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SECTION 2 Study Area Characteristics 2.5.4 Drywell Drainage System Drywells are underground structures that collect stormwater runoff which is then discharged into the ground where it mixes with the groundwater. The River Road Santa Clara stormwater basin is unique compared to other Eugene -area basins in its frequent use of drywells for managing stormwater. Approximately 22% of the River Road Santa Clara stormwater basin currently drains to drywells. This area has historically utilized drywells because it lacks a continuous stormwater system and because the flatness of the topography and the relatively high permeability of the soils are conducive to stormwater management through this method. There are 785 known drywells in the River Road Santa Clara basin. Of those drywells, 634 (81 %) are privately owned, 79 (10 %) are owned by Lane County, and 72 (9 %) are owned by the City of Eugene. Drywells come in numerous configurations which are collectively termed "Underground Injection Controls" or "UICs." 2.5.5 Maintaining the Drainage System The Lane County Public Works Department, the Junction City Water Control District, and the City of Eugene share limited maintenance responsibilities in this basin. Lane County Public Works Department is responsible for stormwater facility maintenance in the unincorporated portions of this basin. This maintenance activity is limited to drainage problems that directly affect County right -of -way, such as roadside ditches, culverts, and bridge crossings. The Junction City Water Control District is responsible for maintenance of irrigation ditches, channels and waterways within the District's boundaries, which lie in the unincorporated areas north of Eugene in the Flat Creek, A, A -1 and A -2 Channel watershed boundaries. The City is responsible for maintaining areas that have been annexed to the City. The City and County share maintenance responsibilities in this basin which results in greater efficiencies for both jurisdictions. 2.5.6 Floodplain A flood insurance study for the Federal Emergency Management Agency (FEMA) has been conducted within the River Road Santa Clara basin. As part of this study, areas subject to the 100 -year flood event have been identified. One thousand two hundred seventy acres of floodplain have been mapped within the basin. There are approximately equal acres of floodplain within and outside the UGB. Most of the broad floodplain area is associated with the Willamette River in the northeast portion of the basin just outside the UGB. Ribbons of floodplain are also located adjacent to the five primary waterways that flow through the basin. (See Map 5) More detailed floodplain studies necessary to map floodway boundaries have not been conducted for this basin. 2.6 Water Quality This section provides a description of water quality conditions in the River Road Santa Clara basin. Water quality conditions can vary dramatically depending on time of day, weather conditions, land use activities conducted in the watershed, and location in the water body. Therefore, without significant amounts of data, it is often difficult to adequately evaluate water N:ASTORMWATER \City of EugencARR_SC Stormwater Basin Plan\2012 Document \Master_ Plan _9- 18- 12_DR-AFT Word Version.doc 2 -17