провал

[Bigor]

need for comments

По мнению специалистов-гидрологов, такой сброс стоков может создавать угрозу размыва песчаной основы шоссе и образования провалов на полотне дороги

Such waste water discharge in opinion of hydrologists may cause threat of highway sandy basis washout and formation of roadbed failures

[operator]

According to hydrologists, such wastewater discharge may cause washout of the highway's sand base and create hollows in the roadbed.

IMHO

[Bigor]

great, especially to "hollows"

[alikan]

оно же - cavity

[Kot_Maks]

К варианту Operator'a
...and create hollows in the roadbed.
IMHO лучше изложить как
...and thus may result in hollows in the roadbed.