An injection molded plastic corrugated leaching or storm water chamber has
a peak corrugations segment with a flattened and thickened web. The web
is the portion of the corrugation which runs from the peak to the floor
of the adjacent valley. Preferably, flattened web segments are at the
apexes of adjoining corrugations, to create an increased thickness band
region, running lengthwise along the chamber from an injection nozzle
location or sprue. The flattened web segments enable better melted
plastic flow during molding, without increasing nesting height.