Web Exclusive: Storm Sewer System Study
As part of an Indefinite Delivery Type (IDT) contract with the Corps of Engineers (COE) of the St. Paul District, Minn., M.J. Harden Associates Inc. (MJH), Kansas City, Mo., completed a photogrammetric mapping project providing aerial photography, ground control, topographic mapping, cross sections with soundings, and profile and utility surveys in late 1999. The mapping was to be used for the Montevideo Storm Sewer System Study and flood control. The purpose of the study was to determine how to best manage runoff from heavy rainfalls and prevent flooding. The results gave the city an accurate picture of the structures that were currently in place and help the city to determine whether they needed additional inlets and/or resizing of the sewers.
MJH enlisted the services of a professional engineering and land surveying firm to provide additional survey capacity for the 755-acre project area in Montevideo, Minn., in the Minnesota River Basin, approximately 135 miles west of St. Paul.
Furnished with copies of the existing Montevideo storm sewer maps, the surveyors tried to locate the manholes and inlets. There were several discrepancies and the crews had to verify most of the structures along the river and obtain inverse depths and pipe sizes. It was difficult tracking the storm sewer lines back from their outlets, and in the process, the crew uncovered several manholes that the city was not aware of or possessed records of. The crew started back at a storm sewer inlet and have the city flood it with water. Then, they would work out a block at a time and use what information they had to track the flows from manholes found until they tracked it all the way to its outlet. In one case, they found water bubbling out of the ground. This is when they discovered an outlet to the storm sewer that was completely buried. By going through this process, the crew was able to update the city’s maps with correct information.
Field survey planning and preparation included researching NGS and USGS for horizontal and vertical control documentation and obtaining original copies of USGS 7.5 minute topographic maps. Right-of-entry permission was obtained from landowners on the properties affected.
Surveying included two cross-sections on the Chippewa River extending 100' beyond the top of the normal channel bank and elevations of a 25' interval on land. Soundings in the channel were obtained at 10' intervals. A temporary benchmark was set at each cross section location.
Flown 3000' above mean terrain with a photo scale of 1:6000, the crew obtained aerial photography using a Jena LMK camera (Jena, Germany) with a 153 mm focal length and forward motion compensation (FMC). Each aerial photo frame was scanned direct from the aerial film on an Intergraph PhotoScan TD1 (Intergraph, Huntsville, Ala.). This provided the St. Paul COE with overlapping scanned images, which can be viewed in stereo. The digital images were also analytically bridged (or connected together) with an Intergraph program called Match-AT, which provides a stereoplotter operator with machine set-up readings and gives an overall adjusted geometric solution for the project.
The stereo models were set on the ImageStation Z stereoplotters where the compiler collects the plan detail that can be identified. Features such as roads, utility poles, buildings, fence and tree lines, water surface and shoreline were included. The compiler also collects breaklines, formlines and random spots (DTM data), which is used to generate a triangle file and subsequently, final contours.
Using Trimble 4000 SSE receivers (Trimble Navigation Ltd., Sunnyvale, Calif.), GPS RTK (real-time kinematics) established Minnesota State Plane coordinates, NAD83, South Zone and NAVD29 elevations on 14 photo identifiable points. Using GPS RTK to obtain x, y, z coordinates on the east set of railroad tracks (highest rail), railroad profile surveys were obtained for approximately 4,700', establishing three temporary benchmarks.
MJH provided the field survey data, final mylar drawings and one CD-ROM that contained all the digital data. The project was completed in 110 calendar days, two days earlier than required. Total project cost of $33,933 was within budget.