March 26, 2008
Storm Water Solutions
Texas State University
San Marcos, TX 78666
Bob Stafford
GIS Specialist/Cartographer, Facilities Planning, Design and Construction
Texas State University
San Marcos, TX 78666
Dear Mr. Stafford,
This letter will inform you of the progress Storm Water Solutions has made so far in our analysis of storm water runoff and proposed detention pond locations on the Texas State University campus. This letter includes a brief overview of the purpose and scope of our project, work completed, work in progress, and future work. We began work on this project after our submitted and approved proposal on February 20, 2008 and will complete our study by May 5, 2008. Our project is coming along as scheduled and on budget as submitted in our proposal.
Purpose
The San Marcos River is one of the most pristine and ecologically sensitive rivers in Texas. The river is not only aesthetically pleasing but it is also used for recreation such as swimming, snorkeling, diving, canoeing, kayaking and fishing. Texas State University is located on and just uphill of the San Marcos River, therefore, when it rains much of the storm water runoff from campus ends up directly in the river.
Storm water runoff, especially from impervious surfaces, when left untreated contains many pollutants and can reduce the water quality of any given water shed. Detention ponds are one of the most effective Best Management Practices (BMP) for controlling and cleaning storm water before it reaches our rivers.
Texas State’s current storm water drainage system is out of date and has not kept up with the construction that has occurred over the past several years. There are some storm water controlling devices, but they do not capture a majority of storm water from impervious surfaces. The goal of our research is to identify areas where storm water runoff, especially from impervious surfaces, can be collected and filtered in a detention pond before entering the San Marcos River. We will also look at future construction to ensure that these locations can accommodate future runoff from new buildings and parking structures.
Scope
Storm Water Solutions will only look at the drainage areas on Texas State University’s main campus and will keep our analysis within property lines. We will focus solely on the campus drainage system. Analysis of the city of San Marcos’ drainage system on parts of campus will not be included because it is too broad and will require more time than this project can offer.
Our team will only locate the potential sites for detention ponds using GIS tools and will not be involved in the actual construction of the ponds. Although we do know how these ponds operate and perform, we will not consult others in the engineering of these ponds.
Work Completed
As of March 26, 2008, Storm Water Solutions has compiled all the data that is needed to begin our analysis of potential storm water detention pond locations. The collection of primary and secondary data went smoothly and enables us to move forward with confidence and ahead of schedule in our analysis. The following is a breakdown of the work that has been completed by Storm Water Solutions thus far.
Collection of Primary Data
Our team performed a complete walkthrough of Texas State University in order to get a general feel for the terrain, slope, and layout of campus; this gave us a better idea of how water would flow on campus during a rain event. We identified several areas on campus that have great potential for detention ponds. These locations were determined after observing available and undeveloped land in respect to the storm water drain network. Our team took multiple photos of these areas and plotted the locations of major storm drain outlets and problem drain areas via GPS. Our visual analysis of campus enabled our team to formulate new approaches in thinking in respect to how, where, and why we are going to go about in placing storm water detention ponds.
Organizing Secondary Data
The initial shape file data that was provided to us by the university is an invaluable resource and it allows us to complete this project on time. To begin with, we were given a bulk set of data; in order for our team to effectively use this data we had to organize it and sift through it to decide what we were going to use and what we needed. Organization techniques included merging proper shape files to eliminate data frame crowding, as well as adding attribute table fields and data to further enhance our SQL operations. Clipping and joining files has also been done in order to obtain datasets that are pertinent to our study.
Our team has made accurate measurements of all the impervious surfaces within the Texas State University boundary. We have also analyzed the green zones and the soil conditions that exist within the boundary. Green zone analysis was performed using remote sensing measurement techniques, and our team utilized extensive fieldwork to formulate the specific percentage of poor soil conditions that exist in each green zone.
All of the actions completed so far are vital to our current and future work because we will build on them to formulate our runoff and watershed analysis.
Models Made
Our team created a Triangular Irregular Network (TIN) and a Digital Elevation Model (DEM) of the Texas State University campus from 2ft topographic lines provided on the W drive. The creation of these models will enable us to perform flow accumulation, flow direction, catchments, and other ArcHydro operations that are necessary for watershed analysis.
