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plans supplied by the Minnesota Department of Transportation, these sub-watersheds were measured and evaluated to enable storm-event modeling. In addition to the direct overland runoff that the lake receives, Twin Lake may receive stormwater flow from three culverts. To the northwest, a system of two culverts (a 36-inch diameter concrete pipe, followed by a 24-inch concrete pipe} carries water from the low park land associated with the trailer park. The triangular basin of land southwest of the railroad tracks drains to the lake via a 48-inch concrete pipe. Overflow from Vadnais Lake may also occur through an arched corrugated metal culvert _ under Twin. Lake Beu?evard. Culvert conditions, sizes, positions, and inlet and outlet invert elevations were identified. The drainage system is shown in plan view on Flgure 2, and in profile on Figure 4. Owing to its low elevation, mild slope and large diameter, the culvert under the railroad tracks may also act as a flood outlet for Twin Lake when water levels become extremely high. Water would flow from the Iake to the basin north of Interstate 694, and from there through the culvert under I-694 and into County Ditch 16. It must be noted that there are two problems associated with this outlet for Twin Lake: 4 The land surface in the basin southeast of the railroad tracks rises in front of the entrance to the culvert running below the westbound leg of Interstate 694, effectively creating a dike restricting flow to the pipe under the freeway. The invert elevation for the I-694 culvert is given by Mn/DOT as 872.3 feet. However, the terrain presently dictates that flow to this conveyance cannot occur until the water level in the basin exceeds the height of the low point in the °dike°, at 876.9 feet. o The culverts under the Interstate highway are of relatively small diameter and very little slope. The first of the two culverts is 30 inches in diameter; this. connects to a 36-inch culvert that passes under the eastbound leg of the freeway. Mn/DOT maps show the slope of the culvert system to be only about 0.03 percent. At the lake's flood elevation of 875 feet, this system is incapable of transmitting more than 14 cfs, much less than the projected 63 cfs. 23\62\264\TWINLAI~.~ 6