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

The Generalized Watershed Loading Functions (GWLF) Model was used to predict detached and delivered sediment flow 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 its four tributaries.

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

The tables below give GWLF's estimates of detached sediment in the subwatersheds of Spring Creek and its tributaries for the past 20 years based on observed weather data and predictions for the next 20 years based on simulated weather data.  Remember that detached sediment refers to "gross" erosion, while delivered sediment refers to the sediment that is delivered to a stream.

Predicted Mean Detached Sediment for Spring Creek Subwatershed
for the Past 20 Years and for the Next 20 Years

Predicted Mean Detached Sediment for Spring Creek Tributaries
for the Past 20 Years and for the Next 20 Years

Notice which subwatersheds are the sources of the most sediment: Cedar Run and Logan Branch. Remember the factors from the sediment from the researcher perspective web page that affect detached sediment:  land cover, soils, slope and slope length.  These higher sediment producing subwatersheds tend to have more agriculture and higher sloped soils along Mount Nittany.

The tables below compare  GWLF's estimates of delivered sediment in the subwatersheds of Spring Creek and its tributaries for the past 20 years with measured value from the sediment from the conservationist web page.

Comparison of Measured and Predicted Delivered Sediment for Spring Creek

Location	Measured (mg/l)	Predicted (mg/l)
Milesburg	28.0	28.2
Near Axeman	57.7	30.8
Houserville	11.2	45.5
Oak Hall	7.9	34.0

Comparison of Measured and Predicted Delivered Sediment for Spring Creek Tributaries

Location	Measured (mg/l)	Predicted (mg/l)
Logan Branch	5.1	81.3
Buffalo Run	6.4	42.9
Cedar Run	31.9	130.4
Slab Cabin Run	95.2	36.2

 

This comparison shows the difficulty of using a simple hydrologic model to predict sediment delivery.  GWLF uses a single sediment delivery ratio (SDR) factor for each subwatershed.  This factor is based on the watershed area.  Notice how the predicted delivered sediment decreases as the area of the subwatershed increases.  Unfortunately, the measured data is also far from perfect.  Remember from the sediment from the conservationist perspective web page that these prediction are flow adjusted means and for certain locations are based on only a few values.  The actual delivered sediment in the stream of the Spring Creek Watershed are probably somewhere between the measured and the predicted values.  The actual sediment level for the locations along Spring Creek are probably higher than the predicted levels, and probably lower than the tributary predictions.  Again, this points to the need of addition monitoring.

The tables below shows the predicted sediment delivery for the next 20 years, based on simulated weather data.
 

Predicted Mean Delivered Sediment for Spring Creek Subwatershed
for the Next 20 Years

Predicted Mean Delivered Sediment for Spring Creek Tributaries
for the Next 20 Years

Below are buttons to bring up a calculator for detached sediment change and delivered sediment change based on local policy changes.

Click the button below to load the Sediment Detachment Calculator.

Click the button below to load the Sediment Delivery Calculator.

Each calculator can be resized for your screen.

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

The output from each calculator reflects the mean annual change in the groundwater flow caused by a particular set of policies.  For the detached sediment calculator, 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.  The delivered sediment only displays change in the 8 categories, due to the complexity of the modeling.

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

First, using the detached sediment calculator, experiment with policies and see how each kind of policy affects the detached sediment.  Notice that relationships that were shown in the researcher perspective still hold for this calculator.  Detached sediment is affect by soils, slope and slope length, and land cover and management.  Consequently, the only policies which affect detached sediment are Land Use policies and Agricultural Best Management Practices (BMPs).  Notice that the proper combination of policies can greatly the detached sediment.

Now experiment with the delivered sediment calculator.  Not only do Land Cover and Ag. BMP policies affect delivered sediment, but so do Riparian policies.  Remember that riparians do not impact sediment detachment, but do impact sediment delivery.  This shows that riparian protection can help keep streams cleaner, but does not eliminate the source of the sediment.

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