2021 Kitsap County Stormwater Design Manual
2021 Kitsap County
Stormwater Design Manual

4.7.3 Level 3 Analysis

A Level 3 analysis shall be performed for those existing or predicted drainage problem locations where the director determines that the analysis results shall be as accurate as possible. Examples of conditions that might require a Level 3 analysis include:

  • If the site is flat and does not drain well;

  • If the system is affected by downstream controls;

  • If minor changes in the drainage system could flood roads, buildings or septic systems; or

  • If the proposed project will contribute more than 15% of the total peak flow to the drainage problem location.

The Level 3 analysis is similar to the Level 2 analysis but is a more precise quantitative analysis, utilizing field survey profile and cross-section topographic data prepared by a licensed professional land surveyor or engineer. The following steps shall be completed for this level of analysis:

  1. Develop solutions to drainage problems identified by the analysis. For any existing or predicted offsite drainage problem, the engineer shall demonstrate that the proposed plan has been designed so that it neither aggravates the existing problem nor creates a new problem. As an alternative, the applicant may arrange with the owners of the affected offsite properties to install measures, which will correct the existing or predicted problem, subject to all applicable permit requirements.

  2. Any proposed drainage easements shall be signed by the affected property owners and be recorded prior to approval of the proposed plan. In some cases, an existing drainage problem identified by the local government may be scheduled for solution. In these cases, the applicant should contact Kitsap County to check for potential cost sharing to solve the existing problem.

  3. For any predicted offsite problem, the engineer shall demonstrate that the proposed plan has been designed to mitigate the predicted problem. As an alternative, the applicant may arrange with the owners of offsite properties to install measures, which will mitigate the predicted problem. Any proposed drainage easements shall be signed by the affected property owners and be recorded prior to approval of the proposed plan.