manually through a variety of methods including examining com- mercial Facebook and Yelp accounts, driving Google Street View, and other online records. The address similarity tool was validated with the use of a third-party geospatial analysis tool. The results of the validation indicated an er- ror rate of approximately 0.06 percent. In total, three address matches above the 0.75 threshold were made in error and were corrected manually. Fee Calculation The Equivalent Residential Unit (ERU) is a value that represents the amount of impervious surface found on the hypothetical typical single- family residential home in a community. The U.S. EPA estimates that 80 percent of stormwater utility fees are based on the ERU concept. Zoning information allowed for the identification of single-family residential parcels at Mineral Wells. When examined, the average typical single-family parcel (excluding undeveloped areas zoned as single-family residential) exhibited approximately 2,600 square feet of impervious surface. Thus, the ERU for the City of Mineral Wells was determined to be 2,600 square feet of impervious surface. NewGen Solutions took the impervious surface data developed by LAN and financial data from the city and determined that a per-ERU fee of $3.89 would fully fund the stormwater utility over the next five years. If every utility billing customer pays $3.89 per ERU on their property, the city will be able to recover the necessary funds to repair, maintain, expand, and ensure that high-quality stormwater services are provided to the residents. A $3.89 per ERU fee is within the range of $2.50 - $6.50 fees seen in similar communities in Texas. Under this proposed billing scheme, all single-family residential utility billing customers would pay $3.89 to the stormwater utility, regardless of actual impervious surface coverage. This simplification reduces ad- ministrative burdens on the City and is common practice in stormwater utilities. All non-single-family utility billing customers would pay on a true ERU-based schedule at a rate of $3.89 per ERU. The City currently bills a $2.50 flat rate stormwater fee for all utility billing customers, regardless of impervious surface or property type. A jump from a flat rate of $2.50 to an ERU-based billing schedule at $3.89 per ERU will increase the amount that most utility customers would pay. A few commercial properties with relatively little impervi- ous surface would see a reduction below the $2.50 per month rate. To ease the transition to an ERU-based system, it is possible that the City may begin with a $2.50 per ERU rate. As all single-family residential customers are billed at 1 ERU, single family residential customers would see no change to their billing rates. This introductory rate may eventually increase over time to the $3.89 per ERU rate. By using a publicly announced rate schedule that slowly trends towards the fully funded $3.89 per ERU rate, the City of Mineral Wells can allow utility billing customers to plan and budget in advance of any rate changes. Ultimately, the decisions of City Council will determine the rate set- ting method.
The composite dataset created by combining the three machine learning datasets. Each color represents a unique combination of results from the three input datasets. Photo: LAN
By standardizing addresses and breaking them out into their com- ponents, a constituent level comparison could be made. In this com- parison, every utility billing account address was compared to every parcel address and returned a similarity score from 0 (no similarity) to 1 (perfect match). In this comparison, no tolerance for deviation was allowed in the street number or street direction. While similar to 123 N Example St, 125 N Example St is a different address and does not represent a matching error. Similarly, 123 N Example St and 123 S Example St also do not represent a matching error and may be quite geographically distant from each other. Tolerance for errors on street name and street suffix was allowed. For example, the pair of 123 N Example St and 123 N Example would return high similarity scores. 123 N Example St and 123 N Exmple St would also return high similarity scores. The address similarity tool ran comparisons between every utility bill- ing account address and every parcel address. This raw comparison produced roughly 70 million address match combinations. It was as- sumed that the highest scoring match for each utility billing address represented the correct parcel match. An arbitrary similarity score threshold of 0.75 was set to separate correctly matched (≥0.75) and incorrectly matched (<0.75) pairs. The 0.75 threshold represents a conservative cutoff point for matching acceptance. A match of 123 N Example St and 123 N Exmple St would return a score of 0.916 and a match of 123 N Example St and 123 N Example would return a score of 0.75. Incorrectly matched utility billing accounts were matched The composite dataset created by combining the three machine learning datasets. Each color represents a unique combination of results from the three input datasets. Photo: LAN
TAK M. MAKINO, CFM, is a Flood Mitigation Manager at Lockwood, Andrews & Newnam, Inc. (LAN), a national planning, engineering and program manage- ment firm. He can be reached at tmmakino@lan-inc.com.
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csengineermag.com march 2020
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