Heavy rains on Sunday resulted in drainage issues and flooding in three spots on Oahu highways, according to the Hawaii Department of Transportation, which is revising its protocols for future storms.

DOT admitted it was not expecting the heavy rains over Honolulu that resulted in flooding and seriously backed-up traffic on the H-1 highway, eastbound, near the Punahou off-ramp, as well as on H-1 westbound near the Liliha overpass, and westbound Nimitz Highway near Iwilei Road.

Going forward, DOT said it will prepare for heavy storms and flooding by performing checks on drains and bridges, rockslide areas, and low-lying spots along freeways, highways and roads.

>> At about 1:50 p.m. Sunday, flooding was reported on the H-1 eastbound near the Punahou off-ramp. Crews responded but did not reach the area until about 5 p.m. due to heavy traffic. They were able to clear the drains by 5:51 p.m. According to DOT, they were hampered in their efforts due to filtering fabric installed for a nearby repaving project and had to cut through it to drain water and clean gravel off the road.

>> At about 9 p.m. Sunday, flooding was reported on H-1 westbound near Liliha. Crews cleared the drains there by about 11:15 p.m. and then washed gravel and debris off the roadway by about 11:50 p.m.

>> At about 9 p.m. Sunday, flooding was also reported of flooding near Iwilei Road. Crews finished up at Liliha first, then headed to Nimitz and cleared the drain at about 12:50 a.m. Monday. Crews at 3 a.m. resorted to vacuuming two truckloads of water from the road because the water level remained high, blocking two lanes, despite the cleared drain. All water was cleared by about 4:50 a.m.

DOT said going forward, it will remove filtering fabric to better manage drainage from the Punahou area, when work is not underway, adding about $50,000 more to the project to be completed in about three months. Additionally, DOT will adjust the threshold for storm preparations and alert on-call crews to prepare known flooding areas for “any potential hydrological event.”

A flood advisory was in effect for Oahu through Sunday night due to heavy showers and thunderstorms, and upgraded at about 10 p.m. to a flash flood warning as rain fell at a rate of 2 to 3 inches and hour.