Agenda - Public Works Committee - 10/19/1999

Home

MEMORANDUM DATE: TO: FROM: RE: October 15, 1999 Dean Kapler, Director of Public Works Bill Goodrich, City Attorney Steven J. Jankowski, City Engineer Proposed Grading Plan Revision Lots 1, 2, 3, 8, 9, 10, Block 1, Apple Ridge I have reviewed three plan sheets submitted at the October 7, 1999 meeting with Orrin Thompson Homes, relative to the above referenced lots. The submittals included one plan sheet illustrating existing homes, lot lines, predevelopment two-foot contours, and existing grade spot elevations. The plan sheet identified six cross sections A-B, C-D, E-F, G-H, I-J, and K-L, illustrating a proposed drainage swale. Profiles of those cross sections are illustrated on the remaining two plan sheets. The plan sheet contains the existing lowest grade or walkout elevation of the residences within Block 1. The plan sheet also contains bold elevations along the property lines. These elevations are consistent with the front yard elevation of the approved grading plan. However, only the common rear yard boundary of Lots 5, 6, and 7 is consistent with the original grading plan. All the remaining bold rear yard elevations are presumably the proposed regrading plan. (This assumption woUld require the regrading of Lot 8, which was not consistent with my understanding of the lots to be involved from the verbal presentation at the meeting.) Observations: I have concerns with the submitted plan in the following areas: 1. t '.k As stated earlier, I am not sure whether Lot 8 is to be included in the regrading plan. If the bold elevation of the southernmost comer of Lot 8 is proposed to be 885.2, the existing grade is one foot lower only 20 feet away. The grade of the swale is flatter than 1%, between G-H and C-D. There seems to be an implied assumption that once the run-off reaches the northerly plat boundary, it is safely disposed. There is no analysis of how much capacity is available within the depression, nor is there a calculation of how much area drains to this depression. Based on a site visit, I do not feel it is a safe assumption that the area west of the depression continues the slope westward. This may be a landlocked basin. This plan should contain an analysis of a 100-year flood event. The cross section side slopes on the drainage pathway vary from slightly over 2% to an excess of 20%. I would consider the drainage way to be a swale in the locations where the slope is less than 10%, and a "ditch" at steeper grades. I have a concern that since the swale/ditch runs north/south and the prevailing winds are from west to east, there will be a tendency for the drainage way to fill with snow and ice in the spring of the year when critical melt/precipitation events will occur.