Current Work
This section contains information on work in progress as of today.
Watershed Analysis
We are currently working to define the watershed drainage zones. This is to facilitate a better understanding of the project area and allows the campus to be subdivided into manageable drainage zones. These smaller zones enable a more accurate estimation of how and where each subdivision drains and in what direction the general flow is. These accumulation areas will further reveal the details of the surface flow of water during a storm event and help in specific defining of the initial areas where a detention pond should be located.
Rainfall Projection
We previously discussed during our first meeting that the first two inches of rainfall is a very important variable, as it is utilized in calculating how large the ponds will be. Since the first two inches of rainfall wash nearly all of the contaminants off of the impervious surfaces it is the most necessary to contain, and the very reason to have a detention pond. With this in mind, the total square footage of each impervious cover polygon we have calculated is currently being added as a new field to the attribute table (if one had not existed before). This will allow our team to calculate each building, sidewalk, street and parking area’s individual contribution to the total amount of rainfall. The added benefit is to also have this data georeferenced to allow it to be used in future analysis. By multiplying the square footages with a third dimension of two inches of rainfall depth, we will be able to calculate how much water and thus how large the size of the ponds will be at any location we see fit.
Soil Runoff
As part of our project and outlined in the proposal we are adding soil-runoff estimation for all of the green spaces on campus. Our team believes that calculating the amounts of sediment that will be added to the runoff load before, during, and after future construction projects is a very important factor to consider in this analysis of detention pond location. In order to do this, we are using the Revised Universal Soil Loss Equation, RUSLE. The RUSLE equation is a well respected algorithm that is utilized either directly or indirectly by the Bureau of Land Management (BLM) and the United States Department of Agriculture (USDA), among others, to estimate soil loss in many environments. It has six factors it takes into consideration before giving up a total soil loss in tons per acre per year. Right now the six factor layers are being gathered and converted into the necessary units to allow the intersection of all the layers into one master polygon shapefile that has all the factors in its attribute table. With this done the final calculation of total soil loss can be performed. These factor layers include:
- Length/Slope or LS factor
- Ground Coverage layer or C factor
- Erosivity of soil factor or K
- Rainfall averages or R factor
- Management Practices or P factor
Once assembled, the influence of future developments can be added to the coverage factor then re-intersected and multiplied as before to produce a new estimate.
Future Work
Master Plan Integration
Our group will have to take into account the future construction that will take place on campus. We will have to synchronize our project with the ten year Master Plan so the storm water detention ponds will not be placed in an area that has already been designated by the university. The ponds also need to be placed in a large enough area that can accommodate runoff from future impervious surfaces.Storm Water Solutions will use the Master Plan as a guideline to survey land that will serve as prospective pond sites and still be available when all the construction is completed.
Drainage System
The current drainage system will need to be analyzed in order to get an accurate assessment of how much water flows through the system and where it goes. This data will not only help us locate good quality areas for the detention ponds but will also help us decide if new pipes need to be laid to divert the flow to a pond or another location.
Final Pond Location
The final step of the project is to locate positions for the storm water detention ponds with all factors weighed in. Using all of our analyses and the ten year Master Plan, we are confident we will find suitable locations for the ponds.
Conclusion
Storm Water Solutions has done extensive literature review and research on detention ponds and knows how these ponds work to reduce pollution. We realize that strategically placed ponds can greatly benefit the university and the local community in a tremendous way. The ponds will not only help the local environment by improving the water quality of the San Marcos River, but will also give Texas State credence as obtaining responsible, pollution-free development in relation to water quality.
With the collection of primary data, filtered and organized secondary data, and base models made, we are well on our way to completing the analysis portion of the Texas State University Campus Storm Water Project and should have potential sites plotted within a few weeks. We have encountered no major problems that were not easy to overcome thus far, and we do not foresee any other obstacles that would hinder our progress at this time.
If you have any questions, comments, or suggestions for our team, please feel free to contacts us by e-mail. Thank you for your time and support.
Sincerely,
Storm Water Solutions