, and work started on chalets and rondavels. In her affidavit, Nemarude said the clan had never claimed ownership of the land, but wanted to assert its "ancient and informal rights to protect the sacred site".

She said clan elders had never shared their knowledge of the sacred rituals, but were willing to reveal some of the secrets now as part of their efforts to save the Phiphidi waterfall from desecration.

She said one of the main rituals, thevhula, which was "carried out in complete darkness", was an essential part of prayers to the ancestors to send rain, preserve the health of people and crops, and ensure that peace prevailed.

Henk Smith, a lawyer with the Legal Resources Centre who is helping the clan, said they were brave to proceed with their action in the face of the warning from Ramaano. "The bigger context has got to do with these powers that the chiefs abrogate," he said. "They don't like it that this clan says that it's got rights."

Belgian anthropologist Jean Dederen, who has studied Venda culture for more than 30 years, said the existence of the Phiphidi sacred site had been reported by missionaries in the 19th century.

"Many of the sacred sites in Venda are believed to be linked," he said.

"Damage to or neglect of one site is believed to affect the other sites and their overall spiritual essence. War, disease, starvation and any other serious social calamity on a national scale is explained in terms of desecration of sacred sites."