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Impact on Drainage

BASIN	Total Parcels in High Category	TOTAL CAPTURE (Gal)
NPDES 012	43	1625167.8
NPDES 013	231	3947647.14
NPDES 014	34	591818.48
NPDES 015	181	2685912.59
Total	489	8850546.01
Table 2: For each priority basin the summary of total parcels and gallons removed from drainage system.

Drainage has become an important consideration of urban regions. Plagued by damage to regional the economy, public health, and ecology municipalities are anxious to address citizen concerns. To begin addressing some of these issues, we estimated the amount of water removed from the drainage system in the four priority basins. This procedure estimates total reduction of flow into the combined sewage overflow system from installation of rainwater harvesting systems on parcels deemed with high conservation potential. Within the high category parcels, we found that a total of 8.85 million gallons (33.50 million liters) can be captured by installation of rainwater harvesting systems. As a result, the equivalent amount can be removed from the drainage system. While we recognize that all rainfall cannot be captured in these basins, these figures represent total potential, and should be regarded as such. Table 2 summarizes the calculation from each of the four priority basins with total parcel number and gallons of rainwater capture.

Discussion
The GIS analysis used in this study was essential to evaluate systematically the potential for installing rainwater-harvesting systems within the city of Seattle. The ability to overlay large varied datasets, and code for specific representations proved easy and effective. In fact, due to readily available geocoded data for the city of Seattle, we were able to complete this portion of the project in a timely and efficient manner. Through this analysis the City is able to prioritize parcels that could potentially be candidates for installation of such systems. Clearly, some of our assumptions will need to be examined in greater detail when installation of a system is to occur. For example, we are comfortable with the assumptions of homogenous land cover, equal irrigation rates and total rainfall capture at the basin scale; however, at this point it is impossible to know if the specific parcel of interest is able to accommodate the installation of a rainwater harvesting system. There are many instances where landscaping or configuration of underground piping/wiring may prevent such installation. Therefore, we recommend ground-truthing all parcels of interest and evaluating the area for any circumstances not captured in this analysis. With the success of applying this methodology to the four priority basins we expect to perform this analysis to the entire city of Seattle in the near future. As such, we expect to identify all regions with high conservation potential and use the GIS to present the findings to city officials. With limited resources to spend on innovative project at the city scale, this methodology enables us to identify specific parcels where investments can occur. The next phase of this study will examine the fiscal implications of installing these systems on selected parcels, and the willingness-to-pay of those households selected.

Conclusion
Water demand indicates both current and/or expected water consumption in any given area over a specific time period. Due to varying requirements and spatially explicit characteristics of individual users, water demand must be determined separately for individual user groups. Multiple uses of water can be differentiated according to the demand for potable water, industrial/commercial processes, as well as irrigation. The advantage of using a GIS for this analysis is that it helps with the initial identification of the parcels, visual cross checking with statistical data, and provides a platform for presenting the analysis to city officials for review. We hope that the study presented here establishes a basis upon which future research can examine fiscal and ecological implications of strategic water conservation strategies.

Bibliogaphy

• Hiessel, H.I., 2002. The German Water Sector, Policies and Experiences, Report for the German Federal Minister for the Environment. http://www.umweltbundesamt.org/wsektor/wasserdoku/english/doku_e.pdf
• Forster, H.S.J., Beattie, B.R., 1979. Urban residential water demand for water in the United States. Land Economics 55(1) pp. 43-58.
• Garcia, A.F., Valinas Garcia, A.M., Espineria-Martinez, R., (2001). The Literature on the Estimation of Residential Water Demand, Elsevier Science
• Martin, W.E., Ingram, H.M., Laney, N.K., Griffin, A.,H., 1994. Saving Water in a Desert City. The John Hopkins University Press, Resources for the Future, Baltimore, USA.

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