Potential Future Studies

This study provides a basis for potential future investigation to enhance our knowledge of the Johnson Creek basin hydrologic system and of the possible effects of land-use changes in the basin. For example, further studies to examine the groundwater flow system could provide information about contributing areas and an insight into the relation between springs and streams within the Johnson Creek basin and throughout the Portland metropolitan area. The installation of a broader network of monitoring wells and development of a fine grid flow model are two efforts that would be of use in gaining a better understanding of the area. Installation of more wells distributed throughout the basin and adjacent areas, with data collection on a decade time-scale would provide the data necessary for increased understanding of groundwater flow and of groundwater interaction with Johnson Creek and tributary streams. And the fine-grid flow model could provide a finer discretization than was previously possible with the coarse-grid regional model made in the 1990s (Morgan and McFarland, 1996).

Identification of groundwater contributing areas of features such as Crystal Springs Creek and Holgate Lake would allow for better determination of causes for variations in streamflow and water levels and provide for greater opportunities for resource protection. Specific to Crystal Springs Creek, further investigation into trends in water levels in wells could lead to better understanding of fluctuations in streamflow. Better understanding of the connection of the aquifer in the Westmoreland Park area to Crystal Springs Creek, Johnson Creek, and the Willamette River, could provide insight into water-level fluctuations in this area. A more detailed analysis of water levels, streamflow, and an elevation survey of the key components in the Westmoreland Park area, including springs, wells, and the creek, also would contribute to an understanding of water level fluctuations.

The groundwater flow system in the volcanic buttes on the southern side of the Johnson Creek basin is not well understood. Dense urban development of this area could lead to negative effects on the hydrology of this area of the basin. Refinements in knowledge of the groundwater flow system and understanding of water uses in the basin could provide guidance to managers on the effects of present and future water withdrawals, and on the effects of land-use changes on base flows of the creeks in this area of the basin.

In the surface-water realm, future study could provide understanding of runoff characteristics of upland areas, particularly on the southern side of the basin, and especially relative to future urban expansion. Analysis of the impact of “green” development, where stormwater is infiltrated onsite, could be compared in a paired-basin study to assess the effectiveness of these measures on flood frequency. From a historical perspective, analyses could be made of the impact of past land-use practices, such as stormwater-disposal methods, on stream response.

Numerous nearstream restoration projects have been completed in the Johnson Creek basin, and more are planned in the coming decades. Several projects involve returning the constructed trapezoidal stream channel to a more natural configuration. The effect of these projects on moderation of high flows and augmentation of groundwater recharge through use of overbank and backwater areas has not been determined. Continued flow monitoring could yield understanding of possible changes in peak streamflow and peak volume. Additional time-of-travel (dye-tracer) studies could provide insight into the effectiveness of the restored features in terms of the timing and dispersive characteristics of the stream.

High stream temperature and sediment (and sediment-transported contaminants) are problems for water quality in the Johnson Creek basin. Future studies could provide understanding of the effect of measures to reduce thermal loading, such as revegetation, removal of instream ponds, and securing instream water rights. Channel-modification measures underway in 2008 may have an effect on the transport and deposition of sediment in the basin. Understanding of the effect of these changes on sediment transport processes may help guide future restoration work in the Johnson Creek basin.