**5. Design criteria considerations**

The design structure of a riparian buffer involves estimating the appropriate size, shape, and vegetation composition to address multiple objectives at a particular location. The location provides information concerning climate, stream characteristics, watershed water delivery, native vegetation inventory, and other factors [7]. Initial considerations must assess which resource issues are particularly important to the design process. Seven key resource considerations include: (i) water quality, (ii) biodiversity, (iii) fertile and productive soils, (iv) economic opportunities, (v) protection and safety, (vi) esthetics and visual appearance, and (vii) recreation potential. The landowner, in consultation with a professional soil engineer, must establish the problems and opportunities, then determine site-specific objectives. Within this context, a resource inventory is conducted and evaluated to complete the riparian buffer design [7].

In our case, we selected water quality as the most important resource consideration. Our objective was to reduce nitrate transport because of overland flow and shallow groundwater flux towards Williams Creek. Our defined buffer functions were: (i) slow water runoff by optimizing soil infiltration, (ii) trap nitrate from both overland and subsurface flow because of enhanced infiltration and plant uptake, and (iii) reduce soil surface and bank erosion. In this project, published design guidelines selected for water quality are partitioned as: (i) location and arrangement, (ii) size and pollutant type (nitrate), (iii) native vegetation, (iv) management, and (v) incorporation of additional guidelines that may benefit water quality [7].

For water quality, the category of size and pollutant type contains the following guidelines germane to reducing nitrate pollution: (i) variable buffer width correlation with runoff volume, (ii) effective buffer area ratio by considering upslope runoff area to the riparian area, (iii) slope and soil type adjustments, (iv) buffer sediment capturing requirements based on sediment particle size distribution, (v) nitrogen soil capture because of leaching, and (vi) presence of shallow groundwater. Criteria for the seven resource issues are expertly detailed [7].
