Liberty County Master Drainage Plan Stormwater Solutions

Abstract

Liberty County is located northeast of Houston, TX. Three major communities lie within Liberty County, and they are: Liberty, Dayton, and Cleveland. The Trinity River also passes through the heart of the county. The majority of the land in Liberty County is wetlands, especially near the banks of the Trinity River, and so due to the land being below sea level, flooding is a big issue for the county and its residents. In recent years, Liberty County has had some serious issues with flooding due to intense and periodic storm events. With the expansion of the Houston area, and with the construction of the 99 Corridor, Liberty County is predicting a lot of growth in terms of population in the near future. With an increase in population comes an increase in more urbanized areas. These new urbanized areas will increase the peak flow of a precipitation event as well as the peak time. With this information and predicted growth, Liberty County is faced with the problem of creating a master drainage plan in order to prevent future precipitation events from creating worse flooding issues. For the purposes of our project, we were asked to design the master drainage plan for Liberty County. We are to create a design that utilizes Low Impact Development (LID) practices, and we are to account for the predicted growth of Liberty County by getting the projected runoff of a precipitation event back down to predevelopment levels. Our plan of action to address this problem is to create a drainage plan by utilizing the SCS Curve Number Method. By using the curve number method, we have created a hydrograph for a 10-yr, 12-hr storm, which is the storm that the county officials specifically preferred. We used GIS (geographic information systems) and SWAT (Soil and Water Assessment Tool) in order to delineate a watershed with multiple sub basin watersheds within the county. We focused on the smaller watersheds that the cities are primarily in, and the areas where the expected growth is to occur. We utilized GIS in order to calculate the area (acres), the length of the stream (ft), the slope (ft/ft), the soil, and the land use for each watershed that we are interested in. By knowing all of this pertinent information for each watershed, we were able to calculate the peak flow and peak time for each watershed for predevelopment. After calculating the peak flows and times, we then created different scenarios based on the predicted growth of Liberty County. With information provided by the Texas A&M Architecture group, we accounted for predicted growth by changing the land use curve number to values for higher development for each watershed. By changing the land use in each watershed, we achieved higher flow rates and earlier peak times as predicted. After achieving the new peak flows and peak times for future development, we began implementing the curve numbers for our recommended LID practices into our design. Three LID practices that we chose within our design are rain gardens, rainwater harvesting, and permeable pavement. By implementing these LID practices, we were able to reduce the new peak flows and peak times back down to acceptable levels, or in this case predevelopment levels. Overall, our design solution was a success in reducing the peak flow, peak time, and the total flow of future conditions back down to predevelopment conditions. By creating hydrographs, we were able to visually see the difference in peak flow, peak time, and total flow that new urbanization would bring as compared to predevelopment levels. Our results prove that with urbanization, runoff will increase at alarming rates, and that with the implementation of the recommended LID practices, these runoff conditions would be reduced to acceptable levels.