Lower Malad Sub Watershed Analysis and Its Effect on the Bear River Migratory Bird Refuge

By Francisco Suero

Overview

The Lower Malad sub watershed is part of the Bear River Basin. It’s located between longitudes 111⁰W and 113⁰ W and between the latitudes 41⁰N and 43⁰N. It’s cut almost in half by the border between the state of Utah and the state of Idaho. The watershed has an area of 3257.55 km². This basin drains into the Great Salt Lake, which is located on the south end. The Great Salt Lake is the lowest elevation in the watershed at 1280 m above sea level.

On the south side of the watershed, the Bear River Migratory Bird Refuge is located, where the Bear River flows into the Great Salt Lake. The wetlands in the Bird Refuge are the biggest freshwater source in the Great Salt Lake and in the deserted area where it’s located.

These wetlands are far from what they used to be due to the large amount of water that is diverted from the river and used for irrigation purposes. Even with a smaller wetland area, migratory birds still come every year in quantities in the order of millions.

In 1983, after years of record precipitation, the Salt Lake rose. The lake level went up so much that it flooded the Bird Refuge, mixing its saline water with the fresh water in the refuge. This flood event stopped the refuge for working for a few years.

In 1990, after the lake water level went down and the Refuge structures where visible again, work was started to recondition the area for the Bird Refuge.

In this paper, I’m going to try to identify what variables (precipitation, evaporation, flow rate) from the basin and flowing into the Bird Refuge influence the most in having the birds come to this particular area in such a large volume each year. The data obtained about the birds that come to the Refuge is from 2006 and 2007, reason why the records of precipitation, evaporation and flow rate were also selected for that period.

Topography

The Lower Malad Sub Watershed has a highest elevation of 2,855m at Box Elder Peak, and a minimum elevation of 1,280m at the Great Salt Lake; with a mean elevation of 1571m and a range of 1,284m.

Existing Structures

There are six dams in the basin:

DAM_NAME	LONGITUDE	LATITUDE
BOX ELDER CREEK (CHATFIELD)	-111.9150	41.4467
MANTUA	-111.9417	41.5017
CROWTHER	-112.2571	42.2033
DEEP CREEK	-112.1728	42.2101
DEVIL CREEK	-112.2062	42.2948
DANIELS	-112.4424	42.3455

Beside the dams, there are diversion structures that take water for the rivers for irrigation purposes.

Hydrography

The major streams of the Lower Malad Sub Watershed are:

· Bear River

· Dairy Creek

· Little Malad River

· Malad River

The Malad River is the major tributary of the watershed, flowing into the Bear River.

The average flow rate of the Bear River entering the Bird Refuge is measured at a USGS gage near Corrine (ID 10126000). Since the study is being made for the amount of birds per season, the flow was also averaged by season.

	Flowrate (cfs)
Spring	2518.60
Summer	288.75
Fall	715.65
Winter	1389.69

The highest flow is in the spring due to the snowmelt, and the lowest flow is in the fall due to the amount of water used during the summer for irrigation purposes.

Climate

For the study, precipitation and evaporation were analyzed. This data was obtained from weather stations in the basin and around it.

The stations used were:

The average precipitation in the basin during the years of the study was:

The lowest average precipitation is in the summer with 1.46 in and the highest in the spring with 4.40 in.

I also looked at the precipitation per season in each year and the results are these:

	2006	2007
	Precipitation (in)	Precipitation (in)
Spring	5.36	3.43
Summer	1.87	1.05
Fall	4.30	2.41
Winter	4.34	3.26

As we can see in the chart above, 2007 had lower precipitation than 2006 in each of the seasons. The largest difference is the fall with two inches.

Next, I present the average evaporation for the study period.

The highest evaporation is the summer with 15 inches. This high evaporation contrasts with the low precipitation for that season (1.46 in).

When we look at the data by year we get:

	2006	2007
	Evaporation (in)	Evaporation (in)
Spring	3.27	8.28
Summer	19.22	11.53
Fall	7.83	4.99
Winter	1.15	1.96

As we can see in the table, there is not a clear pattern of seasonal evaporation. In 2006, the evaporation in the summer was twice the evaporation in the spring, but in 2007 it was the opposite.

Bird Data

The Bear River Migratory Bird Refuge does surveys a few times per month to quantify the amount of birds. The birds are counted by people, therefore the huge uncertainty in the results.

The bird count for 2006 and 2007 is the following:

	2006	2007	Average
	Number of Birds	Number of Birds
Spring	5,937,343	6,395,393	6,166,368
Summer	4,113,848	10,011,211	7,062,530
Fall	11,141,526	9,630,004	10,385,765
Winter	2,362,063	760,705	1,561,384

The biggest difference between the two years is the number of birds in the summer, having2007 more than twice the number of birds in 2006. Also, in the 2007 winter, the number of birds drops considerably from the number of birds for that season the year before.

Analysis

When all the data obtained is combined we have:

2006
	Flowrate (cfs)		Precipitation (in)		Evaporation (in)			Number of Birds
Spring	3774		5.36		3.27			5,937,343
Summer	491		1.87		19.22			4,113,848
Fall	1016		4.30		7.83			11,141,526
Winter	1603		4.34		1.15			2,362,063
2007
	Flowrate (cfs)		Precipitation (in)		Evaporation (in)			Number of Birds
Spring	1264		3.43		8.28			6,395,393
Summer	87		1.05		11.53			10,011,211
Fall	415		2.41		4.99			9,630,004
Winter	1176		3.26		1.96			760,705
Average
		Flowrate (cfs)		Precipitation (in)		Evaporation (in)	Birds
Spring		2518.60		4.40		5.78	6,166,368
Summer		288.75		1.46		15.38	7,062,530
Fall		715.65		3.36		6.41	10,385,765
Winter		1389.69		3.80		1.56	1,561,384

The analysis is done for eight observations, being them each season for 2006 and 2007. The variables are used as input in a semi-log regression to obtain the number of birds as the output. A linear regression was tried first but the fitting was very poor.

These are the results obtained:

Regression Statistics
Multiple R	0.88
R Square	0.78
Adjusted R Square	0.62
Standard Error	2304233.127
Observations	8

Variables	Coefficients	t Stat	P-value
Intercept	37931589.91	3.01	0.03
Flowrate (cfs)	-8201388.811	-3.01	0.03
Precipitation (in)	17504401.23	2.92	0.04
Evaporation (in)	2659864.364	2.26	0.08

The results provide a good fitting with a R² of 0.78. According to the results all the variables used appear to be statistically significant at a 90% level, being the least significant the evaporation in the basin.

The equation to obtain the number of birds in the Bear River Migratory Bird Refuge can be expressed as:

-8201388 Ln Flow rate + 17504401 Ln Precipitation + 2659864 Ln Evaporation + 37931589 = Number of Birds

Conclusions

After having analyzed climatologic and hydrologic data for the Lower Malad Sub Watershed and its impact in the Bear River Migratory Bird Refuge, a direct relationship has been obtained. The results of this study provide a way to estimate the number of birds for a season based on hydrologic and climatologic variables, in this case, precipitation, evaporation and flow rate. The uncertainty of the amount of birds is an important factor on these results, but there is no way to account for that due to having only two surveys per month at the most. This uncertainty could be lowered by having more frequent surveys throughout the year

Further study should be made with more bird data in order to have more observations and therefore a more significant response. Also, it would be appropriate to consider more variables such as temperature and snow, for example. Temperature wasn’t considered in this study due to the amount of missing data in the weather stations for the study period. Biological data isn’t consider in this study, which could also provide a more precise way to determine the factors that influence the birds on coming to this particular place .

References:

Maidment, David. Arc Hydro GIS for Water Resources. ESRI Press, 2002.

Bear River Basin: Planning for the Future.

(http://www.water.utah.gov/planning/SWP/bear/bearindex2004.htm)

Bear River Migratory Bird Refuge.

(http://www.fws.gov/bearriver/index.html)

Utah GIS Portal.

(http://gis.utah.gov)

Bear River Watershed Information System.

(http://bearriverinfo.org)

National Hydrography Dataset.

(http://www.horizon-systems.com/nhdplus)

United States Geological Survey. USGS.

(http://water.usgs.gov)