Abstract Title

Session S-06G: Integrating Landscape Scale Assessments Into Local Planning I

Keywords

Planning Assessment & Communication

Location

Room 6E

Start Date

1-5-2014 1:30 PM

End Date

1-5-2014 3:00 PM

Description

In 2008, the US EPA and King County initiated a five year (2007 to 2012) assessment of land use effects and regulatory effectiveness on the County’s lowland rural streams and watersheds. As part of this effort, a Hydrologic Condition Index (HCI) was developed to quantify the hydrologic effect of land cover change in a way that would be comparable across space and time scales. In order to develop the HCI, the combined effect of geology and land cover on high pulse counts (HPCs, a measure of hydrologic flashiness) was modeled using a 61-year precipitation record for five lowland watersheds of western King County. The models provided average HPCs for each unique combination (24 total) of geology (till and outwash) and twelve land covers, ranging in potential number of HPCs from forest, producing the fewest, to paved road, producing the most. For all statistics run (Pearson, R square etc), modeled results were rated as fair or better in predicting HPCs. Meanwhile, in nine separate study watersheds (six treatment, three reference) used to assess regulatory effectiveness, watershed area was broken into (1.8 m) grid cells and grid cell distances from the watershed monitoring point were calculated and inverted (i.e., 1/distance) to make the relative hydrologic effect of land cover change within small distances from a monitoring point “large” and vice versa. The modeled HPC for a given grid cell’s combination of geology and land cover was weighted (multiplied) by the grid cell’s inverted distance and products were then summed to create a watershed score. To calculate the HCI, the resulting watershed scores were divided by the score for the worst possible (all paved road) condition. To put hydrologic change during project timeframe in perspective with modeled past and potential future conditions and to provide comparison with an urban condition, HCIs were estimated for project timeframe, historic (ca 1910, 1936 and 1965), full build out and reference (combinations of forest, grass and impervious) conditions and a representative urban watershed (Juanita Creek). Results suggest that the HCI is a precise and useful tool for quantifying and evaluating the effect of land use and associated land cover change on stream hydrology and may be suitable for use in other lowland “glacial drift” watersheds in Puget Sound.

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May 1st, 1:30 PM May 1st, 3:00 PM

The derivation and utility of a hydrologic condition index for assessing land use effects and regulations

Room 6E

In 2008, the US EPA and King County initiated a five year (2007 to 2012) assessment of land use effects and regulatory effectiveness on the County’s lowland rural streams and watersheds. As part of this effort, a Hydrologic Condition Index (HCI) was developed to quantify the hydrologic effect of land cover change in a way that would be comparable across space and time scales. In order to develop the HCI, the combined effect of geology and land cover on high pulse counts (HPCs, a measure of hydrologic flashiness) was modeled using a 61-year precipitation record for five lowland watersheds of western King County. The models provided average HPCs for each unique combination (24 total) of geology (till and outwash) and twelve land covers, ranging in potential number of HPCs from forest, producing the fewest, to paved road, producing the most. For all statistics run (Pearson, R square etc), modeled results were rated as fair or better in predicting HPCs. Meanwhile, in nine separate study watersheds (six treatment, three reference) used to assess regulatory effectiveness, watershed area was broken into (1.8 m) grid cells and grid cell distances from the watershed monitoring point were calculated and inverted (i.e., 1/distance) to make the relative hydrologic effect of land cover change within small distances from a monitoring point “large” and vice versa. The modeled HPC for a given grid cell’s combination of geology and land cover was weighted (multiplied) by the grid cell’s inverted distance and products were then summed to create a watershed score. To calculate the HCI, the resulting watershed scores were divided by the score for the worst possible (all paved road) condition. To put hydrologic change during project timeframe in perspective with modeled past and potential future conditions and to provide comparison with an urban condition, HCIs were estimated for project timeframe, historic (ca 1910, 1936 and 1965), full build out and reference (combinations of forest, grass and impervious) conditions and a representative urban watershed (Juanita Creek). Results suggest that the HCI is a precise and useful tool for quantifying and evaluating the effect of land use and associated land cover change on stream hydrology and may be suitable for use in other lowland “glacial drift” watersheds in Puget Sound.