Microbially-Induced Calcium Carbonate Precipitation (MICP) Supporting Nearshore Dellanera Reef Design for Galveston Island
MICP is an integral part of a process that allows naturally occurring microbes to bind sediment grains together. The increase of cemented bonds between individual grains leads to a more stable sediment matrix. Depending on the level of cementation, MICP treated sediment displays increased resistance to erosion.
The intent of this project is to include natural and nature-based features (NNBF) and engineering with nature principles to effectively and sustainably deliver economic, environmental and social benefits to a submerged reef project offshore of Galveston Island, Texas. Investigating the implications of using MICP processes to aid in the creation of submerged reefs that can help mitigate shoreline erosion and is the focus of this CEL research. The three main research objectives are:
- the determination of the optimal conditions and parameters to achieve maximum efficiency in the MICP process using sand from the project location;
- the assessment of best practices for use of MICP enhanced sand in coastal erosion and flood risk reduction measures such as submerged reef design and construction;
- the collection and analysis of select hydrodynamic and sediment data at the field site to supplement the design process.
Objective 1 is accomplished through laboratory testing of various strategies to induce MICP processes. Aside from adding calcium chloride (CaCl2) solution to the sand, this includes comparing the traditionally used S. pasteurii (formerly known as Bacillus pasterurii) over naturally occurring microbial communities at the project site and determining the significance of urease activity on MICP. Both aerobic and anaerobic conditions are tested as well as the addition of glucose to enhance the MICP process. In addition, different sources of organic carbon (glucose vs fructose), growth media (marine broth vs yeast extract), pH (5, 6, 7 and 9), and lastly impact of additional supply of carbonate ions (in the form of sodium bicarbonate) are assessed. Physical, biological, and chemical parameters of the MICP enhanced sand are measured and analyzed to identify the optimal configuration.
Objective 2 is accomplished via testing the optimal MICP configuration in the field. In-situ use of MICP to stabilize sand on the beach near the Dellanera RV park on Galveston Island is investigated. Both open surface and geofabric enclosed MICP options are tested to assess construction and design practices for MICP submerged reefs. Further laboratory testing on the stability of rock slopes with and without the addition of MICP enhanced sand is carried out to address the potential use of MICP to improve common coastal revetment structure performance.
Objective 3 is accomplished through the deployment of an acoustic Doppler velocimeter (ADV) and a pressure transducer (PT) in the surf zone near the project site over a period of several days capturing calm and stormy conditions. In addition, several grab samples of the surface sand near the project site are collected and analyzed for sediment characteristics including grain size distribution.