Runoff from the Local Official Perspective (4-D Temporal)

The researcher perspective showed the factors that affect the runoff process. The conservationist perspective showed monitored stream flow for the Spring Creek Watershed. The local official perspective include ideas from both of these perspectives and views water resources from a decision making standpoint.
 

When it comes to water resources, local government officials are concerned with how their local planning decisions and policies will affect water resources. The ability to predict future water resource levels requires the use of a hydrologic model. InterWET used the Generalized Watershed Loading Functions (GWLF) model to predict future conditions in the Spring Creek Watershed. Using a variety of information sources (detailed in the on-line dissertation on InterWET), GWLF was used to model water quantity and quality for eight subwatersheds of the Spring Creek Watershed. Four of these subwatersheds corresponded to four locations along Spring Creek: Oak Hall, Houserville, Axeman, and Milesburg. The other four subwatersheds corresponded to the four main tributaries to Spring Creek: Logan Branch, Buffalo Run, Cedar Run, and Slab Cabin Run. The map below shows the four locations along Spring Creek and the four tributaries. Modeling of the four Spring Creek locations considered all land areas upstream from that location. Therefore, the Milesburg subwatershed included almost the entire watershed, and the others smaller portions of the watershed.

Source Data for map: Environmental Resources Research Institute at The Pennsylvania State University.

The two tables below compare the GWLF Model predictions with the monitored values from the conservationist perspective.

Spring Creek Mean Flows: Monitored and Modeled

Spring Creek Tributaries Mean Flows: Monitored and Modeled

Notice for Spring Creek, the predicted flows for Milesburg and Oak Hall closely agree with the measured flows. However, Houserville and Axeman have lower actual flows than those predicted the model. This is due to groundwater drainage in the watershed. The GWLF model assumes that all groundwater flow in a surface subwatershed stays in that watershed. The groundwater from the conservationist perspective web page showed that a large portion of the groundwater flow discharge into streams and spring near Bellefonte. Notice how in the Spring Creek Tributaries table that Logan Branch flow was under predicted and all other flows were over predicted. However, the total flow contributed by the tributaries is approximately the same.  This problem with GWLF will only affect the predictions of total runoff and groundwater flow.  All runoff, sediment, and nutrient predictions are primarily based on surface conditions (land cover, soils), not the subsurface geology.

The tables below give GWLF's predictions of runoff and stream flow for Spring Creek and its tributaries based on 20 year of simulated weather.

Projected Mean Surface Runoff and Stream Flows for Spring Creek
Over the Next 20 Years Based on Current Local Policies

Projected Mean Surface Runoff and Stream Flows for Spring Creek Tributaries
Over the Next 20 Years Based on Current Local Policies

As mentioned earlier, the runoff predictions should be fairly reliable.  The actual stream flow or total runoff will be less for Spring Creek at Axeman and Houserville and for Buffalo Run, Cedar Run, and Slab Cabin Run.  The actual stream flow will be greater for Logan Branch.

By using of a hydrologic model like GWLF, local officials can forecast how particular local policies may affect water resource levels.  The calculator below shows how a certain set of policies may affect surface runoff.

Click the button below to load the Runoff Calculator.

The calculator can be resized for your screen.

Source Data for map: Environmental Resources Research Institute at The Pennsylvania State University.
 

Explanation of Policies

Riparian Zone protection was based on control of sediment delivery. GWLF does not account for in-stream erosion, but does use a sediment delivery ratio (SDR) based of the area of the subwatershed. The policy choice of ‘less protection’ sets the SDR at a maximum value.  The policy choice of ‘total protection’ sets the SDR to a minimum at value. The choice ‘no change’ kept the SDR at the value based on subwatershed area, and the ‘more protection’ option placed the SDR at half way between the area-based value and minimum value.

The wastewater management policies are based around whether homes use septic systems or sewer. Loads to either septic and sewer are based on projected population increases. The different choices determine if the current
percent of septic and sewer levels are maintained during growth, if all new growth has sewer
or septic, or if all wastewater becomes sewered.

The final set of policy choices are concerned with agricultural BMPs. One BMP was to eliminate land application of manure, which is assumed to occur during winter months.  The other two BMPs implemented contour or chisel tillage, which reduces the amount of detached sediment.

The output from the calculator reflects the mean annual change in the runoff cause by a particular set of policies.  After selecting a set of policies, before clicking calculate, be sure to select whether to display the change as a percentage or in one of the 8 categories listed in the table below.

Percent Change Categories
 

Category	Percent Change Range
Large Decrease	X<-50
Medium Decrease	-50<=X<-25
Slight Decrease	-25<=X<-10
No Change	-10<=X<+10
Slight Increase	+10<=X<+25
Medium Increase	+25<=X<+50
Large Increase	+50<=X<+100
Very Large Increase	+100<=X

Experiment with policies and see how each kind of policy affects the surface runoff.  The relationships that were shown in the researcher perspective still hold for these calculator.  The only policies that affect surface runoff are those policies which affect land cover or soil.  Consequently, the only policies which affect surface runoff are Land Use policies.  Notice that this effect is small.  Most of the changes percentages fall within the No Change category.

GWLF was also used to model changes in total runoff caused by policy change.  No change were found to occur to the mean annual total runoff.  On an annual basis, total runoff will not change, because the evapotranspiration in each subwatershed is not significantly impacted by the land use change caused by the policies.
 

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