Existing Stormwater Programs
Most stormwater drainage systems are designed to capture and convey water away from people and property rather than for beneficial use. As stormwater flows across the ground, it picks up contaminants such as fertilizers, pesticides, dirt, and motor oil. Since stormwater can be a source of surface water and groundwater contamination, cities must comply with total maximum daily load (TMDL) implementation plans and applicable National Pollutant Discharge Elimination System (NPDES) requirements. To comply with state and federal requirements, cities typically develop Stormwater Management Programs to help protect rivers, both water supplies and valuable habitat areas.
For example, the City of Lodi published a Stormwater Development Standards Plan in 2008 to assist in the overall management and infrastructure planning for handling of stormwater runoff. The plan, which supplements the City’s Stormwater Management Program from 2003, includes Best Management Practices (BMPs) in six program areas: public education and outreach, illicit discharge detection, public participation/involvement, construction site runoff control, post-construction runoff control, and pollution prevention (B&V 2003). The City has teamed with the local community under its Storm Drain Detectives program. A group of teachers, students, and community members, in partnership with the City of Lodi, monitor the effects of storm drain runoff that flows from streets and drains into Lodi Lake and the Mokelumne River. The City discharges some of its stormwater into the Mokelumne River and the WID Canal, and retains the rest of the stormwater in DeBenedetti Park and Pixley Park detention basins. The stormwater flow directed to the detention ponds is allowed to dissipate by evaporation and percolation (City of Lodi 2008). Because some of the water is allowed to percolate, there are groundwater recharge benefits which may be realized. As such, utilizing a portion of this water could decrease the amount of recharge that is currently occurring.
Similarly, the City of Stockton operates five detention basins that were initially designed for flood control and three additional detention basins maintained for water quality and flood control. The City, along with the urbanized areas of San Joaquin County, updated its Stormwater Management Plan in 2009 to comply with new federal regulations to eliminate or control the discharge of pollutants. The program includes volume reduction measures, which arose from the volume reduction requirement that specifies the use of low impact development (LID). The volume reduction measures are BMPs that can be used to direct, retain, reuse and/or infiltrate stormwater runoff (LWA 2009). These detention basins are
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Many cities are evaluating potential LID principles and techniques which can be used to design and construct sites that minimize soil compaction and imperviousness, preserve natural drainages, and result in improved water quality. For example, the City of Manteca has included LID recommendations in its 2013 Stormwater Management Plan. It anticipates LID principles will be required in all new development after updates to the statewide stormwater NPDES Phase II permit.
In the MAC Region, the City of Ione has an inadequate storm drainage system. According to the 2009 City of Ione General Plan, in older section of the City, there are limited or no storm drainage facilities, requiring the City to place temporary storm drainage structure to contain runoff. The City intends to correct these deficiencies. This could provide an opportunity for the implementation of LID measures or local, small-scale stormwater runoff capture and reuse.
Based on research of existing documents, there are currently no existing or planned stormwater capture, treatment and reuse programs occurring in the MokeWISE region. Potential Programs
Stormwater could potentially be captured through large-scale capture and treatment projects and/or small-scale onsite capture programs (such as rain barrels).
Small-scale programs could include utilizing low impact development (LID) principles and implementing onsite systems such as rain barrels and cisterns. LID could be used to recharge upper aquifers, but its primary benefit is in reducing peak attenuations of storm flows and improving runoff quality. Onsite rain barrels at the residential level could be widely implemented if incentives were offered to property owners.
Groundwater storage and/or recharge are potential uses of collected municipal stormwater within the lower watershed. Stormwater could be banked within the groundwater basin during the wet months and extracted during the dry months. Partnerships between local entities could help facilitate localized transfers between banked groundwater and surface water. In addition to the recharge infrastructure required, storage and conveyance infrastructure would be necessary to deliver the collected stormwater to any recharge sites. The upper watershed is more rural residential in nature. As such, it is anticipated that onsite rainwater capture and use by individual residences would be the primary mechanism for rainwater capture and reuse in the upper watershed.
Captured rainwater can be used for outdoor irrigation and some indoor nonpotable uses. Indoor use of rainwater is typically regulated by the local health department, and allowable
uses vary, with approvals often occurring on a case-by-case basis. In California, rainwater has been used for indoor purposes such as toilet flushing and clothes washers. According to a 2011 study, the average single family home in northern California uses 295 gallons per household per day (gphd) (Aquacraft 2011, 128). Roughly 42% (125 gallons) of this total is for outdoor uses and 58% (171 gallons) is for indoor uses. Typically, approximately 20% of indoor use is for toilet flushing and 18% of indoor use is for clothes washing (Aquacraft 2011, 134). Assuming that a non-potable supply, such as rainwater, could be used for outdoor irrigation, toilet flushing, and clothes washing, the average single family northern California home could offset 190 gallons of potable water per day with rainwater if sufficient supplies and storage were available. Over the course of a year, this equates to approximately 69,350 gallons (0.2 AF).
As described previously, a typical residential parcel in the Jackson area is estimated to be 0.8 acres. It was assumed that approximately 10% of this area would be roof space; this corresponds to 0.082 acres, or 3,570 square feet. Assuming approximately 2.39 feet of precipitation falls in the upper watershed in an average year, and accounting for 50 percent losses, approximately 31,910 gallons (0.10 AF) of rainwater could be captured from a 3,570 square foot rooftop over the course of a year. This equates to 46 percent of estimated annual demand for non-potable supplies. This is a conservative estimate, as rooftop capture could have losses less than 50 percent. If rooftop systems were constructed on residential homes, water capture would likely be higher and annual water savings could be greater. The wettest month is January, when irrigation needs are at their lowest. Of the 31.910 gallons of water available for capture over the course of the year, 19%, or 6,060 gallons (0.02 AF), falls in January. Assuming storage capacity would need to be sufficient to capture the quantity of rainfall experienced in January alone, a 6,060 gallon cistern would be required (Figure 11). Depending upon the desired configuration, this level of storage could be achieved with an above-ground cistern that is 28 feet in diameter and 10 feet in height.
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Figure 11: Approximate Dimensions of Required Storage