Greater South Haven Storm Water Improvements

Greater South Haven – Storm Water Infrastructure Study (UPDATED 9/26/2023)

The Porter County Department of Development and Storm Water Management (PCDDSWM) has undertaken a study of the stormwater infrastructure within the Coventry, New South Haven and Salt Creek Valley Commons subdivisions. Coventry, New South Haven and Salt Creek Valley Commons were constructed in the 1960’s through the early 1990’s and the age of the infrastructure is approaching 50 to 60 years. The primary pipe material of construction in New South Haven and Salt Creek Valley Commons subdivisions is galvanized corrugated metal pipe (CMP) and has a life expectancy of approximately 50 years (depending on specific site conditions). The majority of the pipes in the Coventry subdivision is high density polyethylene (HDPE). The areas have reported drainage issues, infrastructure failures (e.g. sinkholes) and were identified in 2010 County-wide Comprehensive Drainage Plan as areas of concern.

The study included video inspection of approximately 100,500 feet of storm sewer (approximately 19 miles) to assess the condition of the pipes. The video inspection confirmed the CMP pipe had visible corrosion and even areas of exposed soil. Standing water and sediment depth prevented video inspection in some instances. One pipe was almost completely corroded and was forming a sinkhole. The video inspection confirmed the majority of the CMP pipe was nearing the end of its service life.

The HDPE pipe in the Coventry subdivision displayed significant deformities, some so extreme the pipe was fractured. Inconsistent slopes were also frequently observed.

Hydrologic and hydraulic computer modeling was performed using the XPSWMM software to assess the potential flow capacity. Assuming the pipes were clean and in good shape geometrically, various storm events were run. The results found most of the pipes in all three subdivisions could convey the 10% annual exceedance probability (AEP) storm event (“the 10-year event) with the hydraulic gradeline (HGL) below the casting. The model was re-run with slightly reduced pipe diameters to account for possible lining. The most modified pipes continued to convey the 10% AEP event with the HGL below the casting validating possible lining activities.

Using both the video inspection and modeling results, multiple rehabilitation construction projects and costs were estimated within each subdivision for segments of the storm sewers to manage the overall budgeting. The following tables summarize the opinion of probable construction costs for each subdivision.

Greater South Haven Storm Water Infrastructure Study

Appendix I - Project Area Map

Appendix II - XPSWMM Model Input References

Appendix II A - Rainfall Depths

Appendix II B - Rainfall Distributions

Appendix III - Coventry Subdivision

Appendix III A - Coventry Subdivision Existing Conditions Map

Appendix III B - Select Video Inspection Photographs

Appendix III C - XPSWMM Pipe HGL Profiles

Appendix III D - Proposed Project Areas Map

Appendix III E - Project Opinions of Probable Cost

Appendix IV - New South Haven Subdivision