Geotechnical Design and Construction of Gabion Shoreline Protection for an Integrated Creek Improvement Project in Diobu Creek, Port Harcourt, Niger Delta, Nigeria

Urban waterways in the Niger Delta are increasingly exposed to channel siltation, bank erosion, uncontrolled waste deposition, hydraulic scour and progressive loss of channel capacity. These problems are particularly critical where shoreline stabilization must be undertaken concurrently with dredging, reclamation and navigation improvement on weak, saturated sediments. This study presents the geotechnical investigation, design and construction of a gabion-based shoreline protection system implemented as a component of the integrated improvement of Diobu Creek, Port Harcourt, Nigeria. The study combines topographic and bathymetric surveys, tidal observations, three geotechnical boreholes, particle-size analysis, permeability estimation and direct shear testing to establish the engineering conditions controlling shoreline stability and revetment performance. The investigated riverbed comprises approximately 1.2–1.6 m of very soft to soft organic silty clay underlain by predominantly medium-grained, relatively uniform sand extending to at least 12 m below the riverbed. The sand exhibits an estimated hydraulic conductivity of approximately (4.41 × 10 -3 ) m/s and an average angle of internal friction of about 34°. These conditions necessitated careful management of saturated sediments during excavation and construction below Low Low Water (LLW). The adopted protection system comprised shoreline sand filling and regrading, excavation of weak foundation sediments, placement of a 0.45 m crushed-stone foundation layer, installation of a high-strength geotextile filter/separator, placement and interconnection of zinc-coated gabion baskets filled with durable crushed rock, and construction of a crest/anchor beam. A 1V:2.5H bank slope was adopted to reduce the potential for instability while providing an appropriate geometry for the gabion revetment. Construction experience demonstrated that the principal geotechnical challenges were instability of saturated soft sediments, localized failure of the regraded sand slope, seepage and piping risks, toe scour, and the need to synchronize excavation and foundation placement with tidal conditions. The study demonstrates that gabion revetments, when integrated with appropriate foundation preparation, geotextile filtration, toe protection and drainage, can provide a flexible and permeable shoreline stabilization solution for urban tidal-creek environments. The findings provide a practical framework for the design and construction of shoreline protection systems in the soft, sediment-dominated environments of the Niger Delta.