OCEAN OUTFALL REPAIR TECHNIQUE OFFERS REDUCED RISK AND ECOLOGICAL BENEFITS

摘要

The City of Hollywood is responsible for the Hollywood Southern Regional Wastewater Treatment Plant, which is rated at 42 million gallons per day and discharges secondary treated effluent to the Atlantic Ocean via a 60-inch ocean outfall. The outfall is currently the primary method of effluent disposal for the treatment plant. After the passage of Hurricane Andrew in 1992, the outfall required rehabilitation of its cover material over four discrete problem areas comprising a total of approximately 4,000 feet. An articulated concrete mat was chosen at that time to effect repair of the armor covering. Use of the concrete mats offered several advantages over the traditional armor rock, the most notable of which was a more stable cover material that was quicker to install. Adjoining mats were connected together with polyester cable, forming a contiguous repair. The rehabilitation was completed in late 1994. A subsequent inspection of the outfall was performed in May of 1997 to document the integrity of the cover material. At that time, no damage was found to either the original armor rock cover material or the rehabilitated cover material. Because Hurricane Irene, which passed through south Florida on October 15, 1999, caused an estimated $120 million in damage in Miami-Dade County alone, the City of Hollywood conducted another inspection of the outfall in March 2000. The results of the inspection found a substantial amount of the original cover material was missing and that the outfall was visibly exposed in various areas. No visible leaks were found and all exposed pipe appeared to be in good condition. All areas previously repaired with the articulated concrete mat appeared in good condition and exhibited substantial marine growth. Based upon the inspection results, the exposure was not deemed to be extensive and totaled about 82 feet in length. The single largest area in need of repair was approximately 24 feet in length and contained one exposed pipe joint. Options for the extent of repair/rehabilitation were developed and compared as a function of relative risk of continued cover material loss, cost and construction time. Selection of an alternative to implement depended upon available funding and judgment as to the value of the expense versus its corresponding reduced risk. The resistance of the previous repair to storm damage was highlighted